Thottam R. Sriram

Introduction to Versioning and BindingRedirect

I want to share with you this sample that demonstrates how to version an assembly. An

AssemblyIdentity consists of five parts:

 

1. AssemblyName
2. Public key
3. Version
4. Culture
5. Processor Architecture

 

How do you specify all of these in an assembly? It is real simple. Let us walk over step by step to understand this with a simple example.

 

Let us create an assembly and version it as 1.0.0.0.

 

Let us create a directory C:\versionsample\bin\v1\helper.cs as below

 

using System;

using System.Reflection;

[assembly: System.Reflection.AssemblyVersion("1.0.0.0")]

public class Foo

{

    public void Bar()

    {

        Console.WriteLine("Inside HelperMethod: Version = {0}", (Assembly.GetExecutingAssembly()).ToString());

    }

}

 

Now let us sign it with a key pair. In order to do that run sn –k sgkey.snk and generate key pair.

 

You can compile the assembly as below

 

csc /target:library /out:helper.dll /keyfile:sgkey.snk helper.cs

 

If you ildasm helper.dll you will see the version number to be 1.0.0.0 and the public key as specified in the snk file.

 

Let us create a 2.0.0.0 version of the assembly we has before:

 

Let us create a directory C:\versionsample\bin\v2\helper.cs as below

 

using System;

using System.Reflection;

[assembly: System.Reflection.AssemblyVersion("2.0.0.0")]

public class Helper

{

    public void HelperMethod()

    {

        Console.WriteLine("Inside HelperMethod: Version = {0}", (Assembly.GetExecutingAssembly()).ToString());

    }

}

 

You can compile this with the same key file to a library

csc /target:library /out:helper.dll /keyfile.sgkey.snk helper.cs

 

Let us write the application as below and compile it with helper.dll from the v1 directory as below:

 

using System;

public class sample

{

    static void Main(string[] args)

    {

        Foo f = new Foo();

        f.Bar();

    }

}

 

csc /reference:bin\v1\helper.dll Application.cs

 

Let us create a config file for the application as below:

Application.exe.config:

<configuration>

   <runtime>

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

         <dependentAssembly>

            <assemblyIdentity name="Helper"

                              publicKeyToken="bcabfaff346163aa"

                              culture="neutral" />

            <codeBase version="1.0.0.0"

                      href="c:\versionsample\bin\v1\helper.dll"/>

            <codeBase version="2.0.0.0"

                      href="c:\versionsample\bin\v2\helper.dll"/>

         </dependentAssembly>

      </assemblyBinding>

   </runtime>

</configuration>

 

If you run the application, you will get the following output:

Inside HelperMethod: Version = helper, Version=1.0.0.0, Culture=neutral, PublicK

eyToken=bcabfaff346163aa

 

In order to bind the application to version 2.0.0.0 of the helper assembly, let us add a bindingRedirect which moves version 1.0.0.0 to 2.0.0.0.

 

<configuration>

   <runtime>

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

         <dependentAssembly>

            <assemblyIdentity name="Helper"

                              publicKeyToken="bcabfaff346163aa"

                              culture="neutral" />

            <bindingRedirect oldVersion="1.0.0.0" newVersion="2.0.0.0"/>

            <codeBase version="1.0.0.0"

                      href="c:\versionsample\bin\v1\helper.dll"/>

            <codeBase version="2.0.0.0"

                      href="c:\versionsample\bin\v2\helper.dll"/>

 

         </dependentAssembly>

      </assemblyBinding>

   </runtime>

</configuration>

 

Now if you run the application you will see the following output:

Inside HelperMethod: Version = helper, Version=2.0.0.0, Culture=neutral, PublicK

eyToken=bcabfaff346163aa