.NET
FrameWork
When was .NET announced?
Bill Gates delivered a keynote at Forum 2000, held
June 22, 2000, outlining the .NET 'vision'. The July 2000 PDC had a number of
sessions on .NET technology, and delegates were given CDs containing a
pre-release version of the .NET framework/SDK and Visual Studio.NET.
When was the first version of .NET released?
The final version of the 1.0 SDK and runtime was
made publicly available around 6pm PST on 15-Jan-2002. At the same time, the
final version of Visual Studio.NET was made available to MSDN subscribers.
What platforms does the .NET Framework run on?
The runtime supports Windows XP, Windows 2000, NT4 SP6a and Windows ME/98.
Windows 95 is not supported. Some parts of the framework do not work on all
platforms - for example, ASP.NET is only supported on Windows XP and Windows
2000. Windows 98/ME cannot be used for development.
IIS is not supported on Windows XP Home Edition, and so cannot be used to host
ASP.NET. However, the ASP.NET Web Matrix
web server does run on XP Home.
The Mono project is attempting to implement the .NET framework on Linux.
What is the CLR?
CLR = Common Language Runtime. The CLR is a set of
standard resources that (in theory) any .NET program can take advantage of,
regardless of programming language. Robert Schmidt (Microsoft) lists the
following CLR resources in his MSDN PDC# article:
Object-oriented programming model (inheritance, polymorphism, exception
handling, garbage collection)
Security model
Type system
All .NET base classes
Many .NET framework classes
Development, debugging, and profiling tools
Execution and code management
IL-to-native translators and optimizers
What this means is that in the .NET world, different programming languages will
be more equal in capability than they have ever been before, although clearly
not all languages will support all CLR services.
What is the CTS?
CTS = Common Type System. This is the range of types
that the .NET runtime understands, and therefore that .NET applications can
use. However note that not all .NET languages will support all the types in the
CTS. The CTS is a superset of the CLS.
What is the CLS?
CLS = Common Language Specification. This is a
subset of the CTS which all .NET languages are expected to support. The idea is
that any program which uses CLS-compliant types can interoperate with any .NET
program written in any language.
In theory this allows very tight interop between different .NET languages - for
example allowing a C# class to inherit from a VB class.
What is IL?
IL = Intermediate Language. Also known as MSIL
(Microsoft Intermediate Language) or CIL (Common Intermediate Language). All
.NET source code (of any language) is compiled to IL. The IL is then converted
to machine code at the point where the software is installed, or at run-time by
a Just-In-Time (JIT) compiler.
What does 'managed' mean in the .NET context?
The term 'managed' is the cause of much confusion.
It is used in various places within .NET, meaning slightly different
things.Managed code: The .NET framework provides several core run-time services
to the programs that run within it - for example
exception handling and security. For these
services to work, the code must provide a minimum level of information to the
runtime.
Such code is called managed code. All C# and
Visual Basic.NET code is managed by default. VS7 C++ code is not managed by
default, but the compiler can produce managed code by specifying a command-line
switch (/com+).
Managed data: This is data that is allocated and de-allocated by the
.NET runtime's garbage collector. C# and VB.NET data is always managed. VS7 C++
data is unmanaged by default, even when using the /com+ switch, but it can be
marked as managed using the __gc keyword.Managed classes: This is usually
referred to in the context of Managed Extensions (ME) for C++. When using ME
C++, a class can be marked with the __gc keyword. As the name suggests, this
means that the memory for instances of the class is managed by the garbage
collector, but it also means more than that. The class becomes a fully paid-up
member of the .NET community with the benefits and restrictions that brings. An
example of a benefit is proper interop with classes written in other languages
- for example, a managed C++ class can inherit from a VB class. An example of a
restriction is that a managed class can only inherit from one base class.
What is reflection?
All .NET compilers produce metadata about the types
defined in the modules they produce. This metadata is packaged along with the
module (modules in turn are packaged together in assemblies), and can be
accessed by a mechanism called reflection. The System.Reflection namespace
contains classes that can be used to interrogate the types for a
module/assembly.
Using reflection to access .NET metadata is very similar to using
ITypeLib/ITypeInfo to access type library data in COM, and it is used for
similar purposes - e.g. determining data type sizes for marshaling data across
context/process/machine boundaries.
Reflection can also be used to dynamically invoke methods (see
System.Type.InvokeMember ) , or even create types dynamically at run-time
(see System.Reflection.Emit.TypeBuilder).
What is the difference between Finalize and
Dispose (Garbage collection) ?
Class instances often encapsulate control over
resources that are not managed by the runtime, such as window handles (HWND),
database connections, and so on. Therefore, you should provide both an explicit
and an implicit way to free those resources. Provide implicit control by implementing
the protected Finalize Method on an object (destructor syntax in C# and the
Managed Extensions for C++). The garbage collector calls this method at some
point after there are no longer any valid references to the object. In some
cases, you might want to provide programmers using an object with the ability
to explicitly release these external resources before the garbage collector
frees the object. If an external resource is scarce or expensive, better
performance can be achieved if the programmer explicitly releases resources
when they are no longer being used. To provide explicit control, implement the
Dispose method provided by the IDisposable Interface. The consumer of the
object should call this method when it is done using the object.
Dispose can be called even if other references
to the object are alive. Note that even when you provide explicit control by
way of Dispose, you should provide implicit cleanup using the Finalize method.
Finalize provides a backup to prevent resources from
permanently leaking if the programmer fails to
call Dispose.
What is Partial Assembly References?
Full Assembly reference: A full assembly
reference includes the assembly's text name, version, culture, and public key
token (if the assembly has a strong name). A full assembly reference is
required if you reference any assembly that is part of the common
language runtime or any assembly located in
the global assembly cache.
Partial Assembly reference: We can dynamically
reference an assembly by providing only partial information, such as specifying
only the assembly name. When you specify a partial assembly reference, the
runtime looks for the assembly only in the application
directory.
We can make partial references to an assembly in your code one of the following
ways:
-> Use a method such as System.Reflection.Assembly.Load and specify only a
partial reference. The runtime checks for the assembly in the application
directory.
-> Use the System.Reflection.Assembly.LoadWithPartialName method and specify
only a partial reference. The runtime checks for the assembly in the
application directory and in the global assembly cache
Changes to which portion of version number
indicates an incompatible change?
Major or minor. Changes to the major or minor
portion of the version number indicate an incompatible change. Under this
convention then, version 2.0.0.0 would be considered incompatible with version
1.0.0.0. Examples of an incompatible change would be a change to the types of
some method parameters or the removal of a type or method altogether. Build.
The Build number is typically used to distinguish between daily builds or
smaller compatible releases. Revision. Changes to the revision number are
typically reserved for an incremental build needed to fix a particular bug.
You'll sometimes hear this referred to as the "emergency bug fix"
number in that the revision is what is often changed when a fix to a specific
bug is shipped to a customer.
What is side-by-side execution? Can two
application one using private assembly and other using Shared assembly be
stated as a side-by-side executables?
Side-by-side execution is the ability to run
multiple versions of an application or component on the same computer. You can
have multiple versions of the common language runtime, and multiple versions of
applications and components that use a version of the runtime, on the same
computer at the same time. Since versioning is only applied to shared
assemblies, and not to private assemblies, two application one using private
assembly and one using shared assembly cannot be stated as side-by-side
executables.
Why string are called Immutable data Type
?
The memory representation of string is an Array of
Characters, So on re-assigning the new array of Char is formed & the start
address is changed . Thus keeping the Old string in Memory for Garbage
Collector to be disposed.
What does assert() method do?
In debug compilation, assert takes in a Boolean condition as a parameter, and
shows the error dialog if the condition is false. The program proceeds
without any interruption if the condition is true.
What's the difference between the Debug class
and Trace class?
Documentation looks the same. Use Debug class
for debug builds, use Trace class for both debug and release builds.
Why are there five tracing levels in
System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose. For applications that are
constantly running you run the risk of overloading the machine and the hard
drive. Five levels range from None to Verbose, allowing you to fine-tune
the tracing activities.
Where is the output of TextWriterTraceListener
redirected?
To the Console or a text file depending on the
parameter passed to the constructor.
How do assemblies find each other?
By searching directory paths. There are several factors which can affect the
path (such as the AppDomain host, and application configuration files), but for
private assemblies the search path is normally the application's directory and
its sub-directories. For shared assemblies, the search path is normally same as
the private assembly path plus the shared assembly cache.
How does assembly versioning work?
Each assembly has a version number called the
compatibility version. Also each reference to an assembly (from another
assembly) includes both the name and version of the referenced assembly.The
version number has four numeric parts (e.g. 5.5.2.33). Assemblies with either
of the first two parts different are normally viewed as incompatible. If the
first two parts are the same, but the third is different, the assemblies are
deemed as 'maybe compatible'. If only the fourth part is different, the
assemblies are deemed compatible. However, this is just the default guideline -
it is the version policy that decides to what extent these rules are enforced.
The version policy can be specified via the application configuration file.
What is garbage collection?
Garbage collection is a system whereby a run-time component takes
responsibility for managing the lifetime of objects and the heap memory that
they occupy. This concept is not new to .NET - Java and many other
languages/runtimes have used garbage collection for some time.
Why doesn't the .NET runtime offer
deterministic destruction?
Because of the garbage collection algorithm. The
.NET garbage collector works by periodically running through a list of all the
objects that are currently being referenced by an application. All the objects
that it doesn't find during this search are ready to be destroyed and the
memory reclaimed. The implication of this algorithm is that the runtime doesn't
get notified immediately when the final reference on an object goes away - it
only finds out during the next sweep of the heap.
Futhermore, this type of algorithm works best by performing the garbage collection
sweep as rarely as possible. Normally heap exhaustion is the trigger for a
collection sweep.
Is the lack of deterministic destruction in
.NET a problem?
It's certainly an issue that affects component
design. If you have objects that maintain expensive or scarce resources (e.g.
database locks), you need to provide some way for the client to tell the object
to release the resource when it is done. Microsoft recommend that you provide a
method called Dispose() for this purpose. However, this causes problems for
distributed objects - in a distributed system who calls the Dispose() method?
Some form of reference-counting or ownership-management mechanism is needed to
handle distributed objects - unfortunately the runtime offers no help with
this.
What is serialization?
Serialization is the process of converting an object
into a stream of bytes. Deserialization is the opposite process of creating an
object from a stream of bytes. Serialization / Deserialization is mostly used
to transport objects (e.g. during remoting), or to persist
objects (e.g. to a file or database).
Does the .NET Framework have in-built support
for serialization?
There are two separate mechanisms provided by the
.NET class library - XmlSerializer and SoapFormatter/BinaryFormatter. Microsoft
uses XmlSerializer for Web Services, and uses SoapFormatter/BinaryFormatter for
remoting. Both are available for use in your own code.
Can I customize the serialization process?
Yes. XmlSerializer supports a range of attributes
that can be used to configure serialization for a particular class. For
example, a field or property can be marked with the [XmlIgnore] attribute to
exclude it from serialization. Another example is the [XmlElement]
attribute, which can be used to specify the
XML element name to be used for a particular property or field.
Serialization via SoapFormatter/BinaryFormatter can also be controlled to some
extent by attributes. For example, the [NonSerialized] attribute is the
equivalent of XmlSerializer's [XmlIgnore] attribute. Ultimate control of the
serialization process can be acheived by implementing the ISerializable
interface on the class whose instances are to be serialized.
Why is XmlSerializer so slow?
There is a once-per-process-per-type overhead with
XmlSerializer. So the first time you serialize or deserialize an object of a
given type in an application, there is a significant delay. This normally
doesn't matter, but it may mean, for example, that XmlSerializer is a poor
choice for loading configuration settings during startup of a GUI application.
Why do I get errors when I try to serialize a
Hashtable?
XmlSerializer will refuse to serialize instances of
any class that implements IDictionary, e.g. Hashtable. SoapFormatter and
BinaryFormatter do not have this restriction.
What are attributes?
There are at least two types of .NET attribute. The
first type I will refer to as a metadata attribute - it allows some data to be
attached to a class or method. This data becomes part of the metadata for the
class, and (like other class metadata) can be accessed via reflection.
The other type of attribute is a context attribute. Context attributes use a
similar syntax to metadata attributes but they are fundamentally different.
Context attributes provide an interception mechanism whereby instance
activation and method calls can be
pre- and/or post-processed.
How does CAS work?
The CAS security policy revolves around two key
concepts - code groups and permissions. Each .NET assembly is a member of a
particular code group, and each code group is granted the permissions specified
in a named permission set.
For example, using the default security policy, a control downloaded from a web
site belongs to the 'Zone - Internet' code group, which adheres to the
permissions defined by the 'Internet' named permission set. (Naturally the
'Internet' named permission set represents a very restrictive range of
permissions.)
Who defines the CAS code groups?
Microsoft defines some default ones, but you can
modify these and even create your own. To see the code groups defined on your
system, run 'caspol -lg' from the command-line. On my system it looks like
this:
Level = Machine
Code Groups:
1. All code: Nothing
1.1. Zone - MyComputer: FullTrust
1.1.1. Honor SkipVerification requests:
SkipVerification
1.2. Zone - Intranet: LocalIntranet
1.3. Zone - Internet: Internet
1.4. Zone - Untrusted: Nothing
1.5. Zone - Trusted: Internet
1.6. StrongName -
0024000004800000940000000602000000240000525341310004000003
000000CFCB3291AA715FE99D40D49040336F9056D7886FED46775BC7BB5430BA4444FEF8348EBD06
F962F39776AE4DC3B7B04A7FE6F49F25F740423EBF2C0B89698D8D08AC48D69CED0FC8F83B465E08
07AC11EC1DCC7D054E807A43336DDE408A5393A48556123272CEEEE72F1660B71927D38561AABF5C
AC1DF1734633C602F8F2D5:
Note the hierarchy of code groups - the top of
the hierarchy is the most general ('All code'), which is then sub-divided into
several
groups, each of which in turn can be
sub-divided. Also note that (somewhat counter-intuitively) a sub-group can be
associated with a more permissive permission set than its parent.
How do I define my own code group?
Use caspol. For example, suppose you trust code from
www.mydomain.com and you
want it have full access to your system, but you want to keep the default
restrictions for all other internet sites. To achieve this, you would add a new
code group as a sub-group of the
'Zone - Internet' group, like this:
caspol -ag 1.3 -site www.mydomain.com
FullTrust
Now if you run caspol -lg you will see that the new group has been added as
group 1.3.1:
1.3. Zone - Internet: Internet
1.3.1. Site - www.mydomain.com:
FullTrust
Note that the numeric label (1.3.1) is just a
caspol invention to make the code groups easy to manipulate from the
command-line. The underlying runtime never sees it.
How do I change the permission set for a code
group?
Use caspol. If you are the machine administrator,
you can operate at the 'machine' level - which means not only that the changes
you make become the default for the machine, but also that users cannot change
the permissions to be more permissive. If you are a normal (non-admin) user you
can still modify the permissions, but only to make them more restrictive. For
example, to allow intranet code to do what it likes you might do this:
caspol -cg 1.2 FullTrust
Note that because this is more permissive than the default policy (on a
standard system), you should only do this at the machine level - doing it at
the user level will have no effect.
I can't be bothered with all this CAS stuff.
Can I turn it off?
Yes, as long as you are an administrator. Just run:
caspol -s off
Can I look at the IL for an assembly?
Yes. MS supply a tool called Ildasm which can be used to view the metadata and
IL for an assembly.
Can source code be reverse-engineered from IL?
Yes, it is often relatively straightforward to
regenerate high-level source (e.g. C#) from IL.
How can I stop my code being
reverse-engineered from IL?
There is currently no simple way to stop code being reverse-engineered from IL.
In future it is likely that IL obfuscation tools will become available, either
from MS or from third parties. These tools work by 'optimising' the IL in such
a way that reverse-engineering becomes much more difficult.
Of course if you are writing web services then reverse-engineering is not a
problem as clients do not have access to your IL.
Is there built-in support for tracing/logging?
Yes, in the System. Diagnostics namespace. There are two main classes that deal
with tracing - Debug and Trace. They both work in a similar way - the
difference is that tracing from the Debug class only works in builds that have
the DEBUG symbol defined, whereas tracing from the Trace class only works in
builds that have the TRACE symbol defined. Typically this means that you should
use System.Diagnostics.Trace.WriteLine for tracing that you want to work in debug
and release builds, and System.Diagnostics.Debug.WriteLine for tracing that you
want to work only in debug builds.
Can I redirect tracing to a file?
Yes. The Debug and Trace classes both have a
Listeners property, which is a collection of sinks that receive the tracing
that you send via Debug.WriteLine and Trace.WriteLine respectively. By default
the Listeners collection contains a single sink, which is an
instance of the DefaultTraceListener class.
This sends output to the Win32 OutputDebugString() function and also the
System.Diagnostics.Debugger.Log() method. This is useful when debugging, but if
you're trying to trace a problem at a customer site, redirecting the output to
a file is more appropriate. Fortunately, the TextWriterTraceListener class is
provided for this purpose.
What are the contents of assembly?
In general, a static assembly can consist of four
elements:
The assembly manifest, which contains assembly metadata.
Type metadata.
Microsoft intermediate language (MSIL) code that implements the
types.
A set of resources.
What is GC (Garbage Collection) and how it
works
One of the good features of the CLR is Garbage
Collection, which runs in the background collecting unused object references,
freeing us from having to ensure we always destroy them. In reality the time
difference between you releasing the object instance and it being garbage
collected is likely to be very small, since the GC is always running.
[The process of transitively tracing through
all pointers to actively used objects in order to locate all objects that can
be referenced, and then arranging to reuse any heap memory that was not found
during this trace. The common language runtime garbage collector also compacts
the memory that is in use to reduce the working space needed for the heap.]
Heap:
A portion of memory reserved for a program to
use for the temporary storage of data structures whose existence or size cannot
be determined until the program is running.
Difference between Managed code and unmanaged
code ?
Managed Code:
Code that runs under a "contract of
cooperation" with the common language runtime. Managed code must supply
the metadata necessary for the runtime to provide services such as memory
management, cross-language integration, code access security, and
automatic lifetime control of objects. All
code based on Microsoft intermediate language (MSIL) executes as managed code.
Un-Managed Code:
Code that is created without regard for the
conventions and requirements of the common language runtime. Unmanaged code
executes in the common language runtime environment with minimal services (for
example, no garbage collection, limited debugging, and so on).
What is MSIL, IL, CTS and, CLR ?
MSIL: (Microsoft intermediate language)
When compiling to managed code, the compiler translates your source code into
Microsoft intermediate language (MSIL), which is a CPU-independent set of
instructions that can be efficiently converted to native code. MSIL includes
instructions for loading, storing, initializing, and calling methods on
objects, as well as instructions for arithmetic and logical operations, control
flow, direct memory access, exception handling, and other operations. Before
code can be executed, MSIL must be converted to CPU-specific code, usually by a
just-in-time (JIT) compiler. Because the common language runtime supplies one
or more JIT compilers for each computer architecture it supports, the same set
of MSIL can be JIT-compiled and executed on any supported architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes
the types in your code, including the definition of
each type, the signatures of each type's
members, the members that your code references, and other data that the runtime
uses at
execution time. The MSIL and metadata are
contained in a portable executable (PE) file that is based on and extends the
published
Microsoft PE and Common Object File Format
(COFF) used historically for executable content. This file format, which
accommodates
MSIL or native code as well as metadata,
enables the operating system to recognize common language runtime images. The
presence of metadata in the file along with
the MSIL enables your code to describe itself, which means that there is no
need for type libraries or Interface Definition Language (IDL). The runtime
locates and extracts the metadata from the file as needed during
execution.
IL: (Intermediate Language)
A language used as the output of a number of compilers and as the input to a
just-in-time (JIT) compiler. The common language
runtime includes a JIT compiler for converting
MSIL to native code.
CTS: (Common Type System)
The specification that determines how the common language runtime defines,
uses, and manages types
CLR: (Common Language Runtime)
The engine at the core of managed code execution. The runtime supplies managed
code with services such as cross-language
integration, code access security, object
lifetime management, and debugging and profiling support.
What is Reference type and value type ?
Reference Type:
Reference types are allocated on the managed CLR heap, just like object types.
A data type that is stored as a reference to the value's location. The value of
a reference type is the location of the sequence of bits
that represent the type's data. Reference
types can be self-describing types, pointer types, or interface types
Value Type:
Value types are allocated on the stack just like primitive types in VBScript,
VB6 and C/C++. Value types are not instantiated using new go out of scope when
the function they are defined within returns.
Value types in the CLR are defined as types that derive from system.valueType.
A data type that fully describes a value by
specifying the sequence of bits that constitutes the value's representation.
Type information for a value type instance is not stored with the instance at
run time, but it is available in metadata. Value type instances can be treated
as objects using boxing.
What is Boxing and unboxing ?
Boxing:
The conversion of a value type instance to an object, which implies that the
instance will carry full type information at run time and will be allocated in
the heap. The Microsoft intermediate language (MSIL) instruction set's box
instruction converts a value type to an object by making a copy of the value
type and embedding it in a newly allocated object.
Un-Boxing:
The conversion of an object instance to a value type.
What is JIT and how is works ?
An acronym for "just-in-time," a phrase
that describes an action that is taken only when it becomes necessary, such as
just-in-time compilation or just-in-time object activation
What is portable executable (PE) ?
The file format used for executable programs and for
files to be linked together to form executable programs
What is strong name?
A name that consists of an assembly's identity—its simple text name, version
number, and culture information (if provided)—strengthened by a public key and
a digital signature generated over the assembly. Because the assembly manifest
contains file hashes for all the files that
constitute the assembly implementation, it is sufficient to generate the
digital signature over just the one file in the assembly that contains the
assembly manifest. Assemblies with the same strong name are expected to be identical
What is global assembly cache?
A machine-wide code cache that stores assemblies specifically installed to be
shared by many applications on the computer. Applications deployed in the
global assembly cache must have a strong name.
What is difference between constants, readonly
and, static ?
Constants: The value can’t be changed
Read-only: The value will be initialized only once from the constructor of the
class.
Static: Value can be initialized once.
What is difference between shared and public?
An assembly that can be referenced by more than one application. An assembly
must be explicitly built to be shared by giving it a cryptographically strong
name.
What is namespace used for loading assemblies
at run time and name the methods?
System.Reflection
What are the types of authentication in .net?
We have three types of authentication:
1. Form authentication
2. Windows authentication
3. Passport
This has to be declared in web.config file.
What is the difference between a Struct and a
Class ?
The struct type is suitable for representing
lightweight objects such as Point, Rectangle, and Color. Although it is
possible to represent a point as a class, a struct is more efficient in some
scenarios. For example, if you declare an array of 1000 Point objects,
you will allocate additional memory for referencing each object. In this case,
the struct is less expensive.
When you create a struct object using the new operator, it gets created and the
appropriate constructor is called. Unlike classes, structs can be instantiated
without using the new operator. If you do not use new, the fields will remain
unassigned and the object cannot be used until all of the fields are
initialized. It is an error to declare a default (parameterless) constructor
for a struct. A default constructor is always provided to initialize the struct
members to their default values.
It is an error to initialize an instance field in a struct.
There is no inheritance for structs as there is for classes. A struct cannot
inherit from another struct or class, and it cannot be the base of a class.
Structs, however, inherit from the base class Object. A struct can implement
interfaces, and it does that exactly as classes do.
A struct is a value type, while a class is a reference type.
How big is the datatype int in .NET?
32 bits.
How big is the char?
16 bits (Unicode).
How do you initiate a string without escaping
each backslash?
Put an @ sign in front of the double-quoted string.
What's the access level of the visibility type
internal?
Current application.
Explain encapsulation ?
The implementation is hidden, the interface is
exposed.
What data type should you use if you want an
8-bit value that's signed?
sbyte.
Speaking of Boolean data types, what's
different between C# and C/C++?
There's no conversion between 0 and false, as well
as any other number and true, like in C/C++.
Where are the value-type variables allocated
in the computer RAM?
Stack.
Where do the reference-type variables go in
the RAM?
The references go on the stack, while the objects
themselves go on the heap.
What is the difference between the value-type
variables and reference-type variables in terms of garbage collection?
The value-type variables are not garbage-collected,
they just fall off the stack when they fall out of scope, the reference-type
objects
are picked up by GC when their references go
null.
How do you convert a string into an integer in
.NET?
Int32.Parse(string)
How do you box a primitive data type variable?
Assign it to the object, pass an object.
Why do you need to box a primitive variable?
To pass it by reference.
What's the difference between Java and .NET
garbage collectors?
Sun left the implementation of a specific garbage
collector up to the JRE developer, so their performance varies
widely, depending on whose JRE you're using. Microsoft standardized on
their garbage collection.
How do you enforce garbage collection in .NET?
System.GC.Collect();
What's different about namespace declaration
when comparing that to package declaration in Java?
No semicolon.
What's the difference between const and
readonly?
You can initialize readonly variables to some
runtime values. Let's say your program uses current date and time as one of the
values that won't change. This way you declare public readonly string DateT =
new DateTime().ToString().
What happens when you encounter a continue
statement inside the for loop?
The code for the rest of the loop is ignored, the
control is transferred back to the beginning of the loop.
What's the advantage of using
System.Text.StringBuilder over System.String?
StringBuilder is more efficient in the cases, where
a lot of manipulation is done to the text. Strings are immutable, so each time
it's being operated on, a new instance is created.
Can you store multiple data types in
System.Array?
No.
What's the difference between the
System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the
second one is shallow.
How can you sort the elements of the array in
descending order?
By calling Sort() and then Reverse() methods.
What's the .NET datatype that allows the
retrieval of data by a unique key?
HashTable.
What's class SortedList underneath?
A sorted HashTable.
Will finally block get executed if the
exception had not occurred?
Yes.
Can multiple catch blocks be executed?
No, once the proper catch code fires off, the
control is transferred to the finally block (if there are any), and then
whatever follows the finally block.
Why is it a bad idea to throw your own
exceptions?
Well, if at that point you know that an error has
occurred, then why not write the proper code to handle that error instead of
passing a new Exception object to the catch block? Throwing your own exceptions
signifies some design flaws in the project.
What's a delegate?
A delegate object encapsulates a reference to a
method. In C++ they were referred to as function pointers.
What's a multicast delegate?
It's a delegate that points to and eventually fires
off several methods.
How's the DLL Hell problem solved in .NET?
Assembly versioning allows the application to
specify not only the library it needs to run (which was available under Win32),
but also the version of the assembly.
What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY
command.
What's a satellite assembly?
When you write a multilingual or multi-cultural
application in .NET, and want to distribute the core application separately from
the localized modules, the localized assemblies that modify the core
application are called satellite assemblies.
What namespaces are necessary to create a
localized application?
System.Globalization, System.Resources.
What does assert() do?
In debug compilation, assert takes in a Boolean
condition as a parameter, and shows the error dialog if the condition is
false. The program proceeds without any interruption if the condition is
true.
What's the difference between the Debug class
and Trace class?
Documentation looks the same. Use Debug class for
debug builds, use Trace class for both debug and release builds.
Why are there five tracing levels in
System.Diagnostics.TraceSwitcher?
The tracing dumps can be quite verbose and for some
applications that are constantly running you run the risk of overloading the
machine and the hard drive there. Five levels range from None to Verbose,
allowing to fine-tune the tracing activities.
Where is the output of TextWriterTraceListener
redirected?
To the Console or a text file depending on the
parameter passed to the constructor.
What namespaces are necessary to create a
localized application?
System.Globalization, System.Resources.
What are three test cases you should go through in unit testing?
Positive test cases (correct data, correct output), negative test cases
(broken or missing data, proper handling), exception test
cases (exceptions are thrown and caught
properly).
Can you change the value of a variable while
debugging a C# application?
Yes, if you are debugging via Visual Studio.NET,
just go to Immediate window.
What's the implicit name of the parameter that
gets passed into the class' set method?
Value, and it's datatype depends on whatever
variable we're changing.
How do you inherit from a class in C#?
Place a colon and then the name of the base class.
Notice that it's double colon in C++.
Does C# support multiple inheritance?
No, use interfaces instead.
When you inherit a protected class-level
variable, who is it available to?
Derived Classes.
What's the top .NET class that everything is
derived from?
System.Object.
How's method overriding different from
overloading?
When overriding, you change the method behavior for
a derived class. Overloading simply involves having a method with the
same name within the class.
What does the keyword virtual mean in the
method definition?
The method can be over-ridden.
Can you declare the override method static
while the original method is non-static?
No, you can't, the signature of the virtual method
must remain the same, only the keyword virtual is changed to
keyword override.
Can you override private virtual methods?
No, moreover, you cannot access private methods in
inherited classes, have to be protected in the base class to allow any sort of
access.
Can you prevent your class from being
inherited and becoming a base class for some other classes?
Yes, that's what keyword sealed in the class
definition is for. The developer trying to derive from your class will get
a message: cannot inherit from Sealed class WhateverBaseClassName.
It's the same concept as final class in Java.
Can you allow class to be inherited, but
prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.
Why can't you specify the accessibility
modifier for methods inside the interface?
They all must be public. Therefore, to prevent you
from getting the false impression that you have any freedom of choice, you are
not allowed to specify any accessibility, it's public by default.
Can you inherit multiple interfaces?
Yes, why not.
And if they have conflicting method names?
It's up to you to implement the method inside your
own class, so implementation is left entirely up to you. This might cause a
problem on a higher-level scale if similarly named methods from different
interfaces expect different data, but as far as compiler cares you're
okay.
What's the difference between an interface and
abstract class?
In the interface all methods must be abstract, in
the abstract class some methods can be concrete. In the interface no
accessibility modifiers are allowed, which is ok in abstract classes.
How can you overload a method?
Different parameter data types, different number of
parameters, different order of parameters.
If a base class has a bunch of overloaded
constructors, and an inherited class has another bunch of overloaded
constructors, can you enforce a call from an inherited constructor to an
arbitrary base constructor?
Yes, just place a colon, and then keyword base
(parameter list to invoke the appropriate constructor) in the
overloaded constructor definition inside the inherited class.
What's the difference between System.String
and System.StringBuilder classes?
System.String is immutable, System.StringBuilder was
designed with the purpose of having a mutable string where a variety of
operations can be performed.
Does C# support multiple-inheritance?
No, use interfaces instead.
When you inherit a protected class-level
variable, who is it available to?
The derived class.
Are private class-level variables inherited?
Yes, but they are not accessible. Although they are not visible or
accessible via the class interface, they are inherited.
Describe the accessibility modifier
"protected internal".
It is available to derived classes and classes
within the same Assembly (and naturally from the base class it's declared in).
What's the top .NET class that everything is
derived from?
System.Object.
What's the advantage of using
System.Text.StringBuilder over System.String?
StringBuilder is more efficient in cases where there
is a large amount of string manipulation. Strings are immutable, so each
time it's being operated on, a new instance is created.
Can you store multiple data types in
System.Array?
No.
What's the .NET class that allows the
retrieval of a data element using a unique key?
HashTable.
Will the finally block get executed if an
exception has not occurred?
Yes.
What's an abstract class?
A class that cannot be instantiated. An
abstract class is a class that must be inherited and have the methods
overridden. An abstract class is essentially a blueprint for a class
without any implementation.
When do you absolutely have to declare a class as abstract?
1. When at least one of the
methods in the class is abstract.
2. When the class itself is inherited
from an abstract class, but not all base abstract methods have been overridden.
What's an interface?
It's an abstract class with public abstract methods all of which must be
implemented in the inherited classes.
Why can't you specify the accessibility
modifier for methods inside the interface?
They all must be public. Therefore, to prevent
you from getting the false impression that you have any freedom of choice,
you are not allowed to specify any
accessibility, it's public by default.
What's the difference between an interface and
abstract class?
In an interface class, all methods must be
abstract. In an abstract class some methods can be concrete. In an
interface class, no accessibility modifiers are allowed, which is ok in an
abstract class.
How is method overriding different from method
overloading?
When overriding a method, you change the behavior of
the method for the derived class. Overloading a method simply
involves
having another method with the same name
within the class.
Can you declare an override method to be
static if the original method is non-static?
No. The signature of the virtual method must remain
the same, only the keyword virtual is changed to keyword override.
Can you override private virtual methods?
No. Private methods are not accessible outside
the class.
Can you write a class without specifying
namespace? Which namespace does it belong to by default?
Yes, you can, then the class belongs to global
namespace which has no name. For commercial products, naturally, you
wouldn't want global namespace.
What is a formatter?
A formatter is an object that is responsible for
encoding and serializing data into messages on one end, and deserializing
and decoding messages into data on the other end.
Different b/w .NET & J2EE ?
Differences between J2EE and the .NET Platform
Vendor Neutrality
The .NET platform is not vendor neutral, it is tied
to the Microsoft operating systems. But neither are any of the J2EE
implementations
Many companies buy into J2EE believing that it will give them vendor
neutrality. And, in fact, this is a stated goal of Sun's vision:
A wide variety of J2EE product configurations and implementations, all of which
meet the requirements of this specification, are possible. A portable J2EE
application will function correctly when successfully deployed in any of these
products. (ref : Java 2 Platform Enterprise Edition Specification, v1.3, page
2-7 available at http://java.sun.com/j2ee/)
Overall Maturity
Given that the .NET platform has a three year lead
over J2EE, it should be no surprise to learn that the .NET platform is far more
mature than the J2EE platform. Whereas we have high volume highly reliable web
sites using .NET technologies (NASDAQ and Dell being among many examples)
Interoperability and Web Services
The .NET platform eCollaboration model is, as I have
discussed at length, based on the UDDI and SOAP standards. These standards are
widely supported by more than 100 companies. Microsoft, along with IBM and
Ariba, are the leaders in this area. Sun is a member of the UDDI consortium and
recognizes the importance of the UDDI standards. In a recent press release,
Sun's George Paolini, Vice President for the Java Community Development,
says:
"Sun has always worked to help establish and
support open, standards-based technologies that facilitate the growth of
network-based applications, and we see UDDI as an important project to
establish a registry framework for business-to-business e-commerce
But while Sun publicly says it believes in the UDDI
standards, in reality, Sun has done nothing whatsoever to incorporate any of
the UDDI standards into J2EE.
Scalability
Typical Comparision w.r.t Systems and their costs
J2EE
Company System Total
Sys.
Cost
Bull
Escala T610
c/s
16,785 $1,980,179
IBM RS/6000
Enterprise Server
F80
16,785 $2,026,681
Bull
Escala EPC810
c/s
33,375 $3,037,499
IBM RS/6000
Enterprise Server M80
33,375 $3,097,055
Bull
Escala
EPC2450
110,403 $9,563,263
IBM
IBM eServer pSeries 680 Model 7017-S85 110,403
$9,560,594
.NET platform systems
Company System Total
Sys.
Cost
Dell PowerEdge
4400
16,263 $273,487
Compaq
ProLiant
ML-570-6/700-3P 20,207
$201,717
Dell
PowerEdge
6400
30,231 $334,626
IBM
Netfinity 7600
c/s 32,377
$443,463
Compaq
ProLiant 8500-X550-64P 161,720
$3,534,272
Compaq
ProLiant
8500-X700-64P 179,658
$3,546,582
Compaq
ProLiant
8500-X550-96P 229,914
$5,305,571
Compaq
ProLiant 8500-X700-96P 262,244
$5,305,571
Compaq
ProLiant
8500-700-192P 505,303
$10,003,826
Framework Support
The .NET platform includes such an eCommerce
framework called Commerce Server. At this point, there is no equivalent
vendor-neutral framework in the J2EE space. With J2EE, you should assume that
you will be building your new eCommerce solution from scratch
Moreover, no matter what [J2EE] vendor you choose,
if you expect a component framework that will allow you to quickly field
complete e-business applications, you are in for a frustrating experience
Language
In the language arena, the choice is about as simple
as it gets. J2EE supports Java, and only Java. It will not support any other
language in the foreseeable future. The .NET platform supports every language
except Java (although it does support a language that is syntactically and
functionally equivalent to Java, C#). In fact, given the importance of the .NET
platform as a language independent vehicle, it is likely that any language that
comes out in the near future will include support for the .NET platform.
Some companies are under the impression that J2EE
supports other languages. Although both IBM's WebSphere and BEA's WebLogic
support other languages, neither does it through their J2EE technology. There
are only two official ways in the J2EE platform to access other languages, one
through the Java Native Interface and the other through CORBA interoperability.
Sun recommends the later approach. As Sun's Distinguished Scientist and Java
Architect Rick Cattell said in a recent interview.
Portability
The reason that operating system portability is a
possibility with J2EE is not so much because of any inherent portability of
J2EE, as it is that most of the J2EE vendors support multiple operating
systems. Therefore as long as one sticks with a given J2EE vendor and a given
database vendor, moving from one operating system to another should be
possible. This is probably the single most important benefit in favor of J2EE
over the .NET platform, which is limited to the Windows operating system. It is
worth noting, however, that Microsoft has submitted the specifications for C#
and a subset of the .NET Framework (called the common language infrastructure)
to ECMA, the group that standardizes JavaScript.
J2EE offers an acceptable solution to ISVs when the
product must be marketed to non-Windows customers, particularly when the J2EE
platform itself can be bundled with the ISV's product as an integrated
offering.
If the primary customer base for the ISV is Windows
customers, then the .NET platform should be chosen. It will provide
much better performance at a much lower cost.
Client device independence
The major difference being that with Java, it is the
presentation tier programmer that determines the ultimate HTML that will be
delivered to the client, and with .NET, it is a Visual Studio.NET control.
This Java approach has three problems. First, it
requires a lot of code on the presentation tier, since every possible thin
client system requires a different code path. Second, it is very difficult to
test the code with every possible thin client system. Third, it is very
difficult to add new thin clients to an existing application, since to do so involves
searching through, and modifying a tremendous amount of presentation tier
logic.
The .NET Framework approach is to write device
independent code that interacts with visual controls. It is the control, not
the programmer, that is responsible for determining what HTML to deliver, based
on the capabilities of the client device.. In the .NET Framework model, one can
forget that such a thing as HTML even exists! Contd ....
Conclusion
Sun's J2EE vision is based on a family of
specifications that can be implemented by many vendors. It is open in the sense
that any company can license and implement the technology, but closed in the
sense that it is controlled by a single vendor, and a self contained
architectural island with very limited ability to interact outside of itself.
One of J2EE's major disadvantages is that the choice of the platform dictates
the use of a single programming language, and a programming language that is
not well suited for most businesses. One of J2EE's major advantages is that
most of the J2EE vendors do offer operating system portability.
Microsoft's .NET platform vision is a family of
products rather than specifications, with specifications used primarily to
define points of interoperability. The major disadvantage of this approach is
that if is limited to the Windows platform, so applications written for the
.NET platform can only be run on .NET platforms. Their are several important
advantages to the .NET platform:
* The cost of developing applications is much lower,
since standard business languages can be used and device independent
presentation tier logic can be written.
* The cost of running applications is much lower,
since commodity hardware platforms (at 1/5 the cost of their Unix counterparts)
can be used.
* The ability to scale up is much greater, with the
proved ability to support at least ten times the number of clients any J2EE
platform has shown itself able to support.
* Interoperability is much stronger, with industry
standard eCollaboration built into the platform.
What are the Main Features of .NET platform?
Features of .NET Platform are :-
Common Language Runtime
Explains the features and benefits of the common language runtime, a run-time
environment that manages the execution of code and provides services that simplify
the development process.
Assemblies
Defines the concept of assemblies, which are collections of types and resources
that form logical units of functionality. Assemblies are the fundamental units
of deployment, version control, reuse, activation scoping, and security
permissions.
Application Domains
Explains how to use application domains to provide isolation between
applications.
Runtime Hosts
Describes the runtime hosts supported by the .NET Framework, including ASP.NET,
Internet Explorer, and shell executables.
Common Type System
Identifies the types supported by the common language runtime.
Metadata and Self-Describing Components
Explains how the .NET Framework simplifies component interoperation by allowing
compilers to emit additional declarative information, or metadata, into all
modules and assemblies.
Cross-Language Interoperability
Explains how managed objects created in different programming languages can
interact with one another.
.NET Framework Security
Describes mechanisms for protecting resources and code from unauthorized code
and unauthorized users.
.NET Framework Class Library
Introduces the library of types provided by the .NET Framework, which expedites
and optimizes the development process and gives you access to system functionality.
What is the use of JIT ?
JIT (Just - In - Time) is a compiler which converts MSIL code to Native Code
(ie.. CPU-specific code that runs on the same computer architecture).
Because the common language runtime supplies a JIT
compiler for each supported CPU architecture, developers can write a set of
MSIL that can be JIT-compiled and run on computers with different
architectures. However, your managed code will run only on a specific operating
system if it calls platform-specific native APIs, or a platform-specific class
library.
JIT compilation takes into account the fact that
some code might never get called during execution. Rather than using time and
memory to convert all the MSIL in a portable executable (PE) file to native
code, it converts the MSIL as needed during execution and stores the resulting
native code so that it is accessible for subsequent calls. The loader creates
and attaches a stub to each of a type's methods when the type is loaded. On the
initial call to the method, the stub passes control to the JIT compiler, which
converts the MSIL for that method into native code and modifies the stub to
direct execution to the location of the native code. Subsequent calls of the
JIT-compiled method proceed directly to the native code that was previously
generated, reducing the time it takes to JIT-compile and run the code.
What meant of assembly & global assembly cache
(gac) & Meta data.
Assembly :-- An assembly is the primary building block of a .NET based
application. It is a collection of functionality that is built, versioned, and
deployed as a single implementation unit (as one or more files). All managed
types and resources are marked either as accessible only within their
implementation unit, or as accessible by code outside that unit. It overcomes
the problem of 'dll Hell'.The .NET Framework uses assemblies as the fundamental
unit for several purposes:
- Security
- Type
Identity
- Reference
Scope
- Versioning
- Deployment
Global Assembly Cache :-- Assemblies can be shared
among multiple applications on the machine by registering them in global
Assembly cache(GAC). GAC is a machine wide a local cache of assemblies
maintained by the .NET Framework. We can register the assembly to global
assembly cache by using gacutil command.
We can Navigate to the GAC directory, C:\winnt\Assembly in explore. In the
tools menu select the cache properties; in the windows displayed you can set
the memory limit in MB used by the GAC
MetaData :--Assemblies have Manifests. This Manifest contains Metadata
information of the Module/Assembly as well as it contains detailed Metadata of
other assemblies/modules references (exported). It's the Assembly Manifest
which differentiates between an Assembly and a Module.
What are the mobile devices supported by .net
platform
The Microsoft .NET Compact Framework is designed to
run on mobile devices such as mobile phones, Personal Digital Assistants
(PDAs), and embedded devices. The easiest way to develop and test a Smart
Device Application is to use an emulator.
These devices are divided into two main divisions:
1) Those that are directly supported by .NET (Pocket PCs, i-Mode phones, and
WAP devices)
2) Those that are not (Palm OS and J2ME-powered devices).
What is GUID , why we use it and where?
GUID :-- GUID is Short form of Globally Unique Identifier, a unique 128-bit
number that is produced by the Windows OS or by some Windows applications to
identify a particular component, application, file, database entry, and/or
user. For instance, a Web site may generate a GUID and assign it to a user's
browser to record and track the session. A GUID is also used in a Windows
registry to identify COM DLLs. Knowing where to look in the registry and having
the correct GUID yields a lot information about a COM object (i.e., information
in the type library, its physical location, etc.). Windows also identifies user
accounts by a username (computer/domain and username) and assigns it a GUID.
Some database administrators even will use GUIDs as primary key values in
databases.
GUIDs can be created in a number of ways, but
usually they are a combination of a few unique settings based on specific point
in time (e.g., an IP address, network MAC address, clock date/time, etc.).
Describe the difference between inline and code
behind - which is best in a loosely coupled solution
ASP.NET supports two modes of page development: Page
logic code that is written inside runat="server"> blocks within an
.aspx file and dynamically compiled the first time the page is requested on the
server. Page logic code that is written within an external class that is
compiled prior to deployment on a server and linked
""behind"" the .aspx file at run time.
Whats MSIL, and why should my developers need an
appreciation of it if at all?
When compiling the source code to managed code, the compiler translates the
source into Microsoft intermediate language (MSIL). This is a CPU-independent
set of instructions that can efficiently be converted to native code. Microsoft
intermediate language (MSIL) is a translation used as the output of a number of
compilers. It is the input to a just-in-time (JIT) compiler. The Common
Language Runtime includes a JIT compiler for the conversion of MSIL to native
code.
Before Microsoft Intermediate Language (MSIL) can be
executed it, must be converted by the .NET Framework just-in-time (JIT)
compiler to native code. This is CPU-specific code that runs on the same
computer architecture as the JIT compiler. Rather than using time and memory to
convert all of the MSIL in a portable executable (PE) file to native code. It
converts the MSIL as needed whilst executing, then caches the resulting native
code so its accessible for any subsequent calls.
How many .NET languages can a single .NET DLL
contain?
One
What type of code (server or client) is found in a
Code-Behind class?
Server
Whats an assembly?
Assemblies are the building blocks of .NET Framework
applications; they form the fundamental unit of deployment, version control,
reuse, activation scoping, and security permissions. An assembly is a
collection of types and resources that are built to work together and form a
logical unit of functionality. An assembly provides the common language runtime
with the information it needs to be aware of type implementations. To the
runtime, a type does not exist outside the context of an assembly.
How many classes can a single .NET DLL contain?
Unlimited.
What is the difference between string and String ?
No difference
What is manifest?
It is the metadata that describes the assemblies.
What is metadata?
Metadata is machine-readable information about a resource, or ""data
about data."" Such information might include details on content,
format, size, or other characteristics of a data
source. In .NET, metadata includes type definitions, version information,
external assembly references, and other standardized information.
What are the types of assemblies?
There are four types of assemblies in .NET:
Static assemblies
These are the .NET PE files that you create at compile time.
Dynamic assemblies
These are PE-formatted, in-memory assemblies that you dynamically create at
runtime using the classes in the System.Reflection.Emit namespace.
Private assemblies
These are static assemblies used by a specific application.
Public or shared assemblies
These are static assemblies that must have a unique shared name and can be used
by any application.
An application uses a private assembly by referring
to the assembly using a static path or through an XML-based application
configuration file. While the CLR doesn't enforce versioning policies-checking
whether the correct version is used-for private assemblies, it ensures that an
application uses the correct shared assemblies with which the application was
built. Thus, an application uses a specific shared assembly by referring to the
specific shared assembly, and the CLR ensures that the correct version is
loaded at runtime.
In .NET, an assembly is the smallest unit to which
you can associate a version number;
What are delegates?where are they used ?
A delegate defines a reference type that can be used
to encapsulate a method with a specific signature. A delegate instance
encapsulates a static or an instance method. Delegates are roughly similar to
function pointers in C++; however, delegates are type-safe and secure.
When do you use virutal keyword?.
When we need to override a method of the base class in the sub class, then we
give the virtual keyword in the base class method. This makes the method in the
base class to be overridable. Methods, properties, and indexers can be virtual,
which means that their implementation can be overridden in derived classes.
What are class access modifiers ?
Access modifiers are keywords used to specify the declared accessibility of a
member or a type. This section introduces the four access modifiers:
· Public - Access is not restricted.
· Protected - Access is limited to the containing class or types derived
from the containing class.
· Internal - Access is limited to the current assembly.
· Protected inertnal - Access is limited to the current assembly or types
derived · from the containing class.
· Private - Access is limited to the containing type.
What Is Boxing And Unboxing?
Boxing :- Boxing is an implicit conversion of a
value type to the type object type
Eg:-
Consider the following declaration of a value-type variable:
int i = 123;
object o = (object) i;
Boxing Conversion
UnBoxing :- Unboxing is an explicit conversion from
the type object to a value type
Eg:
int i = 123; // A value
type
object box = i; // Boxing
int j = (int)box; // Unboxing
What is Value type and refernce type in .Net?.
Value Type : A variable of a value type always
contains a value of that type. The assignment to a variable of a value type
creates a copy of the assigned value, while the assignment to a variable of a
reference type creates a copy of the reference but not of the referenced
object.
The value types consist of two main categories:
* Stuct Type
* Enumeration Type
Reference Type :Variables of reference types,
referred to as objects, store references to the actual data. This section
introduces the following keywords used to declare reference types:
* Class
* Interface
* Delegate
This section also introduces the following built-in
reference types:
* object
* string
What is the difference between structures and
enumeration?.
Unlike classes, structs are value types and do not
require heap allocation. A variable of a struct type directly contains the data
of the struct, whereas a variable of a class type contains a reference to the
data. They are derived from System.ValueType class.
Enum->An enum type is a distinct type that
declares a set of named constants.They are strongly typed constants. They
are unique types that allow to declare symbolic names to integral values. Enums
are value types, which means they contain their own value, can't inherit or be
inherited from and assignment copies the value of one enum to another.
public enum Grade
{
A,
B,
C
}
What is namespaces?.
Namespace is a logical naming scheme for group related types.Some class types
that logically belong together they can be put into a common namespace. They
prevent namespace collisions and they provide scoping. They are imported as
"using" in C# or "Imports" in Visual Basic. It seems as if
these directives specify a particular assembly, but they don't. A namespace can
span multiple assemblies, and an assembly can define multiple namespaces. When
the compiler needs the definition for a class type, it tracks through
each of the different imported namespaces to the type name and searches each
referenced assembly until it is found.
Namespaces can be nested. This is very similar to packages in Java as far as
scoping is concerned.
How do you create shared assemblies?.
Just look through the definition of Assemblies..
* An Assembly is a logical unit of code
* Assembly physically exist as DLLs or EXEs
* One assembly can contain one or more files
* The constituent files can include any file types like image
files, text files etc. along with DLLs or EXEs
* When you compile your source code by default the exe/dll
generated is actually an assembly
* Unless your code is bundled as assembly it can not be used in
any other application
* When you talk about version of a component you are actually
talking about version of the assembly to which the component belongs.
* Every assembly file contains information about itself. This
information is called as Assembly Manifest.
Following steps are involved in creating shared
assemblies :
* Create your DLL/EXE source code
* Generate unique assembly name using SN utility
* Sign your DLL/EXE with the private key by modifying AssemblyInfo
file
* Compile your DLL/EXE
* Place the resultant DLL/EXE in global assembly cache using AL
utility
What is global assembly cache?
Each computer where the common language runtime is
installed has a machine-wide code cache called the global assembly cache. The
global assembly cache stores assemblies specifically designated to be shared by
several applications on the computer.
There are several ways to deploy an assembly into the global assembly
cache:
· Use an installer designed to work with the global assembly cache. This is the
preferred option for installing assemblies into the global assembly cache.
· Use a developer tool called the Global Assembly Cache tool (Gacutil.exe),
provided by the .NET Framework SDK.
· Use Windows Explorer to drag assemblies into the cache.
What is MSIL?.
When compiling to managed code, the compiler translates your source code into
Microsoft intermediate language (MSIL), which is a CPU-independent set of
instructions that can be efficiently converted to native code. MSIL includes
instructions for loading, storing, initializing, and calling methods on
objects, as well as instructions for arithmetic and logical operations, control
flow, direct memory access, exception handling, and other operations. Before
code can be run, MSIL must be converted to CPU-specific code, usually by a
just-in-time (JIT) compiler. Because the common language runtime supplies one
or more JIT compilers for each computer architecture it supports, the same set
of MSIL can be JIT-compiled and run on any supported architecture.
When a compiler produces MSIL, it also produces metadata. Metadata describes
the types in your code, including the definition of each type, the signatures
of each type's members, the members that your code references, and other data
that the runtime uses at execution time. The MSIL and metadata are contained in
a portable executable (PE) file that is based on and extends the published
Microsoft PE and common object file format (COFF) used historically for
executable content. This file format, which accommodates MSIL or native code as
well as metadata, enables the operating system to recognize common language
runtime images. The presence of metadata in the file along with the MSIL
enables your code to describe itself, which means that there is no need for
type libraries or Interface Definition Language (IDL). The runtime locates and
extracts the metadata from the file as needed during execution.
What is Jit compilers?.how many are available in
clr?
Just-In-Time compiler- it converts the language that you write in .Net into
machine language that a computer can understand. there are tqo types of JITs
one is memory optimized & other is performace optimized.
What is tracing?Where it used.Explain few methods
available
Tracing refers to collecting information about the
application while it is running. You use tracing information to
troubleshoot an application.
Tracing allows us to observe and correct programming errors. Tracing enables
you to record information in various log files about the errors that might
occur at run time. You can analyze these log files to find the cause of the
errors.
In .NET we have objects called Trace Listeners. A
listener is an object that receives the trace output and outputs it somewhere;
that somewhere could be a window in your development environment, a file on
your hard drive, a Windows Event log, a SQL Server or Oracle database, or any
other customized data store.
The System.Diagnostics namespace provides the
interfaces, classes, enumerations and structures that are used for tracing The
System.Diagnostics namespace provides two classes named Trace and Debug that
are used for writing errors and application execution information in logs.
All Trace Listeners have the following functions.
Functionality of these functions is same except that the target media for the
tracing output is determined by the Trace Listener.
Method Name
Result Fail Outputs the specified text with the Call Stack.
Write Outputs the specified text.
WriteLine Outputs the specified text and a carriage return.
Flush Flushes the output buffer to the target media.
Close Closes the output stream in order to not receive the
tracing/debugging output
How to set the debug mode?
Debug Mode for ASP.NET applications - To set ASP.NET
appplication in debugging mode, edit the application's web.config and assign
the "debug" attribute in < compilation > section to "true"
as show below:
< configuration >
< system.web >
< compilation defaultLanguage="vb"
debug="true" / >
....
...
..
< / configuration >
This case-sensitive attribute 'debug tells ASP.NET
to generate symbols for dynamically generated files and enables the
debugger to attach to the ASP.NET application. ASP.NET will detect this change
automatically, without the need to restart the server. Debug Mode for ASP.NET
Webservices - Debugging an XML Web service created with ASP.NET is similar to
the debugging an ASP.NET Web application.
What is the property available to check if the page
posted or not?
The Page_Load event handler in the page checks for
IsPostBack property value, to ascertain whether the page is posted. The
Page.IsPostBack gets a value indicating whether the page is being loaded in
response to the client postback, or it is for the first time. The value of
Page.IsPostBack is True, if the page is being loaded in response to the client
postback; while its value is False, when the page is loaded for the first time.
The Page.IsPostBack property facilitates execution of certain routine in
Page_Load, only once (for e.g. in Page load, we need to set default value in
controls, when page is loaded for the first time. On post back, we check for
true value for IsPostback value and then invoke server-side code to
update data).
Which are the abstract classes available under
system.xml namespace?
The System.XML namespace provides XML related processing ability in .NET
framework. XmlReader and XMLWriter are the two abstract classes at the core of
.NET Framework XML classes:
1. XmlReader provides a fast, forward-only,
read-only cursor for processing an XML document stream.
2. XmlWriter provides an interface for producing XML document streams that
conform to the W3C's XML standards.
Both XmlReader and XmlWriter are abstract base
classes, which define the functionality that all derived classes must support.
Is it possible to use multipe inheritance in .net?
Multiple Inheritance is an ability to inherit from more than one base class
i.e. ability of a class to have more than one superclass, by inheriting
from different sources and thus combine separately-defined behaviors in a
single class. There are two types of multiple inheritance: multiple
type/interface inheritance and multiple implementation inheritance. C# &
VB.NET supports only multiple type/interface inheritance, i.e.
you can derive an class/interface from multiple interfaces. There is no support
for multiple implementation inheritance in .NET. That means a class can only
derived from one class.
What are the derived classes from xmlReader and
xmlWriter?
Both XmlReader and XmlWriter are abstract base
classes, which define the functionality that all derived classes must support.
There are three concrete implementations of XmlReader:
1.XmlTextReader
2.XmlNodeReader
3.XmlValidatingReader
There are two concrete implementations of XmlWriter:
1.XmlTextWriter
2.XmlNodeWriter
XmlTextReader and XmlTextWriter support reading data to/from text-based stream,
while XmlNodeReader and XmlNodeWriter are designed for working with in-memory
DOM tree structure. The custom readers and writers can also be developed to
extend the built-in functionality of XmlReader and XmlWriter.
What is managed and unmanaged code?
The .NET framework provides several core run-time
services to the programs that run within it - for example exception handling
and security. For these services to work, the code must provide a minimum level
of information to the runtime. i.e., code executing under the control of the
CLR is called managed code. For example, any code written in C# or Visual Basic
.NET is managed code.
Code that runs outside the CLR is referred to as
"unmanaged code." COM components, ActiveX components, and Win32 API
functions are examples of unmanaged code.
How you deploy .NET assemblies?
One way is simply use xcopy. others are use and the
setup projects in .net. and one more way is use of nontuch deployment.
What is Globalizationa and Localization ?
Globalization is the process of creating an
application that meets the needs of users from multiple cultures. It includes
using the correct
currency, date and time format, calendar, writing direction, sorting rules, and
other issues. Accommodating these cultural differences in an application is
called localization.Using classes of System.Globalization namespace, you can
set application's current culture.
This can be achieved by using any of the following 3
approaches.
1. Detect and
redirect
2. Run-time
adjustment
3. Using Satellite
assemblies.
Whate are Resource Files ? How are they used in .NET?
Resource files are the files containing data that is logically deployed
with an application.These files can contain data in a number of formats
including strings, images and persisted objects. It has the main advantage of
If we store data in these files then we don't need to compile these if the data
get changed. In .NET we basically require them storing culture specific
informations by localizing application's resources. You can deploy your
resources using satellite assemblies.
Difference between Dispose and Finallize method?
Finalize method is used to free the memory used by some unmanaged resources
like window handles (HWND). It's similar to the destructor syntax in C#. The GC
calls this method when it founds no more references to the object. But, In some
cases we may need release the memory used by the resources explicitely.To
release the memory explicitly we need to implement the Dispose method of
IDisposable interface.
What is encapsulation ?
Encapsulation is the ability to hide the internal
workings of an object's behavior and its data. For instance, let's say you have
a object named Bike and this object has a method named start(). When you create
an instance of a Bike object and call its start() method you are not worried
about what happens to accomplish this, you just want to make sure the state of
the bike is changed to 'running' afterwards. This kind of behavior hiding is
encapsulation and it makes programming much easier.
How can you prevent your class to be inherated
further?
By setting Sealed - Key word
public sealed class Planet
{
//code
goes here
}
class Moon:Planet
{
//Not allowed as base class is sealed
}
What is GUID and why we need to use it and in what condition? How this
is created.
A GUID is a 128-bit integer (16 bytes) that can be used across all
computers and networks wherever a unique identifier is required. Such an
identifier has a very low probability of being duplicated. Visual Studio .NET
IDE has a utility under the tools menu to generate GUIDs.
Why do you need to serialize.?
We need to serialize the object,if you want to pass object from one
computer/application domain to another.Process of converting complex objects
into stream of bytes that can be persisted or transported.Namespace for
serialization is System.Runtime.Serialization.The ISerializable interface
allows you to make any class Serializable..NET framework features 2 serializing
method.
1.Binary Serialization 2.XML Serialization
What is inline schema, how does it works?
Schemas can be included inside of XML file is called
Inline Schemas.This is useful when it is inconvenient to physically
seprate the schema and the XML document.A schema is an XML document that
defines the structure, constraints, data types, and relationships of the
elements that constitute the data contained inside the XML document or in
another XML document.Schema can be an external file which uses the XSD or
XDR extension called external schema. Inline schema can take place even when
validation is turned off.
Describe the advantages of writing a managed code
application instead of unmanaged one. What's involved in certain piece of code
being managed?
"Advantage includes automatic garbage
collection,memory management,security,type checking,versioning
Managed code is compiled for the .NET run-time
environment. It runs in the Common Language Runtime (CLR), which is the heart
of the .NET Framework. The CLR provides services such as security,
memory management, and cross-language integration. Managed applications written
to take advantage of the features of the CLR perform more efficiently and
safely, and take better advantage of developers existing expertise in languages
that support the .NET Framework.
Unmanaged code includes all code written before the
.NET Framework was introduced—this includes code written to use COM, native
Win32, and Visual Basic 6. Because it does not run inside the .NET environment,
unmanaged code cannot make use of any .NET managed facilities."
What are multicast delegates ? give me an example ?
Delegate that can have more than one element in its
invocation List.
using System;
namespace SampleMultiCastDelegate
{
class MultiCast
{
public delegate string strMultiCast(string s);
}
}
MainClass defines the static methods having same signature as delegate.
using System;
namespace SampleMultiCastDelegate
{
public class MainClass
{
public MainClass()
{
}
public static string Jump(string
s)
{
Console.WriteLine("Jump");
return String.Empty;
}
public static string Run(string
s)
{
Console.WriteLine("Run");
return String.Empty;
}
public static string Walk(string
s)
{
Console.WriteLine("Walk");
return
String.Empty;
}
}
}
The Main class:
using System;
using System.Threading;
namespace SampleMultiCastDelegate
{
public class MainMultiCastDelegate
{
public static void Main()
{
MultiCast.strMultiCast Run,Walk,Jump;
MultiCast.strMultiCast myDelegate;
///here
mydelegate used the Combine method of System.MulticastDelegate
///and the delegates combine
myDelegate=(MultiCast.strMultiCast)System.Delegate.Combine(Run,Walk);
}
}
}
Can a nested object be used in Serialization ?
Yes. If a class that is to be serialized contains references to objects of
other classes, and if those classes have been marked as serializable, then
their objects are serialized too.
Difference between int and int32 ?
Both are same. System.Int32 is a .NET class. Int is
an alias name for System.Int32.
Describe the difference between a Thread and a
Process?
A Process is an instance of an running application.
And a thread is the Execution stream of the Process. A process can have
multiple Thread.
When a process starts a specific memory area is allocated to it. When there is
multiple thread in a process, each thread gets a memory for storing the
variables in it and plus they can access to the global variables which is
common for all the thread. Eg.A Microsoft Word is a Application. When you open
a word file,an instance of the Word starts and a process is allocated to this
instance which has one thread.
What is the difference between an EXE and a DLL?
You can create an objects of Dll but not of the EXE.
Dll is an In-Process Component whereas EXE is an OUt-Process Component.
Exe is for single use whereas you can use Dll for multiple use.
Exe can be started as standalone where dll cannot be.
What is strong-typing versus weak-typing? Which is
preferred? Why?
Strong typing implies that the types of variables
involved in operations are associated to the variable, checked at compile-time,
and require explicit conversion; weak typing implies that they are associated
to the value, checked at run-time, and are implicitly converted as required.
(Which is preferred is a disputable point, but I personally prefer strong
typing because I like my errors to be found as soon as possible.)
What is a PID? How is it useful when troubleshooting
a system?
PID is the process Id of the application in Windows. Whenever a process starts
running in the Windows environment, it is associated with an individual process
Id or PID.
The PID (Process ID) a unique number for each item
on the Process Tab, Image Name list. How do you get the PID to appear? In Task
Manger, select the View menu, then select columns and check PID (Process
Identifier).
In Linux, PID is used to debug a process explicitly.
However we cannot do this in a windows environment.
Microsoft has launched a SDK called as Microsoft
Operations Management (MOM). This uses the PID to find out which dll’s have
been loaded by a process in the memory. This is essentially helpful in
situations where the Process which has a memory leak is to be traced to a
erring dll. Personally I have never used a PID, our Windows debugger does the
things required to find out.
What is the GAC? What problem does it solve?
Each computer where the common language runtime is
installed has a machine-wide code cache called the global assembly cache. The
global assembly cache stores assemblies that are to be shared by several
applications on the computer. This area is typically the folder under windows
or winnt in the machine.
All the assemblies that need to be shared across
applications need to be done through the Global assembly Cache only. However it
is not necessary to install assemblies into the global assembly cache to make
them accessible to COM interop or unmanaged code.
There are several ways to deploy an assembly into
the global assembly cache:
· Use an installer designed to work with the global assembly cache. This is the
preferred option for installing assemblies into the global assembly cache.
· Use a developer tool called the Global Assembly Cache tool (Gacutil.exe),
provided by the .NET Framework SDK.
· Use Windows Explorer to drag assemblies into the cache.
GAC solves the problem of DLL Hell and DLL
versioning. Unlike earlier situations, GAC can hold two assemblies of the same
name but different version. This ensures that the applications which access a
particular assembly continue to access the same assembly even if another
version of that assembly is installed on that machine.
Describe what an Interface is and how it’s different
from a Class.
An interface is a structure of code which is similar
to a class. An interface is a prototype for a class and is useful from a
logical design perspective. Interfaces provide a means to define the protocols
for a class without worrying about the implementation details. The syntax for
creating interfaces follows:
interface Identifier {
InterfaceBody
}
Identifier is the name of the interface and
InterfaceBody refers to the abstract methods and static final variables that
make up the interface. Because it is assumed that all the methods in an
interface are abstract, it isn't necessary to use the abstract keyword
An interface is a description of some of the members
available from a class. In practice, the syntax typically looks similar to a
class definition, except that there's no code defined for the methods — just
their name, the arguments passed and the type of the value returned.
So what good is it? None by itself. But you create an interface so that classes
will implement it.
But what does it mean to implement an interface. The
interface acts as a contract or promise. If a class implements an interface,
then it must have the properties and methods of the interface defined in the
class. This is enforced by the compiler.
Broadly the differentiators between classes and
interfaces is as follows
• Interface should not have any implementation.
• Interface can not create any instance.
• Interface should provide high level abstraction from the implementation.
• Interface can have multiple inheritances.
• Default access level of the interface is public.
What is the difference between XML Web Services
using ASMX and .NET Remoting using SOAP?
ASP.NET Web services and .NET Remoting provide a
full suite of design options for cross-process and cross-plaform communication
in distributed applications. In general, ASP.NET Web services provide the
highest levels of interoperability with full support for WSDL and SOAP over
HTTP, while .NET Remoting is designed for common language runtime type-system
fidelity and supports additional data format and communication channels. Hence
if we looking cross-platform communication than web services is the choice coz
for .NET remoting .Net framework is requried which may or may not present for the
other platform.
Serialization and Metadata
ASP.NET Web services rely on the System.Xml.Serialization.XmlSerializer class
to marshal data to and from SOAP messages at runtime. For metadata, they
generate WSDL and XSD definitions that describe what their messages contain.
The reliance on pure WSDL and XSD makes ASP.NET Web services metadata portable;
it expresses data structures in a way that other Web service toolkits on
different platforms and with different programming models can understand. In
some cases, this imposes constraints on the types you can expose from a Web
service—XmlSerializer will only marshal things that can be expressed in XSD.
Specifically, XmlSerializer will not marshal object graphs and it has limited
support for container types.
.NET Remoting relies on the pluggable
implementations of the IFormatter interface used by the
System.Runtime.Serialization engine to marshal data to and from messages. There
are two standard formatters,
System.Runtime.Serialization.Formatters.Binary.BinaryFormatter and
System.Runtime.Serialization.Formatters.Soap.SoapFormatter. The BinaryFormatter
and SoapFormatter, as the names suggest, marshal types in binary and SOAP
format respectively. For metadata, .NET Remoting relies on the common language
runtime assemblies, which contain all the relevant information about the data
types they implement, and expose it via reflection. The reliance on the
assemblies for metadata makes it easy to preserve the full runtime type-system
fidelity. As a result, when the .NET Remoting plumbing marshals data, it
includes all of a class's public and private members; handles object graphs
correctly; and supports all container types (e.g.,
System.Collections.Hashtable). However, the reliance on runtime metadata also
limits the reach of a .NET Remoting system—a client has to understand .NET
constructs in order to communicate with a .NET Remoting endpoint. In addition
to pluggable formatters, the .NET Remoting layer supports pluggable channels,
which abstract away the details of how messages are sent. There are two
standard channels, one for raw TCP and one for HTTP. Messages can be sent over
either channel independent of format.
Distributed Application Design: ASP.NET Web Services
vs. .NET Remoting
ASP.NET Web services favor the XML Schema type system, and provide a simple
programming model with broad cross-platform reach. .NET Remoting favors the
runtime type system, and provides a more complex programming model with much
more limited reach. This essential difference is the primary factor in
determining which technology to use. However, there are a wide range of other
design factors, including transport protocols, host processes, security,
performance, state management, and support for transactions to consider as
well.
Security
Since ASP.NET Web services rely on HTTP, they integrate with the standard
Internet security infrastructure. ASP.NET leverages the security features
available with IIS to provide strong support for standard HTTP authentication
schemes including Basic, Digest, digital certificates, and even Microsoft® .NET
Passport. (You can also use Windows Integrated authentication, but only for
clients in a trusted domain.) One advantage of using the available HTTP
authentication schemes is that no code change is required in a Web service; IIS
performs authentication before the ASP.NET Web services are called. ASP.NET
also provides support for .NET Passport-based authentication and other custom
authentication schemes. ASP.NET supports access control based on target URLs,
and by integrating with the .NET code access security (CAS) infrastructure. SSL
can be used to ensure private communication over the wire.
Although these standard transport-level techniques
to secure Web services are quite effective, they only go so far. In complex
scenarios involving multiple Web services in different trust domains, you have
to build custom ad hoc solutions. Microsoft and others are working on a set of
security specifications that build on the extensibility of SOAP messages to
offer message-level security capabilities. One of these is the XML Web Services
Security Language (WS-Security), which defines a framework for message-level
credential transfer, message integrity, and message confidentiality.
As noted in the previous section, the .NET Remoting
plumbing does not secure cross-process invocations in the general case. A .NET
Remoting endpoint hosted in IIS with ASP.NET can leverage all the same security
features available to ASP.NET Web services, including support for secure
communication over the wire using SSL. If you are using the TCP channel or the
HTTP channel hosted in processes other than aspnet_wp.exe, you have to
implement authentication, authorization and privacy mechanisms yourself.
One additional security concern is the ability to
execute code from a semi-trusted environment without having to change the
default security policy. ASP.NET Web Services client proxies work in these
environments, but .NET Remoting proxies do not. In order to use a .NET Remoting
proxy from a semi-trusted environment, you need a special serialization
permission that is not given to code loaded from your intranet or the Internet
by default. If you want to use a .NET Remoting client from within a
semi-trusted environment, you have to alter the default security policy for
code loaded from those zones. In situations where you are connecting to systems
from clients running in a sandbox—like a downloaded Windows Forms application,
for instance—ASP.NET Web Services are a simpler choice because security policy
changes are not required.
Conceptually, what is the difference between
early-binding and late-binding?
Early binding – Binding at Compile Time
Late Binding – Binding at Run Time
Early binding implies that the class of the called
object is known at compile-time; late-binding implies that the class is not
known until run-time, such as a call through an interface or via Reflection.
Early binding is the preferred method. It is the
best performer because your application binds directly to the address of the
function being called and there is no extra overhead in doing a run-time
lookup. In terms of overall execution speed, it is at least twice as fast as
late binding.
Early binding also provides type safety. When you
have a reference set to the component's type library, Visual Basic provides
IntelliSense support to help you code each function correctly. Visual Basic
also warns you if the data type of a parameter or return value is incorrect,
saving a lot of time when writing and debugging code.
Late binding is still useful in situations where the
exact interface of an object is not known at design-time. If your application
seeks to talk with multiple unknown servers or needs to invoke functions by
name (using the Visual Basic 6.0 CallByName function for example) then you need
to use late binding. Late binding is also useful to work around compatibility
problems between multiple versions of a component that has improperly modified
or adapted its interface between versions.
What is an Asssembly Qualified Name? Is it a
filename? How is it different?
An assembly qualified name isn't the filename of the assembly; it's the
internal name of the assembly combined with the assembly version, culture, and
public key, thus making it unique.
e.g. (""System.Xml.XmlDocument,
System.Xml, Version=1.0.3300.0, Culture=neutral,
PublicKeyToken=b77a5c561934e089"")
How is a strongly-named assembly different from one
that isn’t strongly-named?
Strong names are used to enable the stricter naming
requirements associated with shared assemblies. These strong names are created
by a .NET utility – sn.exe
Strong names have three goals:
· Name uniqueness. Shared assemblies must have names that are globally unique.
· Prevent name spoofing. Developers don't want someone else releasing a
subsequent version of one of your assemblies and falsely claim it came from
you, either by accident or intentionally.
· Provide identity on reference. When resolving a reference to an assembly,
strong names are used to guarantee the assembly that is loaded came from the
expected publisher.
Strong names are implemented using standard public
key cryptography. In general, the process works as follows: The author of an
assembly generates a key pair (or uses an existing one), signs the file
containing the manifest with the private key, and makes the public key
available to callers. When references are made to the assembly, the caller
records the public key corresponding to the private key used to generate the
strong name.
Weak named assemblies are not suitable to be added
in GAC and shared. It is essential for an assembly to be strong named.
Strong naming prevents tampering and enables
assemblies to be placed in the GAC alongside other assemblies of the same name.
How does the generational garbage collector in the
.NET CLR manage object lifetime? What is non-deterministic finalization?
The hugely simplistic version is that every time it
garbage-collects, it starts by assuming everything to be garbage, then goes
through and builds a list of everything reachable. Those become not-garbage,
everything else doesn't, and gets thrown away. What makes it generational is
that every time an object goes through this process and survives, it is noted
as being a member of an older generation (up to 2, right now). When the
garbage-collector is trying to free memory, it starts with the lowest
generation (0) and only works up to higher ones if it can't free up enough
space, on the grounds that shorter-lived objects are more likely to have been
freed than longer-lived ones.
Non-deterministic finalization implies that the
destructor (if any) of an object will not necessarily be run (nor its memory
cleaned up, but that's a relatively minor issue) immediately upon its going out
of scope. Instead, it will wait until first the garbage collector gets around
to finding it, and then the finalisation queue empties down to it; and if the
process ends before this happens, it may not be finalised at all. (Although the
operating system will usually clean up any process-external resources left open
- note the usually there, especially as the exceptions tend to hurt a lot.)
What is the difference between Finalize() and
Dispose()?
Dispose() is called by the user of an object to
indicate that he is finished with it, enabling that object to release any
unmanaged resources it holds. Finalize() is called by the run-time to allow an
object which has not had Dispose() called on it to do the same. However,
Dispose() operates determinalistically, whereas there is no guarantee that
Finalize() will be called immediately when an object goes out of scope - or
indeed at all, if the program ends before that object is GCed - and as such
Dispose() is generally preferred.
How is the using() pattern useful? What is
IDisposable? How does it support deterministic finalization?
The using() pattern is useful because it ensures
that Dispose() will always be called when a disposable object (defined as one
that implements IDisposable, and thus the Dispose() method) goes out of scope,
even if it does so by an exception being thrown, and thus that resources are
always released.
What does this useful command line do? tasklist /m
"mscor*"
Lists all the applications and associated tasks/process currently running
on the system with a module whose name begins "mscor" loaded into
them; which in nearly all cases means "all the .NET processes".
What’s wrong with a line like this?
DateTime.Parse(myString);
Therez nothing wrong with this declaration.Converts
the specified string representation of a date and time to its DateTime
equivalent.But If the string is not a valid DateTime,It throws an exception.
What are PDBs? Where must they be located for
debugging to work?
A program database (PDB) files holds debugging and project state information
that allows incremental linking of debug configuration of your program.There
are several different types of symbolic debugging information. The default type
for Microsoft compiler is the so-called PDB file. The compiler setting for
creating this file is /Zi, or /ZI for C/C++(which creates a PDB file with
additional information that enables a feature called ""Edit and
Continue"") or a Visual Basic/C#/JScript .NET program with /debug.
A PDB file is a separate file, placed by default in
the Debug project subdirectory, that has the same name as the executable file
with the extension .pdb. Note that the Visual C++ compiler by default creates
an additional PDB file called VC60.pdb for VisulaC++6.0 and VC70.PDB file for
VisulaC++7.0. The compiler creates this file during compilation of the source
code, when the compiler isn't aware of the final name of the executable. The
linker can merge this temporary PDB file into the main one if you tell it to,
but it won't do it by default. The PDB file can be useful to display the
detailed stack trace with source files and line numbers.
What is FullTrust? Do GAC’ed assemblies have
FullTrust?
Before the .NET Framework existed, Windows had two
levels of trust for downloaded code. This old model was a binary trust model.
You only had two choices: Full Trust, and No Trust. The code could either do
anything you could do, or it wouldn't run at all.
The permission sets in .NET include FullTrust, SkipVerification, Execution,
Nothing, LocalIntranet, Internet and Everything. Full Trust Grants unrestricted
permissions to system resources. Fully trusted code run by a normal,
nonprivileged user cannot do administrative tasks, but can access any resources
the user can access, and do anything the user can do. From a security
standpoint, you can think of fully trusted code as being similar to native, unmanaged
code, like a traditional ActiveX control.
GAC assemblies are granted FullTrust. In v1.0 and 1.1, the fact that assemblies
in the GAC seem to always get a FullTrust grant is actually a side effect of
the fact that the GAC lives on the local machine. If anyone were to lock
down the security policy by changing the grant set of the local machine to
something less than FullTrust, and if your assembly did not get extra
permission from some other code group, it would no longer have FullTrust even
though it lives in the GAC.
What does this do? gacutil /l | find /i
"Corillian"
The Global Assembly Cache tool allows you to view and manipulate the contents
of the global assembly cache and download cache.The tool comes with various
optional params to do that.
""/l"" option Lists the contents of the global assembly
cache. If you specify the assemblyName parameter(/l [assemblyName]), the tool
lists only the assemblies matching that name.
What does this do .. sn -t foo.dll ?
Sn -t option displays the token for the public key
stored in infile. The contents of infile must be previously generated using -p.
Sn.exe computes the token using a hash function from the public key. To save
space, the common language runtime stores public key tokens in the manifest as
part of a reference to another assembly when it records a dependency to an
assembly that has a strong name. The -tp option displays the public key in
addition to the token.
How do you generate a strong name?
.NET provides an utility called strong name tool. You can run this toolfrom the
VS.NET command prompt to generate a strong name with an option "-k"
and providing the strong key file name. i.e. sn- -k < file-name >
What is the difference between a Debug and Release
build? Is there a significant speed difference? Why or why not?
The Debug build is the program compiled with full symbolic debug information
and no optimization. The Release build is the program compiled employing
optimization and contains no symbolic debug information. These settings can be
changed as per need from Project Configuration properties. The release runs
faster since it does not have any debug symbols and is optimized.
Explain the use of virtual, sealed, override, and
abstract.
Abstract: The keyword can be applied for a class or
method.
1. Class: If we use abstract keyword for a class it makes the
class an abstract class, which means it cant be instantiated. Though
it is not nessacary to make all the method within the abstract class to
be virtual. ie, Abstract class can have concrete methods
2. Method: If we make a method as abstract, we dont need to provide
implementation
of the method in the class but the derived class need to implement/override
this method.
Sealed: It can be applied on a class and methods. It stops the type from further
derivation i.e no one can derive class
from a sealed class,ie A sealed class cannot be inherited.A sealed class cannot
be a abstract class.A compile time error is thrown if you try to specify sealed
class as a base class.
When an instance method declaration includes a sealed modifier, that method is
said to be a sealed method. If an instance method declaration includes the
sealed modifier, it must also include the override modifier. Use of the sealed
modifier prevents a derived class from further overriding the method For
Egs: sealed override public void Sample() { Console.WriteLine("Sealed
Method"); }
Virtual & Override: Virtual & Override keywords provides runtime
polymorphism. A base class can make some of its methods
as virtual which allows the derived class a chance to override the base class
implementation by using override keyword.
For e.g. class Shape
{
int a
public virtual void Display()
{
Console.WriteLine("Shape");
}
}
class Rectangle:Shape
{
public override void Display()
{
Console.WriteLine("Derived");
}
}
Explain the importance and use of each, Version, Culture and
PublicKeyToken for an assembly.
This three alongwith name of the assembly provide a strong name or fully
qualified name to the assembly. When a assebly is referenced with all three.
PublicKeyToken: Each assembly can have a public key
embedded in its manifest that identifies the developer. This ensures that once
the assembly ships, no one can modify the code or other resources contained in
the assembly.
Culture: Specifies which culture the assembly supports
Version: The version number of the assembly.It is of the following form
major.minor.build.revision.
Explain the differences between public, protected,
private and internal.
These all are access modifier and they governs the access level. They can be
applied to class, methods, fields.
Public: Allows class, methods, fields to be accessible from anywhere i.e.
within and outside an assembly.
Private: When applied to field and method allows to be accessible within a
class.
Protected: Similar to private but can be accessed by members of derived class
also.
Internal: They are public within the assembly i.e. they can be accessed by
anyone within an assembly but outside assembly they are not visible.
What is the difference between typeof(foo) and
myFoo.GetType()?
Typeof is operator which applied to a object returns System.Type object. Typeof
cannot be overloaded white GetType has lot of overloads.GetType is a method
which also returns System.Type of an object. GetType is used to get the runtime
type of the object.
Example from MSDN showing Gettype used to retrive
type at untime:-
public class MyBaseClass: Object {
}
public class MyDerivedClass: MyBaseClass {
}
public class Test {
public static void Main() {
MyBaseClass myBase = new MyBaseClass();
MyDerivedClass myDerived = new MyDerivedClass();
object o = myDerived;
MyBaseClass b = myDerived;
Console.WriteLine("mybase: Type is {0}", myBase.GetType());
Console.WriteLine("myDerived: Type is
{0}", myDerived.GetType());
Console.WriteLine("object o = myDerived:
Type is {0}", o.GetType());
Console.WriteLine("MyBaseClass b =
myDerived: Type is {0}", b.GetType());
}
}
/*
This code produces the following output.
mybase: Type is MyBaseClass
myDerived: Type is MyDerivedClass
object o = myDerived: Type is MyDerivedClass
MyBaseClass b = myDerived: Type is MyDerivedClass
*/
Can "this" be used within a static method?
No 'This' cannot be used in a static method. As only
static variables/methods can be used in a static method.
What is the purpose of XML Namespaces?
An XML Namespace is a collection of element types and attribute names. It
consists of 2 parts
1) The first part is the URI used to identify the namespace
2) The second part is the element type or attribute name itself.
Together they form a unique name. The various purpose of XML Namespace are
1. Combine fragments from different documents
without any naming conflicts. (See example below.)
2. Write reusable code modules that can be invoked for specific elements and
attributes. Universally unique names guarantee that
such modules are invoked only for the correct elements and attributes.
3. Define elements and attributes that can be reused in other schemas or
instance documents without fear of name collisions. For
example, you might use XHTML elements in a parts catalog to provide part
descriptions. Or you might use the nil attribute
defined in XML Schemas to indicate a missing value.
< Department >
< Name >DVS1< /Name >
< addr:Address xmlns:addr="http://www.tu-darmstadt.de/ito/addresses"
>
< addr:Street >Wilhelminenstr.
7< /addr:Street >
< addr:City >Darmstadt< /addr:City
>
< addr:State >Hessen<
/addr:State >
< addr:Country >Germany<
/addr:Country >
< addr:PostalCode >D-64285<
/addr:PostalCode >
< /addr:Address >
< serv:Server xmlns:serv="http://www.tu-darmstadt.de/ito/servers"
>
< serv:Name >OurWebServer<
/serv:Name >
< serv:Address
>123.45.67.8< /serv:Address >
< /serv:Server >
< /Department >
What is difference between MetaData and Manifest ?
Metadata and Manifest forms an integral part of an
assembly( dll / exe ) in .net framework .
Out of which Metadata is a mandatory component , which as the name suggests
gives the details about various components of IL code viz : Methods ,
properties , fields , class etc.
Essentially Metadata maintains details in form of
tables like Methods Metadata tables , Properties Metadata tables , which
maintains the list of given type and other details like access specifier ,
return type etc.
Now Manifest is a part of metadata only , fully
called as “manifest metadata tables” , it contains the details of the
references needed by the assembly of any other external assembly / type , it
could be a custom assembly or standard System namespace .
Now for an assembly that can independently exists
and used in the .Net world both the things ( Metadata with Manifest ) are
mandatory , so that it can be fully described assembly and can be ported
anywhere without any system dependency . Essentially .Net framework can read
all assembly related information from assembly itself at runtime .
But for .Net modules , that can’t be used
independently , until they are being packaged as a part of an assembly , they
don’t contain Manifest but their complete structure is defined by their respective
metadata .
Ultimately . .Net modules use Manifest Metadata
tables of parent assembly which contain them .
What is the use of Internal keyword?
Internal keyword is one of the access specifier available in .Net framework ,
that makes a type visible in a given assembly , for e.g : a single dll
can contain multiple modules , essentially a multi file assembly , but it forms
a single binary component , so any type with internal keyword will be visible
throughout the assembly and can be used in any of the modules .
What actually happes when you add a something to arraylistcollection ?
Following things will happen :
Arraylist is a dynamic array class in c# in
System.Collections namespace derived from interfaces – ICollection , IList ,
ICloneable , IConvertible . It terms of in memory structure following is
the implementation .
a. Check up the total space if there’s any free
space on the declared list .
b. If yes add the new item and increase count by 1 .
c. If No Copy the whole thing to a temporary Array of Last Max. Size .
d. Create new Array with size ( Last Array Size + Increase Value )
e. Copy back values from temp and reference this new array as original array .
f. Must doing Method updates too , need to check it up .
What is Boxing and unboxing? Does it occure
automaatically or u need to write code to box and unbox?
Boxing – Process of converting a System.ValueType to
Reference Type , Mostly base class System.Object type and allocating it memory
on Heap .Reverse is unboxing , but can only be done with prior boxed variables.
Boxing is always implicit but Unboxing needs to be
explicitly done via casting , thus ensuring the value type contained inside .
How Boxing and unboxing occures in memory?
Boxing converts value type to reference type , thus allocating memory on Heap .
Unboxing converts already boxed reference types to value types through explicit
casting , thus allocating memory on stack .
Why only boxed types can be unboxed?
Unboxing is the process of converting a Reference type variable to Value
type and thus allocating memory on the stack . It happens only to those
Reference type variables that have been earlier created by Boxing of a Value
Type , therefore internally they contain a value type , which can be obtained
through explicit casting . For any other Reference type , they don’t internally
contain a Value type to Unboxed via explicit casting . This is why only boxed
types can be unboxed .
ASP.NET FAQ's
What is view state and use of it?
The current property settings of an ASP.NET page and
those of any ASP.NET server controls contained within the page. ASP.NET can
detect when a form is requested for the first time versus when the form is
posted (sent to the server), which allows you to program accordingly.
What are user controls and custom controls?
Custom controls:
A control authored by a user or a third-party software vendor that does
not belong to the .NET Framework class library. This is a generic term
that includes user controls. A custom server control is used in Web Forms
(ASP.NET pages). A custom client control is used in Windows Forms
applications.
User Controls:
In ASP.NET: A user-authored server control that enables an ASP.NET page to
be re-used as a server control. An ASP.NET user control is authored
declaratively and persisted as a text file with an .ascx extension.
The ASP.NET page framework compiles a user control on the fly to a class
that derives from the
System.Web.UI.UserControl class.
What are the validation controls?
A set of server controls included with ASP.NET that test user input in
HTML and Web server controls for programmer-defined requirements.
Validation controls perform input checking in server code. If the user is
working with a browser that supports DHTML, the validation controls can
also perform validation using client script.
What's the difference between
Response.Write() andResponse.Output.Write()?
The latter one allows you to write formattedoutput.
What methods are fired during the page load?
Init()
When the page is instantiated, Load() - when the page is
loaded into server memory,PreRender () - the brief moment before the
page is displayed to the user as HTML, Unload() - when page
finishes loading.
Where does the Web page belong in the .NET
Framework class hierarchy?
System.Web.UI.Page
Where do you store the information about the
user's locale?
System.Web.UI.Page.Culture
What's the difference between
Codebehind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"?
CodeBehind is relevant to Visual Studio.NET only.
What's a bubbled event?
When you have a complex control, likeDataGrid, writing an event processing
routine for each object (cell, button,row, etc.) is quite tedious. The
controls can bubble up their eventhandlers, allowing the main DataGrid
event handler to take care of its constituents.
Suppose you want a certain ASP.NET function executed on MouseOver over a
certain button.
Where do you add an event handler?
It's the Attributesproperty, the Add function inside that
property.
e.g. btnSubmit.Attributes.Add("onMouseOver","someClientCode();")
What data type does the RangeValidator
control support?
Integer,String and Date.
What are the different types of caching?
Caching is a technique widely used in computing to increase performance by
keeping frequently accessed or expensive data in memory. In context of web
application, caching is used to retain the pages or data across HTTP
requests and reuse them without the expense of recreating them.ASP.NET has
3 kinds of caching strategiesOutput CachingFragment CachingData
CachingOutput Caching: Caches
the dynamic output generated by a request. Some times it is useful to
cache the output of a website even for a minute, which will result in a
better performance. For caching the whole page the page should have
OutputCache directive.<%@ OutputCache Duration="60"
VaryByParam="state" %>
Fragment Caching:
Caches the portion of the page generated by the request. Some times it is
not practical to cache the entire page, in such cases we can cache a
portion of page<%@ OutputCache Duration="120"
VaryByParam="CategoryID;SelectedID"%>
Data Caching:
Caches the objects programmatically. For data caching
asp.net provides a cache object for eg: cache["States"] = dsStates;
What do you mean by authentication and
authorization?
Authentication is the process of validating a user on the
credentials (username and password) and authorization
performs after authentication. After Authentication a user will
be verified for performing the various tasks, It access is
limited it is known as authorization.
What are different types of directives in
.NET?
@Page: Defines page-specific attributes used by the
ASP.NET page parser and compiler. Can be
included only in .aspx files <%@ Page AspCompat="TRUE"
language="C#" %>
@Control:Defines control-specific attributes used by the
ASP.NET page parser and compiler. Can be
included only in .ascx files. <%@ Control Language="VB"
EnableViewState="false" %>
@Import: Explicitly imports a namespace into a page or user
control. The Import directive cannot
have more than one namespace attribute. To import multiple
namespaces, use multiple @Import directives. <% @ Import
Namespace="System.web" %>
@Implements: Indicates that the current page or user control
implements the specified .NET framework
interface.<%@ Implements
Interface="System.Web.UI.IPostBackEventHandler" %>
@Register: Associates aliases with namespaces and class names
for concise notation in custom server control syntax.<%@ Register
Tagprefix="Acme" Tagname="AdRotator" Src="AdRotator.ascx"
%>
@Assembly: Links an assembly to the current page during
compilation, making all the
assembly's classes and interfaces available for use on the
page. <%@ Assembly Name="MyAssembly"
%><%@ Assembly Src="MySource.vb" %>
@OutputCache: Declaratively controls the output caching
policies of an ASP.NET page or a user
control contained in a page<%@ OutputCache Duration="#ofseconds"
Location="Any | Client | Downstream | Server | None"
Shared="True | False" VaryByControl="controlname"
VaryByCustom="browser | customstring"
VaryByHeader="headers" VaryByParam="parametername" %>
@Reference: Declaratively indicates that another user control
or page source file
should be dynamically compiled and
linked against the page in which this directive is declared.
How do I debug an ASP.NET application
that wasn't written with Visual Studio.NET and that doesn't use code-behind?
Start the DbgClr debugger that comes with the .NET
Framework SDK, open the file containing the code you
want to debug, and set your breakpoints. Start the ASP.NET application.
Go back to DbgClr, choose Debug Processes from the Tools menu, and
select aspnet_wp.exe from the list of processes. (If
aspnet_wp.exe doesn't appear in the list,check the "Show system
processes" box.) Click the Attach button to
attach to aspnet_wp.exe and begin debugging.
Be sure to enable debugging in the ASPX file before debugging it with DbgClr.
You can enable tell ASP.NET to build debug executables by placing a
<%@ Page Debug="true" %> statement at the top of an
ASPX file or a <COMPILATION debug="true"
/>statement in a Web.config file.
Can a user browsing my Web site read my
Web.config or Global.asax files?
No. The <HTTPHANDLERS>section of Machine.config, which holds the
master configuration settings for ASP.NET, contains entries that map ASAX
files, CONFIG files, and selected other file types to an HTTP handler
named HttpForbiddenHandler, which fails attempts to retrieve the
associated file. You can modify it by editing Machine.config or
including an section in a local Web.config file.
What's the difference between
Page.RegisterClientScriptBlock and Page.RegisterStartupScript?
RegisterClientScriptBlock is for returning blocks of client-side
script containing functions. RegisterStartupScript is for returning blocks
of client-script not packaged in functions-in other words, code that's
to execute when the page is loaded. The latter positions script blocks
near the end of the document so elements on the page that the script
interacts are loaded before the script runs.<%@ Reference
Control="MyControl.ascx" %>
Is it necessary to lock application state before
accessing it?
Only if you're performing a multistep update and
want the update to be treated as an atomic operation.
Here's an example:
Application.Lock ();
Application["ItemsSold"] = (int) Application["ItemsSold"] +
1;
Application["ItemsLeft"] = (int) Application["ItemsLeft"] -
1;
Application.UnLock ();
By locking application state before updating it and unlocking it afterwards,
you ensure that another request being processed on another thread doesn't
read application state at exactly the wrong time and see an
inconsistent view of it. If I update session state, should I lock it, too? Are
concurrent accesses by multiple requests executing on multiple threads a
concern with session state?
Concurrent accesses aren't an issue with session state, for two reasons. One,
it's unlikely that two requests from the same user will overlap. Two, if they
do overlap, ASP.NET locks down session state during request processing so that
two threads can't touch it at once. Session state is locked down when the
HttpApplication instance that's processing the request fires an
AcquireRequestState event and unlocked when it fires a ReleaseRequestState
event.
Do ASP.NET forms authentication cookies provide any
protection against replay attacks? Do they, for example, include the client's
IP address or anything else that would distinguish the real client from
an attacker?
No. If an authentication cookie is stolen, it can be used by an attacker. It's
up to you to prevent this from happening by using an
encrypted communications channel (HTTPS). Authentication cookies issued as
session cookies, do, however,include a time-out valid
that limits their lifetime. So a stolen session cookie
can only be used in replay attacks as long as the ticket inside the cookie is
valid. The default time-out interval is 30 minutes.You can change that by
modifying the timeout attribute accompanying the <forms> element in
Machine.config or a local Web.config file. Persistent authentication cookies do
not time-out and therefore are a more serious security threat if stolen.
How do I send e-mail from an ASP.NET application?
MailMessage message = new
MailMessage ();
message.From = <email>;
message.To = <email>;
message.Subject = "Scheduled
Power Outage";
message.Body = "Our servers
will be down tonight.";
SmtpMail.SmtpServer =
"localhost";
SmtpMail.Send (message);
MailMessage and SmtpMail are classes defined
in the .NET Framework Class Library's System.Web.Mail namespace. Due to a
security change made to ASP.NET just before it shipped, you need to set
SmtpMail's SmtpServer property to "localhost" even though
"localhost" is the default. In addition, you must use the IIS
configuration applet to enable localhost (127.0.0.1) to relay messages through
the local SMTP service.
What are VSDISCO files?
VSDISCO files are DISCO files that support dynamic
discovery of Web services. If you place the following VSDISCO file in a
directory on your Web server, for example, it returns references to
all ASMX and DISCO files in the host directory and any subdirectories
not noted in <exclude>
elements:
<?xml version="1.0" ?>
<dynamicDiscovery
xmlns="urn:schemas-dynamicdiscovery:disco.2000-03-17">
<exclude path="_vti_cnf" />
<exclude path="_vti_pvt" />
<exclude path="_vti_log" />
<exclude path="_vti_script" />
<exclude path="_vti_txt" />
</dynamicDiscovery>
How does dynamic discovery work?
ASP.NET maps the file name extension VSDISCO to an HTTP handler that scans the
host directory and subdirectories for ASMX and DISCO files and returns a
dynamically generated DISCO document. A client who requests a VSDISCO file gets
back what appears to be a static DISCO document.
Note that VSDISCO files are disabled in the release version of ASP.NET. You can
reenable them by uncommenting the line in the <httpHandlers>
section of Machine.config that maps *.vsdisco to
System.Web.Services.Discovery.DiscoveryRequestHandler and granting the
ASPNET user account permission to read the IIS metabase. However,
Microsoft is actively discouraging the use of VSDISCO files because they could
represent a threat to Web server security.
Is it possible to prevent a browser from caching an ASPX page?
Just call SetNoStore on the HttpCachePolicy object exposed through the
Response object's Cache property, as demonstrated here:
<%@ Page Language="C#"
%>
<html>
<body>
<%
Response.Cache.SetNoStore
();
Response.Write (DateTime.Now.ToLongTimeString ());
%>
</body>
</html>
SetNoStore works by returning a Cache-Control:
private, no-store header in the HTTP response. In this example, it prevents
caching of a Web page that shows the current time.
What does AspCompat="true" mean and when
should I use it?
AspCompat is an aid in migrating ASP pages to ASPX pages. It defaults to false
but should be set to true in any ASPX file that creates apartment-threaded COM
objects--that is, COM objects registered ThreadingModel=Apartment. That
includes all COM objects written with Visual Basic 6.0. AspCompat should
also be set to true (regardless of threading model) if the page creates
COM objects that access intrinsic ASP objects such as Request and Response. The
following directive sets AspCompat to true:
<%@ Page AspCompat="true" %>
Setting AspCompat to true does two things. First, it
makes intrinsic ASP objects available to the COM
components by placing unmanaged wrappers around the equivalent ASP.NET objects.
Second, it improves the performance of calls that the page places to apartment-
threaded COM objects by ensuring that the page (actually, the thread that
processes the request for the page) and the COM objects it creates share
an apartment. AspCompat="true" forces ASP.NET request threads into
single-threaded apartments (STAs). If those threads create COM objects marked
ThreadingModel=Apartment, then the objects are created in the same STAs as the
threads that created them. Without AspCompat="true," request threads
run in a multithreaded apartment (MTA) and each call to an STA-based COM object
incurs a performance hit when it's marshaled across apartment boundaries.
Do not set AspCompat to true if your page uses no
COM objects or if it uses COM objects that don't access ASP intrinsic objects
and that are registered ThreadingModel=Free or ThreadingModel=Both.
Explain the differences between Server-side and
Client-side code?
Server side scripting means that all the
script will be executed by the server and interpreted as needed. ASP
doesn't have some of the functionality like sockets, uploading, etc. For
these you have to make a custom components usually in VB or VC++. Client
side scripting means that the script will be executed immediately in the
browser such as form field validation, clock, email validation, etc. Client
side scripting is usually done in VBScript or JavaScript. Download time,
browser compatibility, and visible code - since JavaScript and VBScript
code is included in the HTML page, then anyone can see the code by viewing the
page source. Also a possible security hazards for the client computer.
What type of code (server or client) is found in a
Code-Behind class?
C#
Should validation (did the user enter a real date)
occur server-side or client-side? Why?
Client-side validation because there is no need to
request a server side date when you could obtain a date from the client
machine.
What are ASP.NET Web Forms? How is this technology
different than what is available though ASP?
Web Forms are the heart and soul of ASP.NET. Web
Forms are the User Interface (UI) elements that give your Web applications
their look and feel. Web Forms are similar to Windows Forms in that they
provide properties, methods, and events for the controls that are placed
onto them. However, these UI elements render themselves in the
appropriate markup language required by the request, e.g. HTML. If
you use Microsoft Visual Studio .NET, you will also get the familiar
drag-and-drop interface used to create your UI for your Web application.
What is the difference between Server.Transfer and
Response.Redirect? Why would I choose one over the other?
In earlier versions of IIS, if we wanted to send a user to a new Web page, the
only option we had was Response.Redirect. While this method does accomplish our
goal, it has several important drawbacks. The biggest problem is that this
method causes each page to be treated as a separate transaction. Besides making
it difficult to maintain your transactional integrity,
Response.Redirect introduces some additional headaches. First, it prevents good
encapsulation of code. Second, you lose access to all of the properties in the
Request object. Sure, there are workarounds, but they're difficult.
Finally, Response.Redirect necessitates a round trip to the client,
which, on high-volume sites, causes scalability problems.
As you might suspect, Server.Transfer fixes all of these problems. It does this
by performing the transfer on the server without requiring a roundtrip to the
client.
How can you provide an alternating color scheme in a
Repeater control?
AlternatingItemTemplate Like the ItemTemplate
element, but rendered for every other row (alternating items) in the Repeater
control. You can specify a different appearance for the AlternatingItemTemplate
element by setting its style properties.
Which template must you provide, in order to display
data in a Repeater control?
ItemTemplate
What event handlers can I include in Global.asax?
Application_Start,Application_End,
Application_AcquireRequestState, Application_AuthenticateRequest,
Application_AuthorizeRequest, Application_BeginRequest,
Application_Disposed, Application_EndRequest, Application_Error, Application_PostRequestHandlerExecute,
Application_PreRequestHandlerExecute,
Application_PreSendRequestContent, Application_PreSendRequestHeaders,
Application_ReleaseRequestState, Application_ResolveRequestCache,
Application_UpdateRequestCache, Session_Start,Session_End
You can optionally include "On" in any of method names. For example,
you can name a BeginRequest event handler.Application_BeginRequest or
Application_OnBeginRequest.You can also include event handlers in Global.asax
for events fired by custom HTTP modules.Note that not all of the event handlers
make sense for Web Services (they're designed for ASP.NET applications in
general, whereas .NET XML Web Services are specialized instances of an ASP.NET
app). For example, the Application_AuthenticateRequest and
Application_AuthorizeRequest events are designed to be used with ASP.NET Forms
authentication.
What is different b/w webconfig.xml &
Machineconfig.xml
Web.config & machine.config both are
configuration files.Web.config contains settings specific to an application
where as machine.config contains settings to a computer. The Configuration
system first searches settings in machine.config file & then looks in
application configuration files.Web.config, can appear in multiple
directories on an ASP.NET Web application server. Each Web.config file applies
configuration settings to its own directory and all child directories below it.
There is only Machine.config file on a web server.
If I'm developing an application that must
accomodate multiple security levels though secure login and my ASP.NET web
appplication is spanned across three web-servers (using round-robbin load
balancing) what would be the best approach to maintain login-in state for the
users?
Use the state server or store the state in the database. This can be easily
done through simple setting change in the web.config.
<SESSIONSTATE
StateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data source=127.0.0.1; user id=sa; password="
cookieless="false"
timeout="30"
/>
You can specify mode as “stateserver” or
“sqlserver”.
Where would you use an iHTTPModule, and what are the
limitations of any approach you might take in implementing one
"One of ASP.NET's most useful features is the extensibility of the HTTP
pipeline, the path that data takes between client and server. You can use them
to extend your ASP.NET applications by adding pre- and post-processing to each
HTTP request coming into your application. For example, if you wanted custom
authentication facilities for your application, the best technique would be to
intercept the request when it comes in and process the request in a custom HTTP
module.
How do you turn off cookies for one page in your
site?
Since no Page Level directive is present, I am afraid that cant be done.
How do you create a permanent cookie?
Permanent cookies are available until a specified
expiration date, and are stored on the hard disk.So Set the 'Expires' property
any value greater than DataTime.MinValue with respect to the current datetime.
If u want the cookie which never expires set its Expires property equal to
DateTime.maxValue.
Which method do you use to redirect the user to
another page without performing a round trip to the client?
Server.Transfer and Server.Execute
What property do you have to set to tell the grid
which page to go to when using the Pager object?
CurrentPageIndex
Should validation (did the user enter a real date)
occur server-side or client-side? Why?
It should occur both at client-side and Server
side.By using expression validator control with the specified expression ie..
the regular expression provides the facility of only validatating the date
specified is in the correct format or not. But for checking the date where it
is the real data or not should be done at the server side, by getting the
system date ranges and checking the date whether it is in between that range or
not.
What does the "EnableViewState" property
do? Why would I want it on or off?
Enable ViewState turns on the automatic state management feature that enables
server controls to re-populate their values on a round trip without requiring
you to write any code. This feature is not free however, since the state of a
control is passed to and from the server in a hidden form field. You should be
aware of when ViewState is helping you and when it is not. For example, if you
are binding a control to data on every round trip, then you do not need the
control to maintain it's view state, since you will wipe out any re-populated
data in any case. ViewState is enabled for all server controls by default. To
disable it, set the EnableViewState property of the control to false.
What is the difference between Server.Transfer and
Response.Redirect? Why would I choose one over the other?
Server.Transfer() : client is shown as it is on the
requesting page only, but the all the content is of the requested page. Data
can be persist accros the pages using Context.Item collection, which is one of
the best way to transfer data from one page to another keeping the page state
alive.
Response.Dedirect() :client know the physical
location (page name and query string as well). Context.Items loses the
persisitance when nevigate to destination page. In earlier versions of IIS, if
we wanted to send a user to a new Web page, the only option we had was
Response.Redirect. While this method does accomplish our goal, it has several
important drawbacks. The biggest problem is that this method causes each page
to be treated as a separate transaction. Besides making it difficult to
maintain your transactional integrity, Response.Redirect introduces some
additional headaches. First, it prevents good encapsulation of code. Second,
you lose access to all of the properties in the Request object. Sure, there are
workarounds, but they're difficult. Finally, Response.Redirect necessitates a
round trip to the client, which, on high-volume sites, causes scalability
problems. As you might suspect, Server.Transfer fixes all of these problems. It
does this by performing the transfer on the server without requiring a
roundtrip to the client.
Can you give an example of when it would be appropriate to use a web
service as opposed to a non-serviced .NET component?
- Communicating
through a Firewall When building a distributed application with 100s/1000s
of users spread over multiple locations, there is always the problem of
communicating between client and server because of firewalls and proxy
servers. Exposing your middle tier components as Web Services and invoking
the directly from a Windows UI is a very valid option.
- Application
Integration When integrating applications written in various languages and
running on disparate systems. Or even applications running on the same
platform that have been written by separate vendors.
- Business-to-Business
Integration This is an enabler for B2B intergtation which allows one to
expose vital business processes to authorized supplier and customers. An
example would be exposing electronic ordering and invoicing, allowing
customers to send you purchase orders and suppliers to send you invoices
electronically.
- Software
Reuse This takes place at multiple levels. Code Reuse at the Source code
level or binary componet-based resuse. The limiting factor here is that
you can reuse the code but not the data behind it. Webservice overcome
this limitation. A scenario could be when you are building an app that
aggregates the functionality of serveral other Applicatons. Each of these
functions could be performed by individual apps, but there is value in
perhaps combining the the multiple apps to present a unifiend view in a
Portal or Intranet.
- When
not to use Web Services: Single machine Applicatons When the apps are
running on the same machine and need to communicate with each other use a
native API. You also have the options of using component technologies such
as COM or .NET Componets as there is very little overhead.
- Homogeneous
Applications on a LAN If you have Win32 or Winforms apps that want to
communicate to their server counterpart. It is much more efficient to use
DCOM in the case of Win32 apps and .NET Remoting in the case of .NET Apps
Can you give an example of what might be best suited
to place in the Application_Start and Session_Start subroutines?
The Application_Start event is guaranteed to occur
only once throughout the lifetime of the application. It's a good place to
initialize global variables. For example, you might want to retrieve a list of
products from a database table and place the list in application state or the
Cache object. SessionStateModule exposes both Session_Start and Session_End
events.
What are the advantages and disadvantages of
viewstate?
The primary advantages of the ViewState feature in
ASP.NET are:
1. Simplicity. There is no need to write possibly
complex code to store form data between page submissions.
2. Flexibility. It is possible to enable, configure, and disable ViewState on a
control-by-control basis, choosing to persist the values of some fields but not
others.
There are, however a few disadvantages that are
worth pointing out:
1. Does not track across pages. ViewState
information does not automatically transfer from page to page. With the session
approach, values can be stored in the session and accessed from other pages.
This is not possible with ViewState, so storing
data into the session must be done explicitly.
2. ViewState is not suitable for transferring data
for back-end systems. That is, data still has to be transferred to the back
end using some form of data object.
Describe session handling in a webfarm, how does it
work and what are the limits?
ASP.NET Session supports storing of session data in
3 ways, i] in In-Process ( in the same memory that ASP.NET uses) , ii]
out-of-process using Windows NT Service )in separate memory from ASP.NET ) or
iii] in SQL Server (persistent storage). Both the Windows Service and SQL
Server solution support a webfarm scenario where all the web-servers can be
configured to share common session state store.
1. Windows Service :
We can start this service by Start | Control Panel | Administrative Tools |
Services | . In that we service names ASP.NET State Service. We can start
or stop service by manually or configure to start automatically. Then we have
to configure our web.config file
<CONFIGURATION><configuration>
<system.web>
<SessionState
mode = “StateServer”
stateConnectionString = “tcpip=127.0.0.1:42424”
stateNetworkTimeout = “10”
sqlConnectionString=”data source = 127.0.0.1; uid=sa;pwd=”
cookieless =”Flase”
timeout= “20” />
</system.web>
</configuration> </SYSTEM.WEB>
</CONFIGURATION>
Here ASP.Net Session is directed to use Windows Service for state management on
local server (address : 127.0.0.1 is TCP/IP loop-back address). The default
port is 42424. we can configure to any port but for that we have to manually
edit the registry.
Follow these simple steps
- In a webfarm make sure you have the same config file in all your web servers.
- Also make sure your objects are serializable.
- For session state to be maintained across different web servers in the
webfarm, the application path of the web-site in the IIS Metabase should be
identical in all the web-servers in the webfarm.
Which template must you provide, in order to display
data in a Repeater control?
You have to use the ItemTemplate to Display data.
Syntax is as follows,
< ItemTemplate >
< div class =”rItem” >
< img src=”images/<%#
Container.DataItem(“ImageURL”)%>” hspace=”10” />
< b > <% # Container.DataItem(“Title”)%>
< /div >
< ItemTemplate >
How can you provide an alternating color scheme in a
Repeater control?
Using the AlternatintItemTemplate
What property must you set, and what method must you
call in your code, in order to bind the data from some data source to the
Repeater control?
Set the DataMember property to the name of the table
to bind to. (If this property is not set, by default the first table in the
dataset is used.)
DataBind method, use this method to bind data from a source to a server
control. This method is commonly used after retrieving a data set through a
database query.
What method do you use to explicitly kill a user s
session?
You can dump (Kill) the session yourself by calling
the method Session.Abandon.
ASP.NET automatically deletes a user's Session
object, dumping its contents, after it has been idle for a configurable timeout
interval. This interval, in minutes, is set in the <SESSIONSTATE>section
of the web.config file. The default is 20 minutes.
How do you turn off cookies for one page in your
site?
Use Cookie.Discard property, Gets or sets the discard flag set by the server.
When true, this property instructs the client application not to save the
Cookie on the user's hard disk when a session ends.
Which two properties are on every validation
control?
We have two common properties for every validation
controls
1. Control to Validate,
2. Error Message.
What tags do you need to add within the asp:datagrid
tags to bind columns manually?
< asp:DataGrid
id="dgCart" AutoGenerateColumns="False"
CellPadding="4" Width="448px"
runat="server" >
< Columns >
< asp:ButtonColumn HeaderText="SELECT" Text="SELECT"
CommandName="select" >< /asp:ButtonColumn >
< asp:BoundColumn DataField="ProductId" HeaderText="Product
ID" >< /asp:BoundColumn >
< asp:BoundColumn DataField="ProductName" HeaderText="Product
Name" >< /asp:BoundColumn >
< asp:BoundColumn DataField="UnitPrice"
HeaderText="UnitPrice" >< /asp:BoundColumn >
< /Columns >
< /asp:DataGrid >
How do you create a permanent cookie?
Permanent cookies are the ones that are most useful. Permanent cookies are
available until a specified expiration date, and are stored on the hard disk.
The location of cookies differs with each browser, but this doesn’t matter, as
this is all handled by your browser and the server. If you want to create a
permanent cookie called Name with a value of Nigel, which expires in one month,
you’d use the following code
Response.Cookies ("Name") = "Nigel"
Response.Cookies ("Name"). Expires = DateAdd ("m", 1, Now
())
What tag do you use to add a hyperlink column to the
DataGrid?
< asp:HyperLinkColumn > </
asp:HyperLinkColumn>
Which method do you use to redirect the user to
another page without performing a round trip to the client?
Server.transfer
What is the transport protocol you use to call a Web
service SOAP ?
HTTP Protocol
Explain role based security ?
Role Based Security lets you identify groups of users to allow or deny based on
their role in the organization.In Windows NT and Windows XP, roles map to names
used to identify user groups. Windows defines several built-in groups,
including Administrators, Users, and Guests.To allow or deny access to certain
groups of users, add the <ROLES>element to the authorization list in your
Web application's Web.config file.e.g.
<AUTHORIZATION>< authorization >
< allow roles="Domain Name\Administrators" /
> < !-- Allow Administrators in domain. -- >
< deny users="*" /
>
< !-- Deny anyone else. -- >
< /authorization >
How do you register JavaScript for webcontrols ?
You can register javascript for controls using
<CONTROL -name>Attribtues.Add(scriptname,scripttext) method.
When do you set "<IDENTITY
impersonate="true" />" ?
Identity is a webconfig declaration under System.web, which helps to control
the application Identity of the web applicaton. Which can be at any
level(Machine,Site,application,subdirectory,or page), attribute impersonate
with "true" as value specifies that client impersonation is used.
What are different templates available in
Repeater,DataList and Datagrid ?
Templates enable one to apply complicated formatting
to each of the items displayed by a control.Repeater control supports five
types of templates.HeaderTemplate controls how the header of the repeater
control is formatted.ItemTemplate controls the formatting of each item
displayed.AlternatingItemTemplate controls how alternate items are formatted
and the SeparatorTemplate displays a separator between each item
displyed.FooterTemplate is used for controlling how the footer of the
repeater control is formatted.The DataList and Datagrid supports two templates
in addition to the above five.SelectedItem Template controls how a selected
item is formatted and EditItemTemplate controls how an item selected for
editing is formatted.
What is ViewState ? and how it is managed ?
ASP.NET ViewState is a new kind of state service
that developers can use to track UI state on a per-user basis. Internally
it uses an an old Web programming trick-roundtripping state in a hidden
form field and bakes it right into the page-processing framework.It needs less
code to write and maintain state in your Web-based forms.
What is web.config file ?
Web.config file is the configuration file for the
Asp.net web application. There is one web.config file for one asp.net
application which configures
the particular application. Web.config file is written in XML with
specific tags having specific meanings.It includes databa which includes
connections,Session States,Error Handling,Security etc.
For example :
< configuration >
< appSettings >
< add key="ConnectionString"
value="server=localhost;uid=sa;pwd=;database=MyDB"
/ >
< /appSettings >
< /configuration >
What is advantage of viewstate and what are benefits?
When a form is submitted in classic ASP, all form values are cleared.
Suppose you have submitted a form with a lot of information and the
server comes back with an error. You will have to go back to the form and
correct the information. You click the back button, and what happens.......ALL
form values are CLEARED, and you will have to start all over again! The site did
not maintain your ViewState.With ASP .NET, the form reappears in the
browser window together with all form values.This is because ASP .NET
maintains your ViewState. The ViewState indicates the status of the page
when submitted to the server.
What tags do you need to add within the asp:datagrid
tags to bind columns manually?
Set AutoGenerateColumns Property to false on the
datagrid tag and then use Column tag and an ASP:databound tag
< asp:DataGrid runat="server"
id="ManualColumnBinding" AutoGenerateColumns="False" >
< Columns >
< asp:BoundColumn
HeaderText="Column1" DataField="Column1"/ >
< asp:BoundColumn
HeaderText="Column2" DataField="Column2"/ >
< /Columns >
< /asp:DataGrid >
<asp:DataGrid id=ManualColumnBinding runat="server"
AutoGenerateColumns="False">
<COLUMNS> <asp:BoundColumn
HeaderText="Column2"
DataField="Column2"></asp:BoundColumn>
</asp:DataGrid>Which property on a Combo Box do you set with a
column name, prior to setting the DataSource, to display data in the combo box?
DataTextField and DataValueField
Which control would you use if you needed to make
sure the values in two different controls matched?
CompareValidator is used to ensure that two fields
are identical.
What is validationsummary server control?where it is
used?.
The ValidationSummary control allows you to summarize the error messages from
all validation controls on a Web page in a single location. The summary can be
displayed as a list, a bulleted list, or a single paragraph, based on the value
of the DisplayMode property. The error message displayed in the
ValidationSummary control for each validation control on the page is specified
by the ErrorMessage property of each validation control. If the ErrorMessage
property of the validation control is not set, no error message is displayed in
the ValidationSummary control for that validation control. You can also specify
a custom title in the heading section of the ValidationSummary control by
setting the HeaderText property.
You can control whether the ValidationSummary control is displayed or hidden by
setting the ShowSummary property. The summary can also be displayed in a
message box by setting the ShowMessageBox property to true.
What is the sequence of operation takes place when a
page is loaded?
BeginTranaction - only if the request is
transacted
Init - every time a page is processed
LoadViewState - Only on postback
ProcessPostData1 - Only on postback
Load - every time
ProcessData2 - Only on Postback
RaiseChangedEvent - Only on Postback
RaisePostBackEvent - Only on Postback
PreRender - everytime
BuildTraceTree - only if tracing is enabled
SaveViewState - every time
Render - Everytime
End Transaction - only if the request is transacted
Trace.EndRequest - only when tracing is enabled
UnloadRecursive - Every request
Difference between asp and asp.net?.
"ASP (Active Server Pages) and ASP.NET are both server side technologies
for building web sites and web applications, ASP.NET is Managed compiled code -
asp is interpreted. and ASP.net is fully Object oriented. ASP.NET has been
entirely re-architected to provide a highly productive programming experience
based on the .NET Framework, and a robust infrastructure for building reliable
and scalable web
applications."
Name the validation control available in asp.net?.
RequiredField,
RangeValidator,RegularExpression,Custom validator,compare Validator
What are the various ways of securing a web site
that could prevent from hacking etc .. ?
1) Authentication/Authorization
2) Encryption/Decryption
3) Maintaining web servers outside the corporate firewall. etc.,
What is the difference between in-proc and
out-of-proc?
An inproc is one which runs in the same process area as that of the client
giving tha advantage of speed but the disadvantage of stability becoz if it
crashes it takes the client application also with it.Outproc is one which works
outside the clients memory thus giving stability to the client, but we have to
compromise a bit on speed.
When you’re running a component within ASP.NET, what
process is it running within on Windows XP? Windows 2000? Windows 2003?
On Windows 2003 (IIS 6.0) running in native mode,
the component is running within the w3wp.exe process associated with the
application pool which has been configured for the web application containing
the component.
On Windows 2003 in IIS 5.0 emulation mode, 2000, or
XP, it's running within the IIS helper process whose name I do not remember, it
being quite a while since I last used IIS 5.0.
What does aspnet_regiis -i do ?
Aspnet_regiis.exe is The ASP.NET IIS Registration
tool allows an administrator or installation program to easily update the
script maps for an ASP.NET application to point to the ASP.NET ISAPI version
associated with the tool. The tool can also be used to display the status of
all installed versions of ASP. NET, register the ASP.NET version coupled with
the tool, create client-script directories, and perform other configuration
operations.
When multiple versions of the .NET Framework are executing side-by-side on a
single computer, the ASP.NET ISAPI version mapped to an ASP.NET application
determines which version of the common language runtime is used for the
application.
The tool can be launched with a set of optional parameters. Option
"i" Installs the version of ASP.NET associated with Aspnet_regiis.exe
and updates the script maps at the IIS metabase root and below. Note that only
applications that are currently mapped to an earlier version of ASP.NET are
affected
What is a PostBack?
The process in which a Web page sends data back to the same page on the server.
What is ViewState? How is it encoded? Is it
encrypted? Who uses ViewState?
ViewState is the mechanism ASP.NET uses to keep
track of server control state values that don't otherwise post back as part of
the HTTP form. ViewState Maintains the UI State of a Page
ViewState is base64-encoded.
It is not encrypted but it can be encrypted by setting
EnableViewStatMAC="true" & setting the machineKey validation type
to 3DES. If you want to NOT maintain the ViewState, include the directive
< %@ Page EnableViewState="false" % > at the top of an .aspx
page or add the attribute EnableViewState="false" to any control.
What is the < machinekey > element and what
two ASP.NET technologies is it used for?
Configures keys to use for encryption and decryption
of forms authentication cookie data and view state data, and for verification
of out-of-process session state identification.There fore 2 ASP.Net technique
in which it is used are Encryption/Decryption & Verification
What three Session State providers are available in
ASP.NET 1.1? What are the pros and cons of each?
ASP.NET provides three distinct ways to store
session data for your application: in-process session state, out-of-process
session state as a Windows service, and out-of-process session state in a SQL
Server database. Each has it advantages.
1.In-process session-state mode
Limitations:
* When using the in-process session-state mode, session-state data is
lost if aspnet_wp.exe or the application domain restarts.
* If you enable Web garden mode in the < processModel > element of
the application's Web.config file, do not use in-process session-state mode.
Otherwise, random data loss can occur.
Advantage:
* in-process session state is by far the fastest solution. If you are
storing only small amounts of volatile data in session state, it is recommended
that you use the in-process provider.
2. The State Server simply stores session state in
memory when in out-of-proc mode. In this mode the worker process talks directly
to the State Server
3. SQL mode, session states are stored in a SQL
Server database and the worker process talks directly to SQL. The ASP.NET
worker processes are then able to take advantage of this simple storage service
by serializing and saving (using .NET serialization services) all objects
within a client's Session collection at the end of each Web request
Both these out-of-process solutions are useful primarily if you scale
your application across multiple processors or multiple computers, or where
data cannot be lost if a server or process is restarted.
What is the difference between HTTP-Post and
HTTP-Get?
As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying
protocol. Both of these methods encode request parameters as name/value pairs
in the HTTP request.
The GET method creates a query string and appends it to the script's URL on the
server that handles the request.
The POST method creates a name/value pairs that are passed in the body of the
HTTP request message.
Name and describe some HTTP Status Codes and
what they express to the requesting client.
When users try to access content on a server that is
running Internet Information Services (IIS) through HTTP or File Transfer
Protocol (FTP), IIS returns a numeric code that indicates the status of the
request. This status code is recorded in the IIS log, and it may also be
displayed in the Web browser or FTP client. The status code can indicate
whether a particular request is successful or unsuccessful and can also reveal
the exact reason why a request is unsuccessful. There are 5 groups ranging from
1xx - 5xx of http status codes exists.
101 - Switching protocols.
200 - OK. The client request has succeeded
302 - Object moved.
400 - Bad request.
500.13 - Web server is too busy.
Explain < @OutputCache% > and the usage of
VaryByParam, VaryByHeader.
OutputCache is used to control the caching policies
of an ASP.NET page or user control. To cache a page @OutputCache directive
should be defined as follows < %@ OutputCache Duration="100"
VaryByParam="none" % >
VaryByParam: A semicolon-separated list of strings
used to vary the output cache. By default, these strings correspond to a query
string value sent with GET method attributes, or a parameter sent using the POST
method. When this attribute is set to multiple parameters, the output cache
contains a different version of the requested document for each specified
parameter. Possible values include none, *, and any valid query string or POST
parameter name.
VaryByHeader: A semicolon-separated list of HTTP
headers used to vary the output cache. When this attribute is set to multiple
headers, the output cache contains a different version of the requested
document for each specified header.
What is the difference between repeater over
datalist and datagrid?
The Repeater class is not derived from the
WebControl class, like the DataGrid and DataList. Therefore, the Repeater lacks
the stylistic properties common to both the DataGrid and DataList. What this
boils down to is that if you want to format the data displayed in the Repeater,
you must do so in the HTML markup.
The Repeater control provides the maximum amount of flexibility over the HTML
produced. Whereas the DataGrid wraps the DataSource contents in an HTML <
table >, and the DataList wraps the contents in either an HTML < table
> or < span > tags (depending on the DataList's RepeatLayout
property), the Repeater adds absolutely no HTML content other than what you
explicitly specify in the templates.
While using Repeater control, If we wanted to display the employee names in a
bold font we'd have to alter the "ItemTemplate" to include an HTML
bold tag, Whereas with the DataGrid or DataList, we could have made the text
appear in a bold font by setting the control's ItemStyle-Font-Bold property to
True.
The Repeater's lack of stylistic properties can drastically add to the
development time metric. For example, imagine that you decide to use the
Repeater to display data that needs to be bold, centered, and displayed in a
particular font-face with a particular background color. While all this can be
specified using a few HTML tags, these tags will quickly clutter the Repeater's
templates. Such clutter makes it much harder to change the look at a later
date. Along with its increased development time, the Repeater also lacks any
built-in functionality to assist in supporting paging, editing, or editing of
data. Due to this lack of feature-support, the Repeater scores poorly on the
usability scale.
However, The Repeater's performance is slightly
better than that of the DataList's, and is more noticeably better than that of
the DataGrid's. Following figure shows the number of requests per second the
Repeater could handle versus the DataGrid and DataList
Can we handle the error and redirect to some pages
using web.config?
Yes, we can do this, but to handle errors, we must
know the error codes; only then we can take the user to a proper error message
page, else it may confuse the user.
CustomErrors Configuration section in web.config file:
The default configuration is:
< customErrors mode="RemoteOnly"
defaultRedirect="Customerror.aspx" >
< error statusCode="404" redirect="Notfound.aspx"
/ >
< /customErrors >
If mode is set to Off, custom error messages will be disabled. Users will
receive detailed exception error messages.
If mode is set to On, custom error messages will be enabled.
If mode is set to RemoteOnly, then users will receive custom errors, but users
accessing the site locally will receive detailed error messages.
Add an < error > tag for each error you want to handle. The error tag
will redirect the user to the Notfound.aspx page when the site returns the 404
(Page not found) error.
[Example]
There is a page MainForm.aspx
Private Sub Page_Load(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles MyBase.Load
'Put user code to initialize the
page here
Dim str As System.Text.StringBuilder
str.Append("hi") ' Error Line as str is not instantiated
Response.Write(str.ToString)
End Sub
[Web.Config]
< customErrors mode="On"
defaultRedirect="Error.aspx"/ >
' a simple redirect will take the user to Error.aspx [user defined] error file.
< customErrors mode="RemoteOnly"
defaultRedirect="Customerror.aspx" >
< error statusCode="404" redirect="Notfound.aspx"
/ >
< /customErrors >
'This will take the user to NotFound.aspx defined in IIS.
How do you implement Paging in .Net?
The DataGrid provides the means to display a group
of records from the data source (for example, the first 10), and then navigate
to the "page" containing the next 10 records, and so on through the
data.
Using Ado.Net we can explicit control over the
number of records returned from the data source, as well as how much data is to
be cached locally in the DataSet.
1.Using DataAdapter.fill method give the value of 'Maxrecords' parameter
(Note: - Don't use it because query will return all records but fill the
dataset based on value of 'maxrecords' parameter).
2.For SQL server database, combines a WHERE clause and a ORDER BY clause with
TOP predicate.
3.If Data does not change often just cache records locally in DataSet and just
take some records from the DataSet to display.
What is the difference between Server.Transfer and
Response.Redirect?
Server.Transfer() : client is shown as it is on the
requesting page only, but the all the content is of the requested page. Data
can be persist across the pages using Context.Item collection, which is one of
the best way to transfer data from one page to another keeping the page state
alive.
Response.Dedirect() :client knows the physical
location (page name and query string as well). Context.Items loses the
persistence when navigate to destination page. In earlier versions of IIS, if
we wanted to send a user to a new Web page, the only option we had was Response.Redirect.
While this method does accomplish our goal, it has several important drawbacks.
The biggest problem is that this method causes each page to be treated as a
separate transaction. Besides making it difficult to maintain your
transactional integrity, Response.Redirect introduces some additional
headaches. First, it prevents good encapsulation of code. Second, you lose
access to all of the properties in the Request object. Sure, there are
workarounds, but they're difficult. Finally, Response.Redirect necessitates a
round trip to the client, which, on high-volume sites, causes scalability
problems. As you might suspect, Server.Transfer fixes all of these problems. It
does this by performing the transfer on the server without requiring a
roundtrip to the client.
Response.Redirect sends a response to the client browser instructing it to
request the second page. This requires a round-trip to the client, and the
client initiates the Request for the second page. Server.Transfer transfers the
process to the second page without making a round-trip to the client. It also
transfers the HttpContext to the second page, enabling the second page access
to all the values in the HttpContext of the first page.
Can you create an app domain?
Yes, We can create user app domain by calling on of
the following overload static methods of the System.AppDomain class
1. Public static AppDomain CreateDomain(String friendlyName)
2. Public static AppDomain CreateDomain(String friendlyName, Evidence
securityInfo)
3. Public static AppDomain CreateDomain(String friendlyName, Evidence
securityInfo, AppDomainSetup info)
4. Public static AppDomain CreateDomain(String friendlyName, Evidence
securityInfo, String appBasePath, String appRelativeSearchPath, bool
shadowCopyFiles)
What are the various security methods which IIS Provides apart from
.NET ?
The various security methods which IIS provides are
a) Authentication Modes
b) IP Address and Domain Name Restriction
c) DNS Lookups DNS Lookups
d) The Network ID and Subnet Mask
e) SSL
What is Web Gardening? How would using it affect a design?
The Web Garden Model
The Web garden model is configurable through the section of the machine.config
file. Notice that the section is the only configuration section that cannot be
placed in an application-specific web.config file. This means that the Web
garden mode applies to all applications running on the machine. However, by
using the node in the machine.config source, you can adapt machine-wide
settings on a per-application basis.
Two attributes in the section affect the Web garden
model. They are webGarden and cpuMask. The webGarden attribute takes a Boolean
value that indicates whether or not multiple worker processes (one per each
affinitized CPU) have to be used. The attribute is set to false by default. The
cpuMask attribute stores a DWORD value whose binary representation provides a
bit mask for the CPUs that are eligible to run the ASP.NET worker process. The
default value is -1 (0xFFFFFF), which means that all available CPUs can be
used. The contents of the cpuMask attribute is ignored when the webGarden
attribute is false. The cpuMask attribute also sets an upper bound to the
number of copies of aspnet_wp.exe that are running.
Web gardening enables multiple worker processes to
run at the same time. However, you should note that all processes will have
their own copy of application state, in-process session state, ASP.NET cache,
static data, and all that is needed to run applications. When the Web garden
mode is enabled, the ASP.NET ISAPI launches as many worker processes as there
are CPUs, each a full clone of the next (and each affinitized with the
corresponding CPU). To balance the workload, incoming requests are partitioned
among running processes in a round-robin manner. Worker processes get recycled
as in the single processor case. Note that ASP.NET inherits any CPU usage
restriction from the operating system and doesn't include any custom semantics
for doing this.
All in all, the Web garden model is not necessarily
a big win for all applications. The more stateful applications are, the more
they risk to pay in terms of real performance. Working data is stored in blocks
of shared memory so that any changes entered by a process are immediately
visible to others. However, for the time it takes to service a request, working
data is copied in the context of the process. Each worker process, therefore,
will handle its own copy of working data, and the more stateful the
application, the higher the cost in performance. In this context, careful and savvy
application benchmarking is an absolute must.
Changes made to the section of the configuration
file are effective only after IIS is restarted. In IIS 6, Web gardening
parameters are stored in the IIS metabase; the webGarden and cpuMask attributes
are ignored.
What is view state?.where it stored?.can we disable
it?
The web is state-less protocol, so the page gets instantiated, executed,
rendered and then disposed on every round trip to the server. The developers
code to add "statefulness" to the page by using Server-side storage
for the state or posting the page to itself. When require to persist and read
the data in control on webform, developer had to read the values and store them
in hidden variable (in the form), which were then used to restore the values.
With advent of .NET framework, ASP.NET came up with ViewState mechanism, which
tracks the data values of server controls on ASP.NET webform. In
effect,ViewState can be viewed as "hidden variable managed by ASP.NET
framework!". When ASP.NET page is executed, data values from all server
controls on page are collected and encoded as single string, which then
assigned to page's hidden atrribute "< input type=hidden
>", that is part of page sent to the client.
ViewState value is temporarily saved in the client's
browser.ViewState can be disabled for a single control, for an entire page
orfor an entire web application. The syntax is:
Disable ViewState for control (Datagrid in this
example)
< asp:datagrid EnableViewState="false" ... / >
Disable ViewState for a page, using Page directive
< %@ Page EnableViewState="False" ... % >
Disable ViewState for application through entry in
web.config
< Pages EnableViewState="false" ... / >
ADO.NET
Explain what a diffgram is and its usage ?
A DiffGram is an XML format that is used to identify current and original
versions of data elements. The DataSet uses the DiffGram format to load and
persist its contents, and to serialize its contents for transport across a
network connection. When a DataSet is written as a DiffGram, it populates the
DiffGram with all the necessary information to accurately recreate the
contents, though not the schema, of the DataSet, including column values from
both the Original and Current row versions, row error information, and row
order.
When sending and retrieving a DataSet from an XML
Web service, the DiffGram format is implicitly used. Additionally, when loading
the contents of a DataSet from XML using the ReadXml method, or when writing
the contents of a DataSet in XML using the WriteXml method, you can select that
the contents be read or written as a DiffGram.
The DiffGram format is divided into three sections:
the current data, the original (or "before") data, and an errors
section, as shown in the following example.
<?xml version="1.0"?>
<diffgr:diffgram
xmlns:msdata="urn:schemas-microsoft-com:xml-msdata"
xmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1"
xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<DataInstance>
</DataInstance>
<diffgr:before>
</diffgr:before>
<diffgr:errors>
</diffgr:errors>
</diffgr:diffgram>
The DiffGram format consists of the following blocks
of data:
<DataInstance>
The name of this element, DataInstance, is used for explanation purposes in
this documentation. A DataInstance element represents a DataSet or a row of a
DataTable. Instead of DataInstance, the element would contain the name of the
DataSet or DataTable. This block of the DiffGram format contains the current
data, whether it has been modified or not. An element, or row, that has been
modified is identified with the diffgr:hasChanges annotation.
<diffgr:before>
This block of the DiffGram format contains the original version of a row.
Elements in this block are matched to elements in the DataInstance block using
the diffgr:id annotation.
<diffgr:errors>
This block of the DiffGram format contains error information for a particular
row in the DataInstance block. Elements in this block are matched to elements
in the DataInstance block using the diffgr:id annotation.
Which method do you invoke on the DataAdapter
control to load your generated dataset with data?
You have to use the Fill method of the DataAdapter control and pass the dataset
object as an argument to load the generated data.
Can you edit data in the Repeater control?
NO.
Which are the different IsolationLevels ?
Following are the various IsolationLevels:
- Serialized
Data read by a current transaction cannot be changed by another transaction
until the current transaction finishes. No new data can be inserted that
would affect the current transaction. This is the safest isolation level
and is the default.
- Repeatable
Read Data read by a current transaction cannot be changed by
another transaction until the current transaction finishes. Any type of
new data can be inserted during a transaction.
- Read
Committed A transaction cannot read data that is being
modified by another transaction that has not committed. This is the
default isolation level in Microsoft® SQL Server.
- Read
Uncommitted A transaction can read any data, even if it is
being modified by another transaction. This is the least safe isolation
level but allows the highest concurrency.
- Any
Any isolation level is supported. This setting is most commonly used by
downstream components to avoid conflicts. This setting is useful because
any downstream component must be configured with an isolation level that
is equal to or less than the isolation level of its immediate upstream component.
Therefore, a downstream component that has its isolation level configured
as Any always uses the same isolation level that its immediate upstream
component uses. If the root object in a transaction has its isolation
level configured to Any, its isolation level becomes Serialized.
How xml files and be read and write using dataset?.
DataSet exposes method like ReadXml and WriteXml to
read and write xml
What are the different rowversions available?
There are four types of Rowversions.
Current:
The current values for the row. This row version does not exist for rows with a
RowState of Deleted.
Default :
The row the default version for the current DataRowState. For a DataRowState
value of Added, Modified or Current, the default version is Current. For a
DataRowState of Deleted, the version is Original. For a DataRowState value of
Detached, the version is Proposed.
Original:
The row contains its original values.
Proposed:
The proposed values for the row. This row version exists during an edit
operation on a row, or for a row that is not part of a DataRowCollection
Explain acid properties?.
The term ACID conveys the role transactions play in
mission-critical applications. Coined by transaction processing pioneers, ACID
stands for atomicity, consistency, isolation, and durability.
These properties ensure predictable behavior,
reinforcing the role of transactions as all-or-none propositions designed to
reduce the management load when there are many variables.
Atomicity
A transaction is a unit of work in which a series of operations occur between
the BEGIN TRANSACTION and END TRANSACTION statements of an application. A
transaction executes exactly once and is atomic — all the work is done or none
of it is.
Operations associated with a transaction usually
share a common intent and are interdependent. By performing only a subset of
these operations, the system could compromise the overall intent of the
transaction. Atomicity eliminates the chance of processing a subset of
operations.
Consistency
A transaction is a unit of integrity because it preserves the consistency of
data, transforming one consistent state of data into another consistent state
of data.
Consistency requires that data bound by a
transaction be semantically preserved. Some of the responsibility for
maintaining consistency falls to the application developer who must make sure
that all known integrity constraints are enforced by the application. For
example, in developing an application that transfers money, you should avoid
arbitrarily moving decimal points during the transfer.
Isolation
A transaction is a unit of isolation — allowing concurrent transactions to
behave as though each were the only transaction running in the system.
Isolation requires that each transaction appear to
be the only transaction manipulating the data store, even though other
transactions may be running at the same time. A transaction should never see
the intermediate stages of another transaction.
Transactions attain the highest level of isolation
when they are serializable. At this level, the results obtained from a set of
concurrent transactions are identical to the results obtained by running each
transaction serially. Because a high degree of isolation can limit the number
of concurrent transactions, some applications reduce the isolation level in
exchange for better throughput.
Durability
A transaction is also a unit of recovery. If a transaction succeeds, the system
guarantees that its updates will persist, even if the computer crashes
immediately after the commit. Specialized logging allows the system's restart
procedure to complete unfinished operations, making the transaction durable.
Whate are different types of Commands available with DataAdapter ?
The SqlDataAdapter has SelectCommand, InsertCommand, DeleteCommand and
UpdateCommand
What is a Dataset?
Datasets are the result of bringing together ADO and XML. A dataset contains
one or more data of tabular XML, known as DataTables, these data can be treated
separately, or can have relationships defined between them. Indeed these
relationships give you ADO data SHAPING without needing to master the SHAPE
language, which many people are not comfortable with.
The dataset is a disconnected in-memory cache
database. The dataset object model looks like this:
Dataset
DataTableCollection
DataTable
DataView
DataRowCollection
DataRow
DataColumnCollection
DataColumn
ChildRelations
ParentRelations
Constraints
PrimaryKey
DataRelationCollection
Let’s take a look at each of these:
DataTableCollection: As we say that a DataSet is an
in-memory database. So it has this collection, which holds data from multiple
tables in a single DataSet object.
DataTable: In the DataTableCollection, we have
DataTable objects, which represents the individual tables of the dataset.
DataView: The way we have views in database, same
way we can have DataViews. We can use these DataViews to do Sort, filter data.
DataRowCollection: Similar to DataTableCollection,
to represent each row in each Table we have DataRowCollection.
DataRow: To represent each and every row of
the DataRowCollection, we have DataRows.
DataColumnCollection: Similar to
DataTableCollection, to represent each column in each Table we have
DataColumnCollection.
DataColumn: To represent each and every Column of the
DataColumnCollection, we have DataColumn.
PrimaryKey: Dataset defines Primary key for the
table and the primary key validation will take place without going to the
database.
Constraints: We can define various constraints on
the Tables, and can use Dataset.Tables(0).enforceConstraints. This will execute
all the constraints, whenever we enter data in DataTable.
DataRelationCollection: as we know that we can have
more than 1 table in the dataset, we can also define relationship between these
tables using this collection and maintain a parent-child relationship.
Explain the ADO . Net Architecture ( .Net Data
Provider)
ADO.Net is the data access model for .Net –based
applications. It can be used to access relational database systems such as SQL
SERVER 2000, Oracle, and many other data sources for which there is an OLD DB
or ODBC provider. To a certain extent, ADO.NET represents the latest evolution
of ADO technology. However, ADO.NET introduces some major changes and
innovations that are aimed at the loosely coupled and inherently disconnected –
nature of web applications.
A .Net Framework data provider is used to connecting
to a database, executing commands, and retrieving results. Those results are
either processed directly, or placed in an ADO.NET DataSet in order to be
exposed to the user in an ad-hoc manner, combined with data from multiple
sources, or remoted between tiers. The .NET Framework data provider is designed
to be lightweight, creating a minimal layer between the data source and your
code, increasing performance without sacrificing functionality.
Following are the 4 core objects of .Net Framework
Data provider:
- Connection:
Establishes a connection to a specific data source
- Command:
Executes a command against a data source. Exposes Parameters and can
execute within the scope of a Transaction from a Connection.
- DataReader:
Reads a forward-only, read-only stream of data from a data source.
- DataAdapter:
Populates a DataSet and resolves updates with the data source.
The .NET Framework includes the .NET Framework Data
Provider for SQL Server (for Microsoft SQL Server version 7.0 or later), the
.NET Framework Data Provider for OLE DB, and the .NET Framework Data Provider
for ODBC.
The .NET Framework Data Provider for SQL
Server: The .NET Framework Data Provider for SQL Server uses its own
protocol to communicate with SQL Server. It is lightweight and performs well
because it is optimized to access a SQL Server directly without adding an OLE
DB or Open Database Connectivity (ODBC) layer. The following illustration
contrasts the .NET Framework Data Provider for SQL Server with the .NET
Framework Data Provider for OLE DB. The .NET Framework Data Provider for OLE DB
communicates to an OLE DB data source through both the OLE DB Service
component, which provides connection pooling and transaction services, and the
OLE DB Provider for the data source
The .NET Framework Data Provider for OLE DB: The
.NET Framework Data Provider for OLE DB uses native OLE DB through COM
interoperability to enable data access. The .NET Framework Data Provider for
OLE DB supports both local and distributed transactions. For distributed
transactions, the .NET Framework Data Provider for OLE DB, by default,
automatically enlists in a transaction and obtains transaction details from Windows
2000 Component Services.
The .NET Framework Data Provider for ODBC: The .NET
Framework Data Provider for ODBC uses native ODBC Driver Manager (DM) through
COM interoperability to enable data access. The ODBC data provider supports
both local and distributed transactions. For distributed transactions, the ODBC
data provider, by default, automatically enlists in a transaction and obtains
transaction details from Windows 2000 Component Services.
The .NET Framework Data Provider for Oracle: The
.NET Framework Data Provider for Oracle enables data access to Oracle data
sources through Oracle client connectivity software. The data provider supports
Oracle client software version 8.1.7 and later. The data provider supports both
local and distributed transactions (the data provider automatically enlists in
existing distributed transactions, but does not currently support the
EnlistDistributedTransaction method).
The .NET Framework Data Provider for Oracle requires
that Oracle client software (version 8.1.7 or later) be installed on the system
before you can use it to connect to an Oracle data source.
.NET Framework Data Provider for Oracle classes are located in the
System.Data.OracleClient namespace and are contained in the
System.Data.OracleClient.dll assembly. You will need to reference both the
System.Data.dll and the System.Data.OracleClient.dll when compiling an
application that uses the data provider.
Choosing a .NET Framework Data Provider
.NET Framework Data Provider for SQL Server:
Recommended for middle-tier applications using Microsoft SQL Server 7.0 or
later. Recommended for single-tier applications using Microsoft Data Engine
(MSDE) or Microsoft SQL Server 7.0 or later.
Recommended over use of the OLE DB Provider for SQL Server (SQLOLEDB) with the
.NET Framework Data Provider for OLE DB. For Microsoft SQL Server version 6.5
and earlier, you must use the OLE DB Provider for SQL Server with the .NET
Framework Data Provider for OLE DB.
.NET Framework Data Provider for OLE DB: Recommended
for middle-tier applications using Microsoft SQL Server 6.5 or earlier, or any
OLE DB provider. For Microsoft SQL Server 7.0 or later, the .NET Framework Data
Provider for SQL Server is recommended. Recommended for single-tier
applications using Microsoft Access databases. Use of a Microsoft Access
database for a middle-tier application is not recommended.
.NET Framework Data Provider for ODBC: Recommended
for middle-tier applications using ODBC data sources. Recommended for
single-tier applications using ODBC data sources.
.NET Framework Data Provider for Oracle: Recommended
for middle-tier applications using Oracle data sources. Recommended for
single-tier applications using Oracle data sources. Supports Oracle client
software version 8.1.7 and later. The .NET Framework Data Provider for Oracle
classes are located in the System.Data.OracleClient namespace and are contained
in the System.Data.OracleClient.dll assembly. You need to reference both the
System.Data.dll and the System.Data.OracleClient.dll when compiling an application
that uses the data provider.
Can you explain the difference between an ADO.NET
Dataset and an ADO Recordset?
Let’s take a look at the differences between ADO Recordset and ADO.Net DataSet:
1. Table Collection: ADO Recordset provides the
ability to navigate through a single table of information. That table would
have been formed with a join of multiple tables and returning columns from
multiple tables. ADO.NET DataSet is capable of holding instances of multiple
tables. It has got a Table Collection, which holds multiple tables in it. If
the tables are having a relation, then it can be manipulated on a Parent-Child
relationship. It has the ability to support multiple tables with keys,
constraints and interconnected relationships. With this ability the DataSet can
be considered as a small, in-memory relational database cache.
2. Navigation: Navigation in ADO Recordset is based
on the cursor mode. Even though it is specified to be a client-side Recordset,
still the navigation pointer will move from one location to another on cursor
model only. ADO.NET DataSet is an entirely offline, in-memory, and cache of
data. All of its data is available all the time. At any time, we can retrieve
any row or column, constraints or relation simply by accessing it either ordinarily
or by retrieving it from a name-based collection.
3. Connectivity Model: The ADO Recordset was
originally designed without the ability to operate in a disconnected
environment. ADO.NET DataSet is specifically designed to be a disconnected
in-memory database. ADO.NET DataSet follows a pure disconnected connectivity
model and this gives it much more scalability and versatility in the amount of
things it can do and how easily it can do that.
4. Marshalling and Serialization: In COM, through
Marshalling, we can pass data from 1 COM component to another component at any
time. Marshalling involves copying and processing data so that a complex type
can appear to the receiving component the same as it appeared to the sending
component. Marshalling is an expensive operation. ADO.NET Dataset and DataTable
components support Remoting in the form of XML serialization. Rather than doing
expensive Marshalling, it uses XML and sent data across boundaries.
5. Firewalls and DCOM and Remoting: Those who have
worked with DCOM know that how difficult it is to marshal a DCOM component
across a router. People generally came up with workarounds to solve this issue.
ADO.NET DataSet uses Remoting, through which a DataSet / DataTable component
can be serialized into XML, sent across the wire to a new AppDomain, and then
Desterilized back to a fully functional DataSet. As the DataSet is completely
disconnected, and it has no dependency, we lose absolutely nothing by
serializing and transferring it through Remoting.
How do you handle data concurrency in .NET ?
One of the key features of the ADO.NET DataSet is
that it can be a self-contained and disconnected data store. It can contain the
schema and data from several rowsets in DataTable objects as well as
information about how to relate the DataTable objects-all in memory. The
DataSet neither knows nor cares where the data came from, nor does it need a
link to an underlying data source. Because it is data source agnostic you can
pass the DataSet around networks or even serialize it to XML and pass it across
the Internet without losing any of its features. However, in a disconnected
model, concurrency obviously becomes a much bigger problem than it is in a
connected model.
In this column, I'll explore how ADO.NET is equipped
to detect and handle concurrency violations. I'll begin by discussing scenarios
in which concurrency violations can occur using the ADO.NET disconnected model.
Then I will walk through an ASP.NET application that handles concurrency
violations by giving the user the choice to overwrite the changes or to refresh
the out-of-sync data and begin editing again. Because part of managing an
optimistic concurrency model can involve keeping a timestamp (rowversion) or
another type of flag that indicates when a row was last updated, I will show
how to implement this type of flag and how to maintain its value after each
database update.
Is Your Glass Half Full?
There are three common techniques for managing what
happens when users try to modify the same data at the same time: pessimistic,
optimistic, and last-in wins. They each handle concurrency issues differently.
The pessimistic approach says: "Nobody can
cause a concurrency violation with my data if I do not let them get at the data
while I have it." This tactic prevents concurrency in the first place but
it limits scalability because it prevents all concurrent access. Pessimistic
concurrency generally locks a row from the time it is retrieved until the time
updates are flushed to the database. Since this requires a connection to remain
open during the entire process, pessimistic concurrency cannot successfully be
implemented in a disconnected model like the ADO.NET DataSet, which opens a
connection only long enough to populate the DataSet then releases and closes,
so a database lock cannot be held.
Another technique for dealing with concurrency is
the last-in wins approach. This model is pretty straightforward and easy to
implement-whatever data modification was made last is what gets written to the
database. To implement this technique you only need to put the primary key
fields of the row in the UPDATE statement's WHERE clause. No matter what is
changed, the UPDATE statement will overwrite the changes with its own changes
since all it is looking for is the row that matches the primary key values.
Unlike the pessimistic model, the last-in wins approach allows users to read
the data while it is being edited on screen. However, problems can occur when
users try to modify the same data at the same time because users can overwrite
each other's changes without being notified of the collision. The last-in wins
approach does not detect or notify the user of violations because it does not
care. However the optimistic technique does detect violations. Contd....
In optimistic concurrency models, a row is only
locked during the update to the database. Therefore the data can be retrieved
and updated by other users at any time other than during the actual row update
operation. Optimistic concurrency allows the data to be read simultaneously by
multiple users and blocks other users less often than its pessimistic
counterpart, making it a good choice for ADO.NET. In optimistic models, it is
important to implement some type of concurrency violation detection that will
catch any additional attempt to modify records that have already been modified
but not committed. You can write your code to handle the violation by always
rejecting and canceling the change request or by overwriting the request based
on some business rules. Another way to handle the concurrency violation is to
let the user decide what to do. The sample application that is shown in Figure
1 illustrates some of the options that can be presented to the user in the
event of a concurrency violation.
Where Did My Changes Go?
When users are likely to overwrite each other's
changes, control mechanisms should be put in place. Otherwise, changes could be
lost. If the technique you're using is the last-in wins approach, then these
types of overwrites are entirely possible.For example, imagine Julie wants to
edit an employee's last name to correct the spelling. She navigates to a screen
which loads the employee's information into a DataSet and has it presented to
her in a Web page. Meanwhile, Scott is notified that the same employee's phone
extension has changed. While Julie is correcting the employee's last name,
Scott begins to correct his extension. Julie saves her changes first and then
Scott saves his.Assuming that the application uses the last-in wins approach
and updates the row using a SQL WHERE clause containing only the primary key's
value, and assuming a change to one column requires the entire row to be
updated, neither Julie nor Scott may immediatelyrealize the concurrency issue
that just occurred. In this particular situation, Julie's changes were
overwritten by Scott's changes because he saved last, and the last name
reverted to the misspelled version.
So as you can see, even though the users changed
different fields, their changes collided and caused Julie's changes to be lost.
Without some sort of concurrency detection and handling, these types of
overwrites can occur and even go unnoticed.When you run the sample application
included in this column's download, you should open two separate instances of
Microsoft® Internet Explorer. When I generated the conflict, I opened two
instances to simulate two users with two separate sessions so that a
concurrency violation would occur in the sample application. When you do this,
be careful not to use Ctrl+N because if you open one instance and then use the
Ctrl+N technique to open another instance, both windows will share the same
session.
Detecting Violations
The concurrency violation reported to the user in
Figure 1 demonstrates what can happen when multiple users edit the same data at
the same time. In Figure 1, the user attempted to modify the first name to
"Joe" but since someone else had already modified the last name to
"Fuller III," a concurrency violation was detected and reported.
ADO.NET detects a concurrency violation when a DataSet containing changed
values is passed to a SqlDataAdapter's Update method and no rows are actually
modified. Simply using the primary key (in this case the EmployeeID) in the
UPDATE statement's WHERE clause will not cause a violation to be detected
because it still updates the row (in fact, this technique has the same outcome
as the last-in wins technique). Instead, more conditions must be specified in
the WHERE clause in order for ADO.NET to detect the violation.
The key here is to make the WHERE clause explicit
enough so that it not only checks the primary key but that it also checks for
another appropriate condition. One way to accomplish this is to pass in all
modifiable fields to the WHERE clause in addition to the primary key. For
example, the application shown in Figure 1 could have its UPDATE statement look
like the stored procedure that's shown in Figure 2.
Notice that in the code in Figure 2 nullable columns
are also checked to see if the value passed in is NULL. This technique is not
only messy but it can be difficult to maintain by hand and it requires you to
test for a significant number of WHERE conditions just to update a row. This
yields the desired result of only updating rows where none of the values have
changed since the last time the user got the data, but there are other
techniques that do not require such a huge WHERE clause.
Another way to make sure that the row is only
updated if it has not been modified by another user since you got the data is
to add a timestamp column to the table. The SQL Server(tm) TIMESTAMP datatype
automatically updates itself with a new value every time a value in its row is
modified. This makes it a very simple and convenient tool to help detect
concurrency violations.
A third technique is to use a DATETIME column in
which to track changes to its row. In my sample application I added a column
called LastUpdateDateTime to the Employees table.
ALTER TABLE Employees ADD LastUpdateDateTime
DATETIME
There I update the value of the LastUpdateDateTime
field automatically in the UPDATE stored procedure using the built-in SQL
Server GETDATE function.
The binary TIMESTAMP column is simple to create and
use since it automatically regenerates its value each time its row is modified,
but since the DATETIME column technique is easier to display on screen and
demonstrate when the change was made, I chose it for my sample application.
Both of these are solid choices, but I prefer the TIMESTAMP technique since it
does not involve any additional code to update its value.
Retrieving Row Flags
One of the keys to implementing concurrency controls
is to update the timestamp or datetime field's value back into the DataSet. If
the same user wants to make more modifications, this updated value is reflected
in the DataSet so it can be used again. There are a few different ways to do
this. The fastest is using output parameters within the stored procedure. (This
should only return if @@ROWCOUNT equals 1.) The next fastest involves selecting
the row again after the UPDATE within the stored procedure. The slowest
involves selecting the row from another SQL statement or stored procedure from
the SqlDataAdapter's RowUpdated event.
I prefer to use the output parameter technique since
it is the fastest and incurs the least overhead. Using the RowUpdated event
works well, but it requires me to make a second call from the application to
the database. The following code snippet adds an output parameter to the
SqlCommand object that is used to update the Employee information:
oUpdCmd.Parameters.Add(new SqlParameter("@NewLastUpdateDateTime",
SqlDbType.DateTime, 8,
ParameterDirection.Output,
false, 0, 0, "LastUpdateDateTime",
DataRowVersion.Current, null));
oUpdCmd.UpdatedRowSource =
UpdateRowSource.OutputParameters;
The output parameter has its sourcecolumn and
sourceversion arguments set to point the output parameter's return value back
to the current value of the LastUpdateDateTime column of the DataSet. This way
the updated DATETIME value is retrieved and can be returned to the user's .aspx
page. Contd....
Saving Changes
Now that the Employees table has the tracking field
(LastUpdateDateTime) and the stored procedure has been created to use both the
primary key and the tracking field in the WHERE clause of the UPDATE statement,
let's take a look at the role of ADO.NET. In order to trap the event when the
user changes the values in the textboxes, I created an event handler for the
TextChanged event for each TextBox control:
private void txtLastName_TextChanged(object sender,
System.EventArgs e)
{
// Get the employee DataRow
(there is only 1 row, otherwise I could
// do a Find)
dsEmployee.EmployeeRow oEmpRow =
(dsEmployee.EmployeeRow)oDsEmployee.Employee.Rows[0];
oEmpRow.LastName =
txtLastName.Text;
// Save changes back to Session
Session["oDsEmployee"]
= oDsEmployee;
}
This event retrieves the row and sets the
appropriate field's value from the TextBox. (Another way of getting the changed
values is to grab them when the user clicks the Save button.) Each TextChanged
event executes after the Page_Load event fires on a postback, so assuming the
user changed the first and last names, when the user clicks the Save button,
the events could fire in this order: Page_Load, txtFirstName_TextChanged,
txtLastName_TextChanged, and btnSave_Click.
The Page_Load event grabs the row from the DataSet
in the Session object; the TextChanged events update the DataRow with the new
values; and the btnSave_Click event attempts to save the record to the
database. The btnSave_Click event calls the SaveEmployee method (shown in
Figure 3) and passes it a bLastInWins value of false since we want to attempt a
standard save first. If the SaveEmployee method detects that changes were made
to the row (using the HasChanges method on the DataSet, or alternatively using
the RowState property on the row), it creates an instance of the Employee class
and passes the DataSet to its SaveEmployee method. The Employee class could
live in a logical or physical middle tier. (I wanted to make this a separate
class so it would be easy to pull the code out and separate it from the
presentation logic.)
Notice that I did not use the GetChanges method to
pull out only the modified rows and pass them to the Employee object's Save
method. I skipped this step here since there is only one row. However, if there
were multiple rows in the DataSet's DataTable, it would be better to use the
GetChanges method to create a DataSet that contains only the modified rows.
If the save succeeds, the Employee.SaveEmployee
method returns a DataSet containing the modified row and its newly updated row
version flag (in this case, the LastUpdateDateTime field's value). This DataSet
is then merged into the original DataSet so that the LastUpdateDateTime field's
value can be updated in the original DataSet. This must be done because if the
user wants to make more changes she will need the current values from the
database merged back into the local DataSet and shown on screen. This includes
the LastUpdateDateTime value which is used in the WHERE clause. Without this
field's current value, a false concurrency violation would occur.
Reporting Violations
If a concurrency violation occurs, it will bubble up
and be caught by the exception handler shown in Figure 3 in the catch block for
DBConcurrencyException. This block calls the FillConcurrencyValues method,
which displays both the original values in the DataSet that were attempted to
be saved to the database and the values currently in the database. This method
is used merely to show the user why the violation occurred. Notice that the
exDBC variable is passed to the FillConcurrencyValues method. This instance of
the special database concurrency exception class (DBConcurrencyException)
contains the row where the violation occurred. When a concurrency violation
occurs, the screen is updated to look like Figure 1.
The DataSet not only stores the schema and the
current data, it also tracks changes that have been made to its data. It knows
which rows and columns have been modified and it keeps track of the before and
after versions of these values. When accessing a column's value via the
DataRow's indexer, in addition to the column index you can also specify a value
using the DataRowVersion enumerator. For example, after a user changes the
value of the last name of an employee, the following lines of C# code will
retrieve the original and current values stored in the LastName column:
string sLastName_Before =
oEmpRow["LastName", DataRowVersion.Original];
string sLastName_After =
oEmpRow["LastName", DataRowVersion.Current];
The FillConcurrencyValues method uses the row from
the DBConcurrencyException and gets a fresh copy of the same row from the
database. It then displays the values using the DataRowVersion enumerators to
show the original value of the row before the update and the value in the
database alongside the current values in the textboxes.
User's Choice
Once the user has been notified of the concurrency
issue, you could leave it up to her to decide how to handle it. Another
alternative is to code a specific way to deal with concurrency, such as always
handling the exception to let the user know (but refreshing the data from the
database). In this sample application I let the user decide what to do next.
She can either cancel changes, cancel and reload from the database, save
changes, or save anyway.
The option to cancel changes simply calls the
RejectChanges method of the DataSet and rebinds the DataSet to the controls in
the ASP.NET page. The RejectChanges method reverts the changes that the user
made back to its original state by setting all of the current field values to
the original field values. The option to cancel changes and reload the data
from the database also rejects the changes but additionally goes back to the
database via the Employee class in order to get a fresh copy of the data before
rebinding to the control on the ASP.NET page.
The option to save changes attempts to save the
changes but will fail if a concurrency violation is encountered. Finally, I
included a "save anyway" option. This option takes the values the
user attempted to save and uses the last-in wins technique, overwriting
whatever is in the database. It does this by calling a different command object
associated with a stored procedure that only uses the primary key field (EmployeeID)
in the WHERE clause of the UPDATE statement. This technique should be used with
caution as it will overwrite the record.
If you want a more automatic way of dealing with the
changes, you could get a fresh copy from the database. Then overwrite just the
fields that the current user modified, such as the Extension field. That way,
in the example I used the proper LastName would not be overwritten. Use this
with caution as well, however, because if the same field was modified by both
users, you may want to just back out or ask the user what to do next. What is
obvious here is that there are several ways to deal with concurrency
violations, each of which must be carefully weighed before you decide on the
one you will use in your application.
Wrapping It Up
Setting the SqlDataAdapter's ContinueUpdateOnError
property tells the SqlDataAdapter to either throw an exception when a
concurrency violation occurs or to skip the row that caused the violation and
to continue with the remaining updates. By setting this property to false (its
default value), it will throw an exception when it encounters a concurrency
violation. This technique is ideal when only saving a single row or when you
are attempting to save multiple rows and want them all to commit or all to fail.
I have split the topic of concurrency violation
management into two parts. Next time I will focus on what to do when multiple
rows could cause concurrency violations. I will also discuss how the
DataViewRowState enumerators can be used to show what changes have been made to
a DataSet.
How you will set the datarelation between two
columns?
ADO.NET provides DataRelation object to set relation
between two columns.It helps to enforce the following constraints,a
unique constraint, which guarantees that a column in the table contains
no duplicates and a foreign-key constraint,which can be used to maintain
referential integrity.A unique constraint is implemented either by simply
setting the Unique property of a data column to true, or by adding an
instance of the UniqueConstraint class to the DataRelation
object's ParentKeyConstraint. As part of the foreign-key constraint, you
can specify referential integrity rules that are applied at three
points,when a parent record is updated,when a parent record is deleted and when
a change is accepted or rejected.
C#
and VB.NET
Explain the differences between Server-side and
Client-side code?
Server side code executes on the server.For this to occur page has to be
submitted or posted back.Events fired by the controls are executed on the
server.Client side code executes in the browser of the client without
submitting the page.
e.g. In ASP.NET for webcontrols like asp:button the click event of the button
is executed on the server hence the event handler for the same in a part of the
code-behind (server-side code). Along the server-side code events one can also
attach client side events which are executed in the clients browser i.e.
javascript events.
How does VB.NET/C# achieve polymorphism?
Polymorphism is also achieved through interfaces.
Like abstract classes, interfaces also describe the methods that a class needs
to implement. The difference between abstract classes and interfaces is that
abstract classes always act as a base class of the related classes in the class
hierarchy. For example, consider a hierarchy-car and truck classes derived from
four-wheeler class; the classes two-wheeler and four-wheeler derived from an
abstract class vehicle. So, the class 'vehicle' is the base class in the class
hierarchy. On the other hand dissimilar classes can implement one interface.
For example, there is an interface that compares two objects. This interface
can be implemented by the classes like box, person and string, which are
unrelated to each other.
C# allows multiple interface inheritance. It means
that a class can implement more than one interface. The methods declared in an
interface are implicitly abstract. If a class implements an interface, it
becomes mandatory for the class to override all the methods declared in the
interface, otherwise the derived class would become abstract.
Can you explain what inheritance is and an example
of when you might use it?
The savingaccount class has two data members-accno that stores account number,
and trans that keeps track of the number of transactions. We can create an
object of savingaccount class as shown below.
savingaccount s = new savingaccount ( "Amar", 5600.00f ) ;
From the constructor of savingaccount class we have called the two-argument
constructor of the account class using the base keyword and passed the name and
balance to this constructor using which the data member's name and balance are
initialised.
We can write our own definition of a method that
already exists in a base class. This is called method overriding. We have
overridden the deposit( ) and withdraw( ) methods in the savingaccount class so
that we can make sure that each account maintains a minimum balance of Rs. 500
and the total number of transactions do not exceed 10. From these methods we
have called the base class's methods to update the balance using the base
keyword. We have also overridden the display( ) method to display additional
information, i.e. account number.
Working of currentaccount class is more or less
similar to that of savingaccount class.
Using the derived class's object, if we call a method that is not overridden in
the derived class, the base class method gets executed. Using derived class's
object we can call base class's methods, but the reverse is not allowed.
Unlike C++, C# does not support multiple
inheritance. So, in C# every class has exactly one base class.
Now, suppose we declare reference to the base class and store in it the address
of instance of derived class as shown below.
account
a1 = new savingaccount ( "Amar", 5600.00f ) ;
account a2 = new currentaccount ( "MyCompany Pvt. Ltd.",
126000.00f) ;
Such a situation arises when we have to decide at run-time a method of which
class in a class hierarchy should get called. Using a1 and a2, suppose we call
the method display( ), ideally the method of derived class should get called.
But it is the method of base class that gets called. This is because the
compiler considers the type of reference (account in this case) and resolves
the method call. So, to call the proper method we must make a small change in
our program. We must use the virtual keyword while defining the methods in base
class as shown below.
public
virtual void display( ) { }
We must declare the methods as virtual if they are going to be overridden in
derived class. To override a virtual method in derived classes we must use the
override keyword as given below.
public
override void display( ) { }
Now it is ensured that when we call the methods using upcasted reference, it is
the derived class's method that would get called. Actually, when we declare a
virtual method, while calling it, the compiler considers the contents of the
reference rather than its type.
If we don't want to override base class's virtual
method, we can declare it with new modifier in derived class. The new modifier
indicates that the method is new to this class and is not an override of a base
class method.
How would you implement inheritance using VB.NET/C#?
When we set out to implement a class using
inheritance, we must first start with an existing class from which we will
derive our new subclass. This existing class, or base class, may be part of the
.NET system class library framework, it may be part of some other application
or .NET assembly, or we may create it as part of our existing application. Once
we have a base class, we can then implement one or more subclasses based on
that base class. Each of our subclasses will automatically have all of the
methods, properties, and events of that base class ? including the
implementation behind each method, property, and event. Our subclass can add
new methods, properties, and events of its own - extending the original
interface with new functionality. Additionally, a subclass can replace the
methods and properties of the base class with its own new
implementation - effectively overriding the original behavior and replacing it
with new behaviors. Essentially inheritance is a way of merging functionality
from an existing class into our new subclass. Inheritance also defines rules
for how these methods, properties, and events can be merged. In VB.NET we can
use implements keyword for inheritance, while in C# we can use the sign ( :: )
between subclass and baseclass.
How is a property designated as read-only?
In VB.NET:
Private mPropertyName as DataType
Public ReadOnly Property PropertyName() As DataType
Get Return mPropertyName
End Get
End Property
In C#
Private DataType mPropertyName;
public returntype PropertyName
{
get{
//property implementation goes here
return mPropertyName;
}
// Do not
write the set implementation
}
What is hiding in CSharp ?
Hiding is also called as Shadowing. This is the
concept of Overriding the methods. It is a concept used in the Object Oriented
Programming.
E.g.
public class ClassA {
public virtual void MethodA() {
Trace.WriteLine("ClassA Method");
}
}
public class ClassB : ClassA {
public new void MethodA() {
Trace.WriteLine("SubClass ClassB Method");
}
}
public class TopLevel {
static void Main(string[] args) {
TextWriter tw = Console.Out;
Trace.Listeners.Add(new TextWriterTraceListener(tw));
ClassA obj = new ClassB();
obj.MethodA(); // Outputs “Class A Method"
ClassB obj1 = new ClassB();
obj.MethodA(); // Outputs “SubClass ClassB Method”
}
}
What is the difference between an XML
"Fragment" and an XML "Document."
An XML fragment is an XML document with no single
top-level root element. To put it simple it is a part (fragment) of a
well-formed xml document. (node) Where as a well-formed xml document must have
only one root element.
What does it meant to say “the canonical” form of
XML?
"The purpose of Canonical XML is to define a standard format for an XML
document. Canonical XML is a very strict XML syntax, which lets documents in
canonical XML be compared directly.
Using this strict syntax makes it easier to see whether two XML documents are
the same. For example, a section of text in one document might read Black &
White, whereas the same section of text might read Black & White in another
document, and even in another. If you compare those three documents byte by
byte, they'll be different. But if you write them all in canonical XML, which
specifies every aspect of the syntax you can use, these three documents would
all have the same version of this text (which would be Black & White) and
could be compared without problem.
This Comparison is especially critical when xml documents are digitally signed.
The digital signal may be interpreted in different way and the document may be
rejected.
Why is the XML InfoSet specification different from the Xml DOM? What
does the InfoSet attempt to solve?
"The XML Information Set (Infoset) defines a data model for XML. The
Infoset describes the abstract representation of an XML Document. Infoset is
the generalized representation of the XML Document, which is primarily meant to
act as a set of definitions used by XML technologies to formally describe what
parts of an XML document they operate upon.
The Document Object Model (DOM) is one technology for representing an XML
Document in memory and to programmatically read, modify and manipulate a xml
document.
Infoset helps defining generalized standards on how to use XML that is not
dependent or tied to a particular XML specification or API. The Infoset tells
us what part of XML Document should be considered as significant information.
Contrast DTDs versus XSDs. What are their
similarities and differences? Which is preferred and why?
Document Type Definition (DTD) describes a model or
set of rules for an XML document. XML Schema Definition (XSD) also describes
the structure of an XML document but XSDs are much more powerful.
The disadvantage with the Document Type Definition is it doesn’t support data
types beyond the basic 10 primitive types. It cannot properly define the type
of data contained by the tag.
An Xml Schema provides an Object Oriented approach to defining the format of an
xml document. The Xml schema support most basic programming types like integer,
byte, string, float etc., We can also define complex types of our own which can
be used to define a xml document.
Xml Schemas are always preferred over DTDs as a document can be more precisely
defined using the XML Schemas because of its rich support for data
representation.
Speaking of Boolean data types, what's different
between C# and C/C++?
There's no conversion between 0 and false, as well
as any other number and true, like in C/C++.
How do you convert a string into an integer in .NET?
Int32.Parse(string)
Can you declare a C++ type destructor in C# like
~MyClass()?
Yes, but what's the point, since it will call
Finalize(), and Finalize() has no guarantees when the memory will be cleaned
up, plus, it introduces additional load on the garbage collector.
What's different about namespace declaration when
comparing that to package declaration in Java?
No semicolon.
What's the difference between const and readonly?
The readonly keyword is different from the const keyword. A const field can
only be initialized at the declaration of the field. A readonly field can be
initialized either at the declaration or in a constructor. Therefore, readonly
fields can have different values depending on the constructor used. Also, while
a const field is a compile-time constant, the readonly field can be used for
runtime constants as in the following example:
public static readonly uint l1 = (uint) DateTime.Now.Ticks;
What does \a character do?
On most systems, produces a rather annoying beep.
Can you create enumerated data types in C#?
Yes.
What's different about switch statements in C#?
No fall-throughs allowed.
What happens when you encounter a continue statement
inside the for loop?
The code for the rest of the loop is ignored, the
control is transferred back to the beginning of the loop.
How can you sort the elements of the array in
descending order?
By calling Sort() and then Reverse() methods.
Will finally block get executed if the exception had
not occurred?
Yes.
What's the C# equivalent of C++ catch (…), which was
a catch-all statement for any possible exception?
A catch block that catches the exception of type
System.Exception. You can also omit the parameter data type in this case and
just write catch {}.
Can multiple catch blocks be executed?
No, once the proper catch code fires off, the control is transferred to the
finally block (if there are any), and then whatever follows the finally block.
Why is it a bad idea to throw your own exceptions?
Well, if at that point you know that an error has
occurred, then why not write the proper code to handle that error instead of
passing a new Exception object to the catch block? Throwing your own exceptions
signifies some design flaws in the project.
What's the difference between // comments, /* */
comments and /// comments?
Single-line, multi-line and XML documentation
comments.
How do you generate documentation from the C# file
commented properly with a command-line compiler?
Compile it with a /doc switch.
Can you change the value of a variable while
debugging a C# application?
Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.
What's the implicit name of the parameter that gets
passed into the class' set method?
Value, and it's datatype depends on whatever
variable we're changing.
How do you inherit from a class in C#?
Place a colon and then the name of the base class. Notice that it's double
colon in C++.
Does C# support multiple inheritance?
No, use interfaces instead.
So how do you retrieve the customized properties of
a .NET application from XML .config file? Can you automate this process?
Initialize an instance of AppSettingsReader class.
Call the GetValue method of AppSettingsReader class, passing in the name of the
property and the type expected. Assign the result to the appropriate variable.
In Visual Studio yes, use Dynamic Properties for automatic .config creation,
storage and retrieval.
Why is it not a good idea to insert code into
InitializeComponent method when working with Visual Studio?
The designer will likely through it away, most of
the code inside InitializeComponent is auto-generated.
Where do you add an event handler?
It's the Attributesproperty, the Add function inside that property.
e.g. btnSubmit.Attributes.Add(""onMouseOver"",""someClientCode();"")
What are jagged array?
First lets us answer the question that what an array
is?
The dictionary meaning of array is an orderly arrangement or sequential
arrangement of elements.
In computer science term:
An array is a data structure that contains a number of variables, which are
accessed through computed indices. The variables contained in an array, also
called the elements of the array, are all of the same type, and this type is
called the element type of the array.
An array has a rank that determines the number of
indices associated with each array element. The rank of an array is also
referred to as the dimensions of the array. An array with a rank of one is
called a single-dimensional array. An array with a rank greater than one is
called a multi-dimensional array. Specific sized multidimensional arrays are
often referred to as two-dimensional arrays, three-dimensional arrays, and so
on.
Now let us answer What are jagged arrays?
A jagged array is an array whose elements are
arrays. The elements of jagged array can be of different dimensions and sizes.
A jagged array is sometimes called as “array-of-arrays”. It is called jagged
because each of its rows is of different size so the final or graphical
representation is not a square.
When you create a jagged array you declare the
number of rows in your array. Each row will hold an array that will be on any
length. Before filling the values in the inner arrays you must declare them.
Jagged array declaration in C#:
For e.g. : int [] [] myJaggedArray = new int
[3][];
Declaration of inner arrays:
myJaggedArray[0] = new int[5] ; // First inner array will be
of length 5.
myJaggedArray[1] = new int[4] ; // Second inner array will be of
length 4.
myJaggedArray[2] = new int[3] ; // Third inner array will be
of length 3.
Now to access third element of second row we write:
int value = myJaggedArray[1][2];
Note that while declaring the array the second
dimension is not supplied because this you will declare later on in the code.
Jagged array are created out of single dimensional
arrays so be careful while using them. Don’t confuse it with multi-dimensional
arrays because unlike them jagged arrays are not rectangular arrays.
For more information on arrays:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/csref/html/vclrfarrayspg.asp
What is a delegate, why should you use it and how do
you call it ?
A delegate is a reference type that refers to a
Shared method of a type or to an instance method of an object. Delegate is like
a function pointer in C and C++. Pointers are used to store the address
of a thing. Delegate lets some other code call your function without needing to
know where your function is actually located. All events in .NET actually use
delegates in the background to wire up events. Events are really just a
modified form of a delegate.
It should give you an idea of some different areas in which delegates may be
appropriate:
- They
enable callback functionality in multi-tier applications as demonstrated
in the examples above. <o:p></o:p>
- The
CacheItemRemoveCallback delegate can be used in ASP.NET to keep cached
information up to date. When the cached information is removed for any
reason, the associated callback is exercised and could contain a reload of
the cached information. <o:p></o:p>
- Use
delegates to facilitate asynchronous processing for methods that do not
offer asynchronous behavior.
- Events
use delegates so clients can give the application events to call when the
event is fired. Exposing custom events within your applications requires
the use of delegates.
How does the XmlSerializer work?
XmlSerializer in the .NET Framework is a great tool to convert Xml into runtime
objects and vice versa
If you define integer variable and a object variable
and a structure then how those will be plotted in memory.
Integer , structure – System.ValueType --
Allocated memory on stack , infact integer is primitive type recognized and
allocated memory by compiler itself .
Infact , System.Int32 definition is as follows :
[C#]
[Serializable]
public struct Int32 : IComparable, IFormattable, IConvertible
So , it’s a struct by definition , which is the same
case with various other value types .
Object – Base class , that is by default reference
type , so at runtime JIT compiler allocates memory on the “Heap” Data structure
.
Reference types are defined as class , derived
directly or indirectly by System.ReferenceType
