C# class library export as COM, errors during MIDL compilation.

Question

I'm trying to create a COM library from a C# library I have. In order to do this I've defined my C# class as follows:

[Guid("830D0BFA-8045-455B-AAB7-2A7D4A16455C")]    
[ComVisible(true)]
public interface IMyInterface
{
        uint Start();
}

[Guid("22B91F20-1CC3-4276-BB51-0AE75D7DA5BB")]
[ClassInterface(ClassInterfaceType.None)]
[ComVisible(true)]
public class MyInterface_Impl : IMyInterface, IDisposable
{        
    public uint Start()
    {
        return 0;
    }
}

Additionally, I've enabled "Register for COM interop" in the project's build properties. The next step to allow a Win32 app (actually an MFC app) to use it is I think to generate a .tlb for the assembly. I'm doing this with the following post-build command:

"$(FrameworkSdkDir)\bin\NETFX 4.8 Tools lbexp.exe" "$(TargetFileName)" "$(TargetName).tlb" /win32

I see the .tlb in the build folder and then proceed to add it to the MFC project, right clicking it and setting it to Item Type: MIDL tool. When I then build this project, I get the following warnings and errors:

1>------ Build started: Project: My_Dll_Test_MFC, Configuration: Debug Win32 ------
1>Processing ..\My_Dll\bin\x86\Debug\My_Dll.tlb
1>My_Dll.tlb
1>..\My_Dll\bin\x86\Debug\My_Dll.tlb(1): warning C4335: Mac file format detected: please convert the source file to either DOS or UNIX format
1>..\My_Dll\bin\x86\Debug\My_Dll.tlb(1): error MIDL2025: syntax error : expecting an interface name or DispatchInterfaceName or CoclassName or ModuleName or LibraryName or ContractName or a type specification near "MSFT"
1>..\My_Dll\bin\x86\Debug\My_Dll.tlb(1): error MIDL2026: cannot recover from earlier syntax errors; aborting compilation
1>Done building project "My_Dll_Test_MFC.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

What mistake have I made here?

Accepted Answer

Going to answer my own question here. The mistake is you don't do that with the tlb, only the idl. The way to import it is with the #import directive, which seems to build just fine.

C# class library export as COM, errors during MIDL compilation.

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