easiest way to convert .NET project from 4.5 to 4.0?

Question

I have a .NET application that I built in 4.5, which has references to a bunch of libraries that were built in 4.5, which themselves have references to 4.5, etc. A user group that I'm trying to distribute the application to is having problems running the executable because they have 4.0 installed; in particular, they're getting a MissingMethodException:

Method not found: 'System.Type System.Runtime.InteropServices.Marshal.GetTypeFromCLSID(System.Guid)'.

Because we may have trouble getting each user upgraded to 4.5 (as none of them have admin permissions on their machines and this would require a separate upgrade request for each user), I'm looking at finding an easy way to rebuild the project as 4.0. This seems to require that I rebuild every library and its referenced libraries in 4.0; is there an easier way to do this than going through each library one by one and building a 4.0 version? I'm thinking maybe like a one-click option for "Rebuild all referenced libraries in target framework" or something like that.

Answer 1

If you have dependencies on .Net 4.5 DLLs then you will need to also get .Net 4.0 versions of those if you want to successfully downgrade your project. A .Net project can only reference .Net DLLs up to the same version of .Net as the referencing assembly.

The easiest way to do this is to use something like NuGet to manage your dependencies. Note that when you change the target framework version of your project in VS you will need to uninstall and re-install dependencies with NuGet as NuGet does not automatically do this for you when you change the target framework version.

Of course if all the dependencies are to your own code and you aren't publishing this through a dependency management system like NuGet you will need to downgrade all your other code to .Net 4.0 as well

Answer 2

When I use Visual Studio, I right click on the project, change the framework, fix the References and recompile. Usually straight forward.