Question

I’m trying to load a mixed managed application compiled and targeted for Framework 3.5 in the 4.0 CLR.

We have a .config file next to the .exe where I’ve added this node:

<?xml version="1.0"?> 
<configuration>
<startup>
    <supportedRuntime version="v4.0.21006" />
</startup>

Unfortunately, the app crashes out on startup with a nasty callstack. Can someone in the know confirm that a mixed managed app (.exe is C++/CLI) will not load in 4.0 if it was compiled for 3.5?

I’m watching a Channel9 video about side-by-side CLR hosting, and one of the devs seems to imply that this is the case:

http://channel9.msdn.com/shows/Going+Deep/CLR-4-Side-by-Side-In-Process-What-How-Why/

Thanks!

Answer 1

You need to set useLegacyV2RuntimeActivationPolicy if you want to load a CLR 2 (.NET 3.5) mixed mode assembly in a CLR 4 process:

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

Without this, you’ll get a nasty exception.