.Netfx Qs?

(B)What is a IL?

Twist :- What is MSIL or CIL , What is JIT?

(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL

(Common Intermediate Language). All .NET source code is compiled to IL. This 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.

(B)What is a CLR?

Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework.

All Languages have runtime and its the responsibility of the runtime to take care of the code

execution of the program. For example VC++ has MSCRT40.DLL,VB6 has MSVBVM60.DLL,

Java has Java Virtual Machine etc. Similarly .NET has CLR. Following are the responsibilities of

CLR

Garbage Collection :- CLR automatically manages memory thus eliminating

memory leaks. When objects are not referred GC automatically releases those

memories thus providing efficient memory management.

Code Access Security :- CAS grants rights to program depending on the security

configuration of the machine. Example the program has rights to edit or create

a new file but the security configuration of machine does not allow the program

to delete a file. CAS will take care that the code runs under the environment of

machines security configuration.

Code Verification :- This ensures proper code execution and type safety while

the code runs. It prevents the source code to perform illegal operation such as

accessing invalid memory locations etc.

IL( Intermediate language )-to-native translators and optimizer’s :- CLR uses

JIT and compiles the IL code to machine code and then executes. CLR also

determines depending on platform what is optimized way of running the IL

code.

(B)What is a CTS?

In order that two language communicate smoothly CLR has CTS (Common Type System).Example

in VB you have “Integer” and in C++ you have “long” these datatypes are not compatible so the

interfacing between them is very complicated. In order to able that two different languages can

1. Basic .NET Framework

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communicate Microsoft introduced Common Type System. So “Integer” datatype in VB6 and

“int” datatype in C++ will convert it to System.int32 which is datatype of CTS. CLS which is

covered in the coming question is subset of CTS.

Note: If you have undergone COM programming period interfacing VB6 application with

VC++ application was a real pain as the datatype of both languages did not have a

common ground where they can come and interface, by having CTS interfacing is smooth.

(B)What is a CLS(Common Language Specification)?

This is a subset of the CTS which all .NET languages are expected to support. It was always a

dream of Microsoft to unite all different languages in to one umbrella and CLS is one step

towards that. Microsoft has defined CLS which are nothing but guidelines that language to follow

so that it can communicate with other .NET languages in a seamless manner.

(B)What is a Managed Code?

Managed code runs inside the environment of CLR i.e. .NET runtime. In short all IL are managed

code. But if you are using some third party software example VB6 or VC++ component they are

unmanaged code as .NET runtime (CLR) does not have control over the source code execution

of the language.

(B)What is a Assembly?

Assembly is unit of deployment like EXE or a DLL.

An assembly consists of one or more files (dlls, exe’s, html files etc.), and

represents a group of resources, type definitions, and implementations of those

types. An assembly may also contain references to other assemblies. These

resources, types and references are described in a block of data called a manifest.

The manifest is part of the assembly, thus making the assembly self-describing.

An assembly is completely self-describing.An assembly contains metadata

information, which is used by the CLR for everything from type checking and

security to actually invoking the components methods. As all information is in the

assembly itself, it is independent of registry. This is the basic advantage as

compared to COM where the version was stored in registry.

Multiple versions can be deployed side by side in different folders. These

different versions can execute at the same time without interfering with each

other. Assemblies can be private or shared. For private assembly deployment, the

assembly is copied to the same directory as the client program that references

it. No registration is needed, and no fancy installation program is required.

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When the component is removed, no registry cleanup is needed, and no uninstall

program is required. Just delete it from the hard drive.

In shared assembly deployment, an assembly is installed in the Global Assembly

Cache (or GAC). The GAC contains shared assemblies that are

globally accessible to all .NET applications on the machine.

(A) What are the different types of Assembly?

There are two types of assembly Private and Public assembly. A private assembly is normally used

by a single application, and is stored in the application’s directory, or a sub-directory beneath. A

shared assembly is normally stored in the global assembly cache, which is a repository of assemblies

maintained by the .NET runtime. Shared assemblies are usually libraries of code which many

applications will find useful, e.g. Crystal report classes which will be used by all application for

Reports.

(B) What is NameSpace?

Namespace has two basic functionality :-

NameSpace Logically group types, example System.Web.UI logically groups

our UI related features.

In Object Oriented world many times its possible that programmers will use the

same class name.By qualifying NameSpace with classname this collision is able to

be removed.

(B) What is Difference between NameSpace and Assembly?

Following are the differences between namespace and assembly :

Assembly is physical grouping of logical units. Namespace logically groups

classes.

Namespace can span multiple assembly.

(A)If you want to view a Assembly how do you go about it ?

Twist : What is ILDASM ?

When it comes to understanding of internals nothing can beat ILDASM. ILDASM basically converts

the whole exe or dll in to IL code. To run ILDASM you have to go to “C:\Program Files\Microsoft

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Visual Studio .NET 2003\SDK\v1.1\Bin”. Note that i had v1.1 you have to probably change it

depending on the type of framework version you have.

If you run IDASM.EXE from the path you will be popped with the IDASM exe program as

shown in figure ILDASM. Click on file and browse to the respective directory for the DLL

whose assembly you want to view. After you select the DLL you will be popped with a tree view

details of the DLL as shown in figure ILDASM. On double clicking on manifest you will be able

to view details of assembly, internal IL code etc as shown in Figure Manifest View.

Note : The version number are in the manifest itself which is defined with the DLL or

EXE thus making deployment much easier as compared to COM where the information

was stored in registry. Note the version information in Figure Manifest view.

You can expand the tree for detail information regarding the DLL like methods etc.

Figure:- 1.1 ILDASM

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Figure :- 1.2 Manifest View

(A) What is Manifest?

Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the

following things (See Figure Manifest View for more details):

Version of assembly

Security identity

Scope of the assembly

Resolve references to resources and classes.

The assembly manifest can be stored in either a PE file (an .exe or .dll) with

Microsoft intermediate language (MSIL) code or in a stand-alone PE file that

contains only assembly manifest information.

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(B)Where is version information stored of an assembly ?

Version information is stored in assembly in manifest.

(I)Is versioning applicable to private assemblies?

Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in

their individual folders.

(B) What is GAC ?

Twist :- What are situations when you register .NET assembly in GAC ?

GAC (Global Assembly Cache) is used where shared .NET assembly reside. GAC is used in the

following situations :-

If the application has to be shared among several application.

If the assembly has some special security requirements like only administrators

can remove the assembly. If the assembly is private then a simple delete of

assembly the assembly file will remove the assembly.

Note :- Registering .NET assembly in GAC can lead to the old problem of DLL hell,

where COM version was stored in central registry. So GAC should be used when absolutely

necessary.

(I) What is the concept of strong names ?

Twist :- How do we generate strong names or what is the process of generating strong

names, What is use the of SN.EXE , How do we apply strong names to assembly, How

do you sign an assembly?

Strong name is similar to GUID(It is supposed to be unique in space and time) in COM

components.Strong Name is only needed when we need to deploy assembly in GAC. Strong

Names helps GAC to differentiate between two versions. Strong names use public key cryptography

(PKC) to ensure that no one can spoof it.PKC use public key and private key concept.

Following are the step to generate a strong name and sign a assembly :-

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Go to “Visual Studio Command Prompt”. See below figure “Visual studio

Command Prompt”. Note the samples are compiled in 2005 but 2003 users do

not have to worry about it. Same type of command prompt will be seen in

2003 also.

Figure :- 1.3 Visual Studio Command Prompt

After you are in command prompt type sn.exe -k “c:\test.snk”.

Figure :- 1.4 Running SN.EXE

Figure :- 1.5 Successful output of SN.EXE

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Figure :- 1.6 Sample view of test.snk file

After generation of the file you can view the SNK file in a simple notepad.

After the SNK file is generated its time to sign the project with this SNK file.

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Figure:- 1.7 Click on project and then click on “classlibrary1 properties” menu to sign the assembly

Click on project — properties and the browse the SNK file to the respective

folder and compile the project.

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Figure :- 1.8 Click on Use a key file to sign the assembly with strong name

(I)How to add and remove an assembly from GAC?

There are two ways to install .NET assembly in GAC:-

Using Microsoft Installer Package. You can get download of installer from

http://www.microsoft.com.

Using Gacutil. Goto “Visual Studio Command Prompt” and type “gacutil –i

(assembly_name)”, where (assembly_name) is the DLL name of the project.

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(B) What is Delay signing ?

During development process you will need strong name keys to be exposed to developer which

is not a good practice from security aspect point of view.In such situations you can assign the key

later on and during development you an use delay signing

Following is process to delay sign an assembly:

First obtain your string name keys using SN.EXE.

Annotate the source code for the assembly with two custom attributes from

System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file

containing the public key as a parameter to its constructor. AssemblyDelaySignAttribute,

which indicates that delay signing, is being used by passing true as a parameter to its

constructor. For example as shown below:

[Visual Basic]

<Assembly:AssemblyKeyFileAttribute(“myKey.snk”)>

<Assembly:AssemblyDelaySignAttribute(true)>

[C#]

[assembly:AssemblyKeyFileAttribute(“myKey.snk”)]

[assembly:AssemblyDelaySignAttribute(true)]

The compiler inserts the public key into the assembly manifest and reserves space in the PE file for

the full strong name signature. The real public key must be stored while the assembly is built so

that other assemblies that reference this assembly can obtain the key to store in their own assembly

reference.

Because the assembly does not have a valid strong name signature, the verification of

that signature must be turned off. You can do this by using the –Vr option with the

Strong Name tool.The following example turns off verification for an assembly called

myAssembly.dll.

Sn –Vr myAssembly.dll

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Just before shipping, you submit the assembly to your organization’s signing authority

for the actual strong name signing using the –R option with the Strong Name tool.

The following example signs an assembly called myAssembly.dll with a strong name

using the sgKey.snk key pair.

Sn -R myAssembly.dll sgKey.snk

(B)What is garbage collection?

Garbage collection is a CLR feature which automatically manages memory. Programmers forget

to release the objects while coding ….. Laziness (Remember in VB6 where one of the good

practices is to set object to nothing). CLR automatically releases objects when they are no longer in

use and refernced. CLR runs on non-deterministic to see the unused objects and cleans them. One

side effect of this non-deterministic feature is that we cannot assume an object is destroyed when

it goes out of the scope of a function. Therefore, we should not put code into a class destructor

to release resources.

(I) Can we force garbage collector to run ?

System.GC.Collect() forces garbage collector to run. This is not recommended but can be used if

situations arises.

(B)What is reflection?

All .NET assemblies have metadata information stored about the types defined in modules. This

metadata information can be accessed by mechanism called as “Reflection”.System. Reflection

can be used to browse through the metadata information.

Using reflection you can also dynamically invoke methods using System.Type.Invokemember.

Below is sample source code if needed you can also get this code from CD provided, go to

“Source code” folder in “Reflection Sample” folder.

Public Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As

System.EventArgs) Handles MyBase.Load

Dim Pobjtype As Type

Dim PobjObject As Object

Dim PobjButtons As New Windows.Forms.Button()

Pobjtype = PobjButtons.GetType()

For Each PobjObject In Pobjtype.GetMembers

LstDisplay.Items.Add(PobjObject.ToString())

Next

End Sub

End Class

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Note :- Sample source code are compiled using VB.NET 2005.

Figure:- 1.9 Sample reflection display

Sample source code uses reflection to browse through “Button” class of “Windows.Forms”. If

you compile and run the program following is output as shown in “Sample Reflection Display”.

Using reflection you can also dynamically invoke a method using “System.Type.InvokeMember”.

Note :- System.Type.InvokeMember is left as homework for readers. Believe me you will

enjoy doing it yourself and the concept of reflection will be clearer.

(P)What are different types of JIT ?

Note :- This question can only be asked when the interviewer does not know what he wants.

It was asked to me in one of interview and for 15 minutes he was roaming around the

same question in order to get answer from me (requirement was for a simple database

project). Beware of such companies and interviewers you can land up no where.

JIT compiler is a part of the runtime execution environment.

In Microsoft .NET there are three types of JIT compilers:

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Pre-JIT :- Pre-JIT compiles complete source code into native code in a single

compilation cycle. This is done at the time of deployment of the application.

Econo-JIT :- Econo-JIT compiles only those methods that are called at runtime.

However, these compiled methods are removed when they are not required.

Normal-JIT :- Normal-JIT compiles only those methods that are called at runtime.

These methods are compiled the first time they are called, and then they are stored in

cache. When the same methods are called again, the compiled code from cache is

used for execution.

(B) What are Value types and Reference types ?

Value types directly contain their data which are either allocated on the stack or allocated in-line in

a structure.

Reference types store a reference to the value’s memory address, and are allocated on the heap.

Reference types can be self-describing types, pointer types, or interface types.

Variables that are value types each have their own copy of the data, and therefore operations on

one variable do not affect other variables. Variables that are reference types can refer to the same

object; therefore, operations on one variable can affect the same object referred to by another

variable. All types derive from the System.Object base type.

(B) What is concept of Boxing and Unboxing ?

Boxing permits any value type to be implicitly converted to type object or to any interface type

implemented by value type. Boxing is a process in which object instances are created and copy

values in to that instance.

Unboxing is vice versa of boxing operation where the value is copied from the instance in to

appropriate storage location.

Below is sample code of boxing and unboxing where integer data type is converted in to object

and then vice versa.

Dim x As Integer

Dim y As Object

x = 10

‘ boxing process

y = x

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‘ unboxing process

x = y

(B) What is the difference between VB.NET and C# ?

Well this is the most debatable issue in .NET community and people treat there languages like

religion. Its a subjective matter which language is best. Some like VB.NET’s natural style and some

like professional and terse C# syntaxes. Both use the same framework and speed is also very much

equivalents. But still let’s list down some major differences between them :-

Advantages VB.NET :-

Has support for optional parameters which makes COM interoperability much easy.

With Option Strict off late binding is supported.Legacy VB functionalities can be

used by using Microsoft.VisualBasic namespace.

Has the WITH construct which is not in C#.

The VB.NET part of Visual Studio .NET compiles your code in the background.

While this is considered an advantage for small projects, people creating very large

projects have found that the IDE slows down considerably as the project gets larger.

Advantages of C#

XML documentation is generated from source code but this is now been incorporated

in Whidbey.

Operator overloading which is not in current VB.NET but is been introduced in

Whidbey.

Use of this statement makes unmanaged resource disposal simple.

Access to Unsafe code. This allows pointer arithmetic etc, and can improve

performance in some situations. However, it is not to be used lightly, as a lot of the

normal safety of C# is lost (as the name implies).This is the major difference that you

can access unmanaged code in C# and not in VB.NET.

* How much ever this book tries it can not match the huge variations of questions that have

been asked in.NET interviews.But note there will be variations and they will map to some

question of this book.

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(I)What is the difference between System exceptions and Application

exceptions?

All exception derives from Exception Base class. Exceptions can be generated programmatically

or can be generated by system. Application Exception serves as the base class for all applicationspecific

exception classes. It derives from Exception but does not provide any extended functionality.

You should derive your custom application exceptions from Application Exception.

Application exception is used when we want to define user defined exception, while system

exception is all which is defined by .NET.

Figure :- 1.10 Exception Hierarchy

Note:- Frankly I have always relied on using Microsoft exception application blocks. As

such I have never used application exception; I think most of the work is done using System

exception classes.

(I)What is CODE Access security?

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CAS is part of .NET security model that determines whether or not a piece of code is allowed to

run and what resources it can use while running. Example CAS will allow an application to read

but not to write and delete a file or a resource from a folder..

(I)What is a satellite assembly?

Refer Localization chapter for more details

(A)How to prevent my .NET DLL to be decompiled?

By design .NET embeds rich Meta data inside the executable code using MSIL. Any one can easily

decompile your DLL back using tools like ILDASM (owned by Microsoft) or Reflector for

.NET which is a third party. Secondly there are many third party tools which make this decompiling

process a click away. So any one can easily look in to your assemblies and reverse engineer them

back in to actual source code and understand some real good logic which can make it easy to

crack your application.

The process by which you can stop this reverse engineering is using “obfuscation”. It’s a technique

which will foil the decompilers. There are many third parties (XenoCode, Demeanor for .NET)

which provide .NET obfuscation solution. Microsoft includes one that is Dotfuscator Community

Edition with Visual Studio.NET.

Note: – I leave this as homework to reader’s compile, a DLL obfuscate it using

“Dotfuscator Community Edition” which comes with Visual Studio.NET and try viewing

the same using ILDASM.

(I) What is the difference between Convert.toString and .toString()

method ?

Just to give an understanding of what the above question means seethe below code.

int i =0;

MessageBox.Show(i.ToString());

MessageBox.Show(Convert.ToString(i));

We can convert the integer “i” using “i.ToString()” or “Convert.ToString” so what’s the difference.

The basic difference between them is “Convert” function handles NULLS while “i.ToString()”

does not it will throw a NULL reference exception error. So as good coding practice using

“convert” is always safe.

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(A) What is Native Image Generator (Ngen.exe)?

The Native Image Generator utility (Ngen.exe) allows you to run the JIT compiler on your assembly’s

MSIL and generate native machine code which is cached to disk. After the image is created .NET

runtime will use the image to run the code rather than from the hard disk. Running Ngen.exe on

an assembly potentially allows the assembly to load and execute faster, because it restores code

and data structures from the native image cache rather than generating them dynamically.

Below are some points to be remembered for Native Image Generator:-

Native images load faster than MSIL because JIT compilation and type-safety verification

is eliminated.

If you are sharing code between process Ngen.exe improves the performance

significantly. As Native image generated Windows PE file so a single DLL file can be

shared across applications. By contrast JIT produced code are private to an assembly

and can not be shared.

Native images enable code sharing between processes.

Native images require more storage space and more time to generate.

Startup time performance improves lot. We can get considerable gains when applications

share component assemblies because after the first application has been started the

shared components are already loaded for subsequent applications. If assemblies in

an application must be loaded from the hard disk, does not benefit as much from

native images because the hard disk access time shadows everything.

Assemblies in GAC do not benefit from Native image generator as the loader performs

extra validation on the strong named assemblies thus shadowing the benefits of Native

Image Generator.

If any of the assemblies change then Native image should also be updated.

You should have administrative privilege for running Ngen.exe.

While this can fasten your application startup times as the code is statically compiled

but it can be somewhat slower than the code generated dynamically by the JIT compiler.

So you need to compare how the whole application performance with Ngen.exe and

with out it.

To run Ngen.exe, use the following command line.

ngen.exe install <assemblyname>

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This will synchronously precompile the specified assembly and all of its dependencies. The generated

native images are stored in the native image cache.

In .NET Framework 2.0 there is a service (.NET Runtime Optimization Service) which can

precompile managed assemblies in the background. You can schedule your assemblies to be

precompiled asynchronously by queueing them up with the NGEN Service. Use the following

command line.

ngen.exe install <assemblyname> /queue:<priority>

Assemblies which are critical to your application’s start up time should either be precompiled

synchronously or asynchronously with priority 1. Priority 1 and 2 assemblies are precompiled

aggressively while Priority 3 assemblies are only precompiled during machine idle-time.

Synchronously precompiling your critical assemblies guarantees that the native images will be

available prior to the first time your end user launches the application but increases the time taken

to run your application’s set up program.

You can uninstall an assembly and its dependencies (if no other assemblies are dependent on

them) from the native image cache by running the following command.

ngen.exe uninstall <assemblyname>

Native images created using Ngen.exe cannot be deployed; instead they need to be created on the

end user’s machine. These commands therefore need to be issued as part of the application’s

setup program. Visual Studio .NET can be used to implement this behavior by defining custom

actions in a Microsoft Installer (MSI) package.

Note: – One of the things the interviewer will expect to be answered is what scenario will

use a Native Image generator. Best is to say that we first need to test the application

performance with Native Image and with out it and then make a decision.

(A) We have two version of the same assembly in GAC? I want my client

to make choice of which assembly to choose?

Note: – I really want to explain this in depth for two reasons. First I have seen this

question been frequently asked and second it’s of real practical importance. I have faced this

in every of my .NET projects…So let’s try to get this fundamental not in our brain but in

our heart.

OK first let’s try to understand what the interviewer is talking about. Let’s say you have made an

application and its using a DLL which is present in GAC. Now for some reason you make second

version of the same DLL and put it in GAC. Now which DLL does the application refer? Ok by

default it always refers the latest one. But you want that it should actually use the older version.

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So first we answer in short. You need to specify “bindingRedirect” in your config file. For instance

in the below case “ClassLibraryVersion” has two versions “1.1.1830.10493” and “1.0.1830.10461”

from which “1.1.1830.10493” is the recent version. But using the bindingRedirect we can specify

saying “1.0.1830.10461” is the new version. So the client will not use “1.1.1830.10493”.

<configuration>

<runtime>

<assemblyBinding xmlns=”urn:schemas-microsoft-com:asm.v1″>

<dependentAssembly>

<assemblyIdentity name=”ClassLibraryVersion”

publicKeyToken=”b035c4774706cc72″

culture=”neutral”/>

<bindingRedirect oldVersion= “1.1.1830.10493”

newVersion= “1.0.1830.10461”/>

</dependentAssembly>

</assemblyBinding>

</runtime>

</configuration>

Ok now I will try to answer it in long way by doing a small sample project. Again this project will

be done using C#. So in CD you can find the “Versioning” project. Below is the solution display,

it has two projects one the windows client project ( “WindowsVersioningCSharp” ) and second

the class library project ( “ClassLibraryVersion” ) which will be installed in GAC with two versions.

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Figure 1.11: – Solution files for the versioning project.

Our first primary goal is to put two different versions of the same DLL in GAC. So let’s make a

walk through of “ClassLibraryVersion” project. It’s a very simple class which has “Version” function

which just sends a string “This is old Version”. Second we will also just ensure that the assembly

version is “1.0” in the “AssemblyInfo.cs”.

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Figure 1.12 : – Assembly Version 1.0

Second in order that we can put a DLL in GAC we need to create generate strong names and

assign the same to the class. For instance, in below figure I have generated the strong name in

“mykey.snk” and assigned the same to the DLL.

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Figure 1.13 : – Strong naming your DLL

Finally we need to install the same in GAC using “gacutil” tool. Below is the figure which shows

the same. This installs one version of “ClassLibraryVersion.dll” in GAC.

Figure 1.14 : – Install the same in GAC

Now it is time to create a second version of the DLL. So here is what we will do first we will just

return a different string value for this new version DLL. You can see in the below figure I have

changed the string to return “This is New Version”. Secondly we also need to change the

AssemblyVersion to “1.1.*” in the “AssemblyInfo.cs” file. After that again compile the DLL and

run the “gacutil” to register this second version of the “ClasLibraryVersion.dll”.

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Figure 1.15 : – Rename to Assembly Version 1.1

Now when we view the GAC we can see two version of “ClassLibraryVersion” i.e. “1.1.1832.2619”

and “1.0.1832.2172” (see figure below).

Figure 1.16 : – Two version of “ClassLibraryVersion” dll.

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Now that we have created the environment of two version of the same DLL in GAC its time to

look at how client can make a choice between those versions. We need to generate “publicKeyToken”

in order to move ahead. Below is a sample print screen which shows how we can use “sn.exe” to

generated the public key token. Note the “-T” parameter.

Figure 1.17 : – Get the PublicKeyToken

Now let’s look at the client which will consume this DLL. I have just added windows form and

a button to the same. In the button click we will try to call the version function and display the

data. So below is the code in the first step we create the object of “ClassLibraryVersion.Class1”

and in the second step we call the “Version” function to display the data.

Figure 1.18 : – Client code calling the GAC class.

Now comes the most important part of the whole thing the “app.config” file which will decide

which version should be used. So add a new “app.config” file in the project and add the

“AssemblyBinding” section as show below. So you need to specify the following things:-

Assembly name in the “name” attribute of “assemblyIdentity” section.

Specify the “publicKeyToken” value in the “assemblyIndentity” section which was generated

using “sn.exe –T ‘dllname.dll’ “.

Specify the “oldVersion” and “newVersion” values in the “bindingRedirect” element. So

what ever version we want the client to use should be specified in the “newVersion” attribute.

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You can see from the figure below I have specified that client should use “1.0.*” version. So

the client will display “This is old Version”.

Figure 1.19 : – App.config file using the BindingRedirect

If you run the source code with changing version numbers you can see the below two message

boxes on different version numbers. That is “This is old version” will be displayed when

“newVersion” value is “1.0.1832.5411” and “This is new Version” will be displayed when

“newVersion” value is “1.1.1832.5427”.

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Figure 1.20 : – Different Display depending on version numbers

Note: – Source code is provided in “versioning” folder. But as you compile the DLL’s

different publicToken numbers are created so you need to run the sn.exe in your machine and

change the token number accordingly in the “App.config” file.

(A)What is CodeDom?

“CodeDom” is an object model which represents actually a source code. It is designed to be

language independent – once you create a “CodeDom” hierarchy for a program we can then

generate the source code in any .NET compliant language. So let’s try to do something real

practical and simple to just get a feel of how powerful “CodeDom” is.

Note :- You can get the source code in CD in “CodeDom” folder.

We will try to generate the following code below. The below code which will be generated does

not do anything special buy just displays a hello message and waits for the key to be pressed.

namespace InterviewQuestions

{

using System;

public class EntryPoint

{

public static void Main()

{

System.Console.WriteLine(“Hello from Interview Question series”);

System.Console.ReadLine();

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}

}

}

The “Codedom” folder in the CD has one “GenerateCode” method which returns

“CodeCompileUnit” object. “CodeDom” is nothing but a full DOM model where every object

in the structure represents a code unit. I have put comments the code so that the code is self

understandable. I have commented the code below so that readers can follow what is exactly

happening. When you click the button it generates the “MyCode.cs” and also compiles the

“Mycode.exe” in the “bin” folder.

private CodeCompileUnit GenerateCode()

{

// Definition of the Main method which will be entry point

CodeEntryPointMethod objMainMethod = new CodeEntryPointMethod();

objMainMethod.Name = “Main”;

// generate this expression: Console

CodeTypeReferenceExpression consoleType = new CodeTypeReferenceExpression();

consoleType.Type = new CodeTypeReference(typeof(Console));

// Set up the argument list to pass to Console.WriteLine()

CodeExpression[] writeLineArgs = new CodeExpression[1];

CodePrimitiveExpression arg0 = new CodePrimitiveExpression(“Hello from Interview

Question series”);

writeLineArgs[0] = arg0;

// generate this statement: Console.WriteLine(message)

CodeMethodReferenceExpression writeLineRef = new

CodeMethodReferenceExpression(consoleType, “WriteLine”);

126

CodeMethodInvokeExpression writeLine = new

CodeMethodInvokeExpression(writeLineRef, writeLineArgs);

// generate this statement: Console.ReadLine()

CodeMethodReferenceExpression readLineRef = new

CodeMethodReferenceExpression(consoleType, “ReadLine”);

CodeMethodInvokeExpression readLine = new

CodeMethodInvokeExpression(readLineRef);

// Add Main() method to a class

CodeTypeDeclaration theClass = new CodeTypeDeclaration();

theClass.Members.Add(objMainMethod);

theClass.Name = “EntryPoint”;

// Add both the code of WriteLine and Readline

objMainMethod.Statements.Add(writeLine);

objMainMethod.Statements.Add(readLine);

// Add namespace and add class

CodeNamespace ns = new CodeNamespace(“InterviewQuestions”);

ns.Imports.Add(new CodeNamespaceImport(“System”));

ns.Types.Add(theClass);

// Generate the Compile Unit

CodeCompileUnit unit = new CodeCompileUnit();

unit.Namespaces.Add(ns);

127

Sample provided is very basic but in actual project using codedom can be very complicated.

Projects where you need auto code generation codedom can be a right choice. Beware of high

bulky architecture created due to codedom.

128

(I) How can we use COM Components in .NET?

Twist : What is RCW ?

.NET components communicate with COM using RCW (Runtime Callable Wrapper). Following

are the ways with which you can generate RCW :-

Adding reference in Visual Studio.net. See figure below (Adding reference using VS.NET

2005). Wrapper class is generated and placed in the “BIN” directory.

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