Porting UWP to .NET9 with C++ projects.

[MartinRichards23]

I'm in the process of updating our UWP app to new .NET9 AOT. The front end of our app is C#, but the engine is a "Universal Windows" C++ project.

I'm unclear how those C++ projects need to be updated so we can continue to reference them from the C# projects in the new .NET9 AOT world?

I'm hoping project config just needs to be updated in some way, but I can't find any documentation on this process.

[dongle-the-gadget]

There's no need to change anything on the C++ side, other than enabling the "Desktop compatible" setting in Properties.

[MartinRichards23]

Thanks for your quick reply!

I've set the "Desktop compatible" setting in Properties, but when I compile I get the error:

the_cpp_project.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

[dongle-the-gadget]

Are you registering the classes correctly? The samples are unpackaged so you need to make sure that app.manifest is included as Application Manifest and that the file declares those classes under activatableClasses.

[manodasanW]

.NET 8 and later have a change where they no longer use the win10-x64 runtime identifier and instead use win-x64. That might need to be reflected in the nuspec used by that sample if you are trying it with .NET 9.

[MartinRichards23]

I've just tried replacing win10-x64 with win-x64 in the nuspec in the sample project, doing a clean build, but still encountering the same "Class not registered" issue though.

[joellyons]

@MartinRichards23 were you able to figure out the "class not registered" exception?

[MartinRichards23]

No, I'm hoping this is going to be fixed in the upcoming 2.3 release.

[MartinRichards23]

I have opened issue #1952 to update the samples, as this is important for our application.

[joellyons]

I'm having a similar problem. I have a C++ WinRT library we've been calling from a UWP app for years and are attempting to update the app to .NET 9. The app is mostly running in .NET 9 now, but we've had no luck calling into the C++ library. I've set the "Windows Desktop Compatible" property in the C++ library to Yes. I've created a projection project, nuget packaged it (see below), and reference that from the app. The app compiles and runs, but as soon as I try to create an instance of a type from the C++ library, I get a "Class not registered" error.

[joellyons]

If I try a "private projection" instead, within the app itself...

I get:
FileNotFoundException
HResult=0x8007007E Message=The specified module could not be found. (0x8007007E)
Source=System.Private.CoreLib
StackTrace: at System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(Int32 errorCode)
at WinRT.ActivationFactory.Get(String typeName, Guid iid)
at HoloSound.Sound.get__objRef_global__HoloSound___ISoundFactory()

But the HoloSound.dll is in the output folder.

[joellyons]

I should mention, the C++ WinRT library is referenced by an intermediate library, which is then used by the exe. The intermediate library and the exe were both old UWP projects and are being converted to .NET 9 UWP. Not sure if I need to do anything extra in that case. The private projection I attempted above was in the intermediate library because the exe doesn't call the C++ library directly.

[joellyons]

Sorry, I forgot to post an update... I was finally able to get a "private projection" working. After lots of struggling, I cleaned the output folders and started over, following instructions carefully, and it worked! My only guess is that I was somehow referencing an older version of my C++ WinRT project that didn't have the "Windows Desktop Compatible" property set to Yes.