Integration Issues: C++/WinRT Runtime Component & C# WinUI 3 Project on .NET 9 – WinMD and C++/CLI Interop Problems

[KrishBaidya]

Description:

I'm encountering significant challenges when integrating a C++/WinRT Runtime Component into my C# WinUI 3 project, which is targeting .NET 9. It appears that .NET 9 does not support referencing Windows Metadata (.winmd) files directly, leading to errors during compilation. Additionally, using a C++/CLI wrapper to bridge the gap is problematic due to incompatibilities between C++/WinRT and /clr modes. I've attached a screenshot of the error message ("The method or operation is not implemented") encountered when creating a new C++/WinRT Runtime Component project.

Steps to Reproduce:

1. Create a new C++/WinRT Runtime Component project using the WinUI 3 template in Visual Studio.
2. Attempt to reference the generated .winmd file from a C# WinUI 3 project targeting .NET 9.
3. Encounter the error:

MyNewProject.winmd cannot be referenced. Referencing a Windows Metadata component directly when targeting .NET 5 or higher is not supported. For more information, see https://aka.ms/netsdk1130

4. Remove App.xaml/App.xaml.cpp from the C++/WinRT project and try referencing it, but the issue persists.
5. Attempt to create a C++/CLI wrapper to bridge to the C++/WinRT code, but this fails due to the incompatibility of C++/WinRT code with the /clr environment required by C++/CLI.
6. When creating a new C++/WinRT Runtime Component project, a separate error appears ("The method or operation is not implemented"). See attached screenshot.

Expected Behavior:

• A clear integration path where the C++/WinRT Runtime Component can be consumed by a C# WinUI 3 project targeting .NET 9 without running into the WinMD reference limitation.

Steps I've Already Tried:

• Verified that all required Visual Studio workloads and components are installed and up to date.
• Attempted using multiple project templates (both Runtime Component and Blank App templates).
• Explored creating a C++/CLI wrapper, which ultimately failed due to the incompatibility between /clr and C++/WinRT code.

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Any assistance or insights into a viable integration strategy would be greatly appreciated. Thank you for your work on WinUI 3 and the Windows App SDK!

[DarranRowe]

Have you tried not going down the C++/CLI route but instead use C#/WinRT (CsWinRT) to create a projection?

The error message referencing the .winmd file states that .NET 5 and higher cannot reference .winmd files directly. This was done deliberately. C#/WinRT was created to allow C# projects the access WinRT components. C#/WinRT works in a similar way to C++/WinRT here.

[KrishBaidya]

Have you tried not going down the C++/CLI route but instead use C#/WinRT (CsWinRT) to create a projection?

The error message referencing the .winmd file states that .NET 5 and higher cannot reference .winmd files directly. This was done deliberately. C#/WinRT was created to allow C# projects the access WinRT components. C#/WinRT works in a similar way to C++/WinRT here.

Are you telling me that I should use Microsoft.Windows.CsWinRT package on my C++/WinRT Runtime Component Project as well as on my C# project? I have already tried that but maybe either I could not understand what I should do next, or it just didn't work!

[DarranRowe]

Are you telling me that I should use Microsoft.Windows.CsWinRT package on my C++/WinRT Runtime Component Project as well as on my C# project? I have already tried that but maybe either I could not understand what I should do next, or it just didn't work!

That isn't what I'm telling you at all.

You should create a C# class library project that goes between the C++ component and the C# application. This C# class library is what uses C#/WinRT to create the projection.

A sample that I wrote can be found here.

[KrishBaidya]

Okay, the issue has been resolved by -

1. Installing Microsoft.Windows.CsWinRT package to my C# Project.
2. Adding <CsWinRTIncludes>MyNewC++Project</CsWinRTIncludes> in my C# project.
3. Referening my C++ Project on my C# Project.

It didn't require creating a C# Class Library. Still, thanks for your help.

I am closing this issue now...