Can't work in WinUI 3 project

[huoyaoyuan]

Start from WinUI 3 Preview 3 template project

Add package reference to Microsoft.Windows.CsWin32, with GetActiveWindow in NativeMethods.txt
Make a call to the method anywhere.

The IDE can correctly analysis all the occurrence and references of the method. However, when building the project, the command line output shows error CS0234: No member 'Windows' in namespace 'Microsoft'.

I think this is dotnet/roslyn#46420 , in another way.

[AArnott]

I am not familiar with WinUI 3. But the symptoms are very similar to #7. Can you try the workaround documented there to see if it helps? Otherwise, we may need to move your bug to the WinUI team.

[huoyaoyuan]

No, the workaround for #7 doesn't work here.

Seems that WinUI invokes legacy roslyn somehow.

[AArnott]

@huoyaoyuan Where can I get this WinUI project template you're talking about so I can test it? Any idea where we can file issues against it?

[huoyaoyuan]

@AArnott

https://github.com/microsoft/microsoft-ui-xaml
https://aka.ms/winui3/preview3-download

I can open issue myself there. They have been incompatible with several compiling stuff like dotnet build, <Nullable>enable</Nullable>.

If you have internal contacts, you may ask them about their interaction with roslyn and msbuild team. Thanks.

[dotMorten]

I'm successfully using this with WinUI3. I've used this to have my WinUI3 app generate a tray icon, and clicking the tray icon will bring the WinUI3 window to the top.
Are you targeting Win32 or UWP?

[huoyaoyuan]

I'm targeting Win32.

[dotMorten]

OK this is odd. Just created a new project and hit the same thing while compiling:

[dotMorten]

Investigating some more: The reason it worked for me was I was building a class library. But the moment I add XAML to that class library, this error occurs.

[huoyaoyuan]

Yes. The #nullable issue occurs too when I add XAML. So I suspect they have the same root cause.

[dotMorten]

Seems like the XamlPrecompile step isn't including the generated files, and thus fails:

[huoyaoyuan]

OK. So if XamlPrecompile invokes csc with custom command line and may not respect csproj, it's reasonable to report warning for no <Nullable>enable</Nullable>.

[dotMorten]

Seems duplicate to this: dotnet/roslyn#46300

[Sergio0694]

Not sure if this has already been mentioned, but it seems this is not specific to WinUI 3 - I get the same exact error when trying to use a source generator that interacts with a XAML-related file in any way on vanilla UWP (SDK 19041) as well 🤔

[dotMorten]

@Sergio0694 Yes agreed. Not specific to this. It should probably be moved to the WinUI repo

[AArnott]

Some investigations led to dotnet/msbuild#6096, which may fix the WinUI problem.

[dotMorten]

@AArnott That helps some.
As mentioned in email "offline", the code generator need to prefix usings with global:: or it'll clash with WinUI. (props to @chsienki for discovering this)

[dotMorten]

Just confirming that 0.1.370-beta works great with WinUI 3. Thank you!