Question

I have an application written in .NET 4.0 that i compile into a DLL file. I want to be able to use this DLL file in a Windows Forms .NET 2.0 application. I don’t need the application to really interact much, except just passing a couple string values to the 4.0 DLL. The DLL is pretty much a bunch of Windows which i converted to UserControls and i just need to be able to reference them to display the UserControls from the 2.0 application without having to use a different exe and having to package them separately. What is the best way to do this? Because when i try to add the reference to the DLL to the 2.0 application, it gives me and error saying the DLL is built in a newer version of .NET so i can’t do it that way. Is this where a COM object would come in? Any information and links i would really appreciate, thanks.

Answer 1

If the application can really and truly be called from a 2.0 application then the best approach is to compile it as a 2.0 application. Visual Studio 2010 (and 2008) support the notion of multi-targetted solutions. That is you can use it to compile a project for various versions of the CLR.

I would take the approach of compiling my application twice

• Once for 4.0
• Once for 2.0

This way you can use the DLL directly in your 2.0 application. No messy COM tricks needed