Can you use a .NET 4.0 dll in a 3.5 project?

Can you use a .NET 4.0开发者_如何学JAVA dll in a 3.5 project?

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Nope. You can use a .Net 3.5 assembly in a 4.0 project, but not the other way around.

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No you can't. An assembly compiled against .NET 4.0 can be loaded only by the CLR 4.0. On the other hand the CLR 4.0 can load assemblies compiled against .NET 3.5.

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https://code.msdn.microsoft.com/Using-a-NET-4-Based-DLL-bb141db3/

Use our .NET 4 DLL via COM

using System; 
using Net4ToNet2Adapter; 

namespace Net2Assembly 
{ 
    class Program 
    { 
        static void Main(string[] args) 
        { 
            Console.WriteLine("CLR version from EXE: {0}", Environment.Version); 
            Type myClassAdapterType = Type.GetTypeFromProgID("Net4ToNet2Adapter.MyClassAdapter"); 
            object myClassAdapterInstance = Activator.CreateInstance(myClassAdapterType); 
            IMyClassAdapter myClassAdapter = (IMyClassAdapter)myClassAdapterInstance; 
            myClassAdapter.DoNet4Action(); 
        } 
    } 

}