What's the best way to target multiple versions of the .NET framework?

Question

I'm building a class library and I will deploy it a NuGet package, which lets me choose different assemblies to be added as references based on the .NET framework version of the project it's added to. This is a very nice feature, but what I'm wondering is whether it is possible to have a single class library project, and build it against mulitple versions of the .NET framework?

I'd rather avoid having:

MyLibrary40.dll and MyLibrary45.dll

if possible, because the two projects would have to share a lot of code. The 4.5 version will be offering async functions, which is a 4.5 feature.

Does anyone know what the best approach for this is? Can I use multiple build configurations? Or must I go down the separate project route?

If I was working in C++ I'd probably use multiple configurations and #if blocks around the functions that are only supported in one configuration, but I worry this would lead to me having two assemblies with the same name that do different things.

Thanks in advance!

Answer 1

You will at least need one VisualStudio Solution with 2 projects (one for .net 4 and one for .net 4.5).

Add all codefiles to the .net 4-project and in the other project you add the code files as link (use "Add Existing Item..."-Dialog and chose Add as link)

Now you add all codes and classes for .NET 4.5 to your 4.5-project.

Additionally you should define your own compiler switches (conditional compilation symbols) to your projects. Like NET4 for your .net 4-project and NET4.5 to your .net 4.5-project)

You set the switches in the project settings under Build->General->Conditional Compilation Switches

In your code you can use the switches as follows to generate code for .NET 4 or .NET 4.5

#if NET4   // code only for .NET 4 #endif  // code for all framework versions.  #if NET45   // code only for .NET 4.5 #endif