(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]
[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
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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
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
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”.
culture="neutral"/>
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”);
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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);
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