Force visual studio to see that I have changed the IDL for a COM interface

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I have an in-process COM Service written in C++. The COM interface is defined by an IDL file.
I have a C# application that uses that COM interface.
I modify the IDL of the C++ COM Service, re-compile and re-register it.
But the interface change is not being seen when I re-compile the C# application.
Visual Studio seems to be caching the original interface definition somewhere and not updating it. Even if I remove the COM reference from the C# project and re-add it I still see the old interface.

Does anyone know how to force an update of the COM interface so I can compile the C# app with the revised interface?

This is with Visual Studio 2015.

What I have tried:

Various combinations of cleaning and re-compiling everything.

Posted 12-May-21 9:07am

Keith Barrett

Updated 12-May-21 22:28pm

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Shao Voon Wong 12-May-21 23:35pm

Did you unregister the old COM object before registering the new one? You can remove the old COM reference from the C# project and add new one again and recompile.

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Keith Barrett · Answer 1 · 2021-05-12T22:28:00

Solution 1

I've found a solution to this. The steps are
1. Recompile the C++ Service.
2. Locate the TLB file for the service. It will be in the same place as the OBJ files for the project.
3. Use TLBIMP to generate a .Net DLL for the service.
4. Register the DLL using REGASM.
5. Re-open the C# project and re-build. It will now get the updated interface definition.

Posted 12-May-21 22:28pm

Keith Barrett

Comments

Shao Voon Wong 14-May-21 2:13am

I suggest you put these steps in the post-build event of the C++ COM project so that your C# project always gets the latest COM object.