Why is a "bindingRedirect" added to the app.config file after adding the Microsoft.Bcl.Async package?

c# .net app-config base-class-library
GameScripting picture GameScripting · Jun 4, 2013 · Viewed 25.2k times · Source

I was wondering why nuget added the following code to my applications app.config file, after installing the Microsoft.Bcl.Async:

<runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
            <assemblyIdentity name="System.Runtime" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-2.5.19.0" newVersion="2.5.19.0" />
        </dependentAssembly>
        <dependentAssembly>
            <assemblyIdentity name="System.Threading.Tasks" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" />
            <bindingRedirect oldVersion="0.0.0.0-2.5.19.0" newVersion="2.5.19.0" />
        </dependentAssembly>
    </assemblyBinding>
</runtime>

If I remove this XML-element from the config, the app will not work properly.

As far as I understand it, we can use the bindingRedirect to make the app load a newer or older version of an assembly in case the version we were using when compiling the EXE is gone.
However I am using exactly the version 2.5.19.0, why would I need a redirect then?

the version of my dll

Why do I need this bindingRedirect?

Answer

Richard Deeming picture Richard Deeming · Jun 4, 2013

The assemblies Microsoft.Threading.Tasks and Microsoft.Threading.Tasks.Extensions are still referencing v1.5.11.0 of System.Runtime and System.Threading.Tasks.

Without the bindingRedirect, the Microsoft.* assemblies would try to load an old version of the System.* assemblies, which would fail.

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