How to create a secondary window running in a new UI thread using WinUI Desktop App - C++/WinRT?

[alfred-png]

Hi all, I'm referring to this article https://learn.microsoft.com/en-us/windows/apps/design/layout/application-view and cannot find a way to create a second window running in its own thread. I know this feature is still experimental, but how to try it out?

Thank you in advance!

Kind regards
Alfred

[DarranRowe]

To put it bluntly, the method described is completely unavailable in a desktop application. The documentation titled Windows Runtime APIs not supported in desktop apps outright states that ApplicationView, CoreApplicationView, CoreWindow and CoreDispatcher are not supported in desktop applications. The documentation for CoreApplication states that only the Properties property is available in desktop applications.
As for being able to do it using the Windows App SDK, honestly I don't know. A lot is hidden behind Application.Start, and while theoretically the minimum you would need is a message pump and a dispatcher queue active on the thread, this is something that the Windows App SDK/WinUI 3 doesn't support and your best course of action would be to put in a feature request.

[legistek]

I haven't tried this but it appears to do the trick -

https://gist.github.com/smourier/d1961e2a8d18e762746cebe5948d36db

Update: Confirmed this works, but you do need to include

SynchronizationContext.SetSynchronizationContext(new DispatcherQueueSynchronizationContext(dq.DispatcherQueue));

to ensure awaits return on the correct UI thread.