[WinUI 3] COMException: The application called an interface that was marshalled for a different thread.

[Diyari-Kurdi]

Hello,
I'm facing an issue using SignalR in WinUI 3. When SignalR fires an event and if I change a property inside that event while the property is bound to the View, it throws this exception:
System.Runtime.InteropServices.COMException: 'The application called an interface that was marshalled for a different thread. (0x8001010E (RPC_E_WRONG_THREAD))'

Source Code:
WinUI_SignalR_Demo.zip

[kmgallahan]

The result of the GetMessage() is coming back on a non-UI thread, meaning PropertyChanged is invoked on a non-UI thread.

GPT-4 can handle the rest:

---

In WinUI or UWP, you cannot invoke PropertyChanged on a non-UI thread because the UI elements can only be accessed from the UI thread. If you attempt to access UI elements from a non-UI thread, you may encounter unexpected behavior or crashes in your application.

To update UI elements from a non-UI thread, you can use the Dispatcher.RunAsync method in UWP or DispatcherQueue.TryEnqueue method in WinUI 3. Here's an example of how to use Dispatcher.RunAsync in UWP:

Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,
() =>
{
    // update your UI here
    Update(i);
});

Source 2

For WinUI 3, you can use the DispatcherQueue.TryEnqueue method:

this.DispatcherQueue.TryEnqueue(() => 
{
    // update your UI here
    Update(i);
});

Source 4

It's worth noting that in WinUI 3, the CoreDispatcher has been succeeded by DispatcherQueue. Most UI objects in WinUI 3 now have a DispatcherQueue property instead of a CoreDispatcher property. You can access the DispatcherQueue from any UI element or Window Source 4.

In summary, when updating UI elements from a non-UI thread, you should use Dispatcher.RunAsync in UWP or DispatcherQueue.TryEnqueue in WinUI 3 to ensure the changes are made on the UI thread to avoid any issues or crashes.