Registration-free Interop between a 64-bit COM dll and a C#/.Net application

Question

I am trying to get registration-free COM interop between a 64-bit COM dll and a C# app to work.

In the answers to a previous question of mine, I got help that allowed me to successfully call a HelloWorld method on the 64-bit COM dll for C#.

However, this was only possible by registering the COM dll globally using regsrv32.exe.

Based on this answer to a related question, I think that I need to set the Isolated flag on the reference of the COM dll to true. However, this leads to the following build error:

Problem isolating COM reference 'ComLibInteropLib': 
    No registered classes were detected for this component.

The answer to a question on MSDN social seems to indicate that there is a solution for this problem if one can compile a 32-bit version of the dll.

However, my COM interop library needs to link to a 'normal' C++ dll, for which I do not have the source and that is only available as x64.

So my question is: How can I enable the Isolated flag (or otherwise get side-by-side to work) between a 64-bit COM dll and a C# application?

I am happy to use regsrv32.exe on my machine or other developer's machine, but we cannot register any COM dlls on production machines, where the final application must run.

Answer 1

This is a side-effect of the original problem you had, the COM server wasn't getting registered properly. When you Isolated option to true, the build system auto-generates the required manifest entries for you. But the content of the manifest needs to come from somewhere, it uses the registry keys. Since they are not there, it can't generate the manifest.

You can write the manifest yourself but that requires enough insight in what the manifest should look like. With very high odds of making mistakes, the incantations are quite obscure. So avoid that, you just need to get the COM server registered to get ahead. Just on your build machine, it doesn't have to be registered on the client's machine since it will use the manifest.

You mentioned a 64-bit COM server, that's another possible failure mode. The build system is still 32-bit so you'll have high odds that it looks at the wrong keys. HKLM\Software\Wow6432Node instead of HKLM\Software. Battle that problem by building both flavors of the COM server. Beware of having the same kind of problem when you use Regsvr32.exe yourself, there are two of them. The one in c:\windows\syswow64 should be used to register the 32-bit version of the server, the one in c:\windows\system32 for the 64-bit version.