Bug: SynchronizationContext is not set for secondary views in a UWP app

[benstevens48]

Description

SynchronizationContext.Current is null for any secondary application views (created by CoreApplication.CreateNewView()) in a UWP app using CsWinRT. This means after awaiting most async methods from the UI thread of a secondary view, trying to set a control property crashes due to being on the wrong thread. It seems the workaround is to use the Windows.System.DispatcherQueueSynchronizationContext type provided by CsWinRT as follows when setting up the view. However, I couldn't find this documented anywhere.

 await newView.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
 {
     var context = new DispatcherQueueSynchronizationContext(DispatcherQueue.GetForCurrentThread());
     SynchronizationContext.SetSynchronizationContext(context);
     //...

Is this a bug or is it a necessary workaround that needs documenting? This just worked by default with the old .Net Native toolchain.

PS the SynchronizationContext for the main thread is correctly set to Windows.System.DispatcherQueueSynchronizationContext in the generated main function.

Steps To Reproduce

See description

Expected Behavior

No crash

Version Info

CsWinRT 2.2, Windows 25H2, UWP.

Additional Context

No response

[benstevens48]

Also, in the above, make sure the RunAsync callback is not async, else the SynchronizationContext will be unset when the method completes. (Just spent an hour working that out...)

[dongle-the-gadget]

.NET 9+ doesn’t allow thread creation hooking like .NET Native so this will be required.

[manodasanW]

This sounds like something that just needs to be documented.