使用4.6v dll而不将当前项目目标框架从v4.0升级到v4.6 C＃

Question

I have a requirement where I should not upgrade my WPF application of 4.0 version to 4.6, because we are using some legacy third party controls which is leading to hell number of error, but I should use a dll of version 4.6 in my WPF project. Please suggest me some workaround to achieve this.

I am new to COM programming. I think the above is possible for example, we use outlook 2016 dlls, etc., which uses 4.5v in our 4.0 projects by adding them as COM components to our projects. All it needs is to runtime version of the OS should be 4.5.

Answer 1

You cannot use .Net 4.6 assemblies in a process which has been initialized with the 4.0 runtime. The reason is that the runtime for 4.6 is the same runtime for 4.0, and thus it can't run side-by-side like 2.0 assemblies can. The VM that gets loaded in process will not interpret the method table of the loaded types correctly, even if they are exported as COM interfaces. The reason is that even if is going through a layer of Runtime / COM / Runtime indirection, the same 4.0 CLR and system assemblies are loaded in that process, and the instantiation of a runtime type from 4.6 assembly appears to cause the CLR method RuntimeTypeHandle::CreateInstance to interpret the method table incorrectly.

The only way you could do this is if you hosted the 4.6 assembly in another process and remoted to it. This is likely what is happening with the Outlook add-ins anyway, they are being hosted by dllhost.exe or similar shell process out of the Outlook process.

Answer 2

You can find the screenshot here for my above comment. As long as we have 4.6 runtime in the machine. we can do it using reflection:

demo_screenshot