What 'additional configuration' is necessa

Question

I have a project in which I'd like to use some of the .NET 4.0 features but a core requirement is that I can use the System.Data.SQLite framework which is compiled against 2.X. I see mention of this being possible such as the accepted answer here but I don't see how to actually achieve this.

When I just try and run my 4.0 project while referencing the 2.X assembly I get:

Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.

What "additional configuration" is necessary?

Answer 1

Using 2.0 and 4.0 assemblies together isn't quite straight forward.

The ORDER of the supported framework declarations in app.config actually have an effect on the exception of mixed mode being thrown. If you flip the declaration order you will get mixed mode error. This is the purpose of this answer.

So if you get the error in a Windows Forms app, , try this, mostly Windows Forms apps.

  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client"/>
    <supportedRuntime version="v2.0.50727"></supportedRuntime>
  </startup>

Or if the project is not Windows Form. In a Web project add this to web.config file.

  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
    <supportedRuntime version="v2.0.50727"></supportedRuntime>
  </startup>

Answer 2

In order to use a CLR 2.0 mixed mode assembly, you need to modify your App.Config file to include:

<?xml version="1.0"?>
<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
</configuration>

The key is the useLegacyV2RuntimeActivationPolicy flag. This causes the CLR to use the latest version (4.0) to load your mixed mode assembly. Without this, it will not work.

Note that this only matters for mixed mode (C++/CLI) assemblies. You can load all managed CLR 2 assemblies without specifying this in app.config.

Answer 3

This forum post on the .NET Framework Developer Center. It might provide some insight.

(Add to the app's config file.)

<configuration>
  <startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0"/>
  </startup>
</configuration>

Answer 4

If your are working in a web service and the v2.0 assembly is a dependency that has been loaded by WcfSvcHost.exe then you must include

<startup useLegacyV2RuntimeActivationPolicy="true">
    <supportedRuntime version="v4.0" />
</startup>

in ..\Microsoft Visual Studio 10.0\Common7\IDE\ WcfSvcHost.exe.config file

This way, Visual Studio will be able to send the right information through the loader at runtime.