Bug: `CompositorController.CommitNeeded +=` is broken in .Net Framework

[Shan-Zhou]

Description

The event CompositorController.CommitNeeded is unusable when using embedded C#/WinRT + .Net Framework 4.7.2. An exception System.InvalidCastException: 'Specified cast is not valid.' is thrown.

Steps To Reproduce

1. Create an empty WPF project, then modify the csproj to embed C#/WinRT (CsWinRTWindowsMetadata can be local because I just copied them from my local machine...; the include/exclude is a combination I found that can make Windows.UI.Composition work without embedding unnecessary components)

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
	<LangVersion>latest</LangVersion>
	<TargetFrameworks>net472;net8.0-windows</TargetFrameworks>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.2.0" />
		<PackageReference Include="System.Memory" Version="4.6.3" />
	</ItemGroup>

	<PropertyGroup>
		<NoWarn>$(NoWarn);CS8305</NoWarn>
		<CsWinRTMessageImportance>high</CsWinRTMessageImportance>
		<CsWinRTEmbedded>true</CsWinRTEmbedded>
		<CsWinRTWindowsMetadata>
			WinMetadata\Windows.Data.winmd
			WinMetadata\Windows.Devices.winmd
			WinMetadata\Windows.Foundation.winmd
			WinMetadata\Windows.Globalization.winmd
			WinMetadata\Windows.Graphics.winmd
			WinMetadata\Windows.Storage.winmd
			WinMetadata\Windows.System.winmd
			WinMetadata\Windows.UI.winmd
		</CsWinRTWindowsMetadata>
		<CsWinRTIncludes>
			Windows.Data.Text.TextSegment;
			Windows.Devices.Geolocation;
			Windows.Devices.Input;
			Windows.Foundation;
			Windows.Globalization.DayOfWeek;
			Windows.Graphics.DirectX;
			Windows.Graphics.Effects;
			Windows.Graphics.IGeometrySource2D;
			Windows.Graphics.PointInt32;
			Windows.Graphics.RectInt32;
			Windows.Graphics.SizeInt32;
			Windows.Storage;
			Windows.System.DispatcherQueue;
			Windows.System.IDispatcherQueue;
			Windows.System.IDispatcherQueueController;
			Windows.System.IDispatcherQueueShutdownStartingEventArgs;
			Windows.System.IUser;
			Windows.System.User;
			Windows.System.VirtualKey;
			Windows.UI;
		</CsWinRTIncludes>
		<CsWinRTExcludes>
			Windows.Devices.Input.IPenDevice;
			Windows.Devices.Input.IPenDevice2;
			Windows.Devices.Input.PenDevice;
			Windows.Devices.Input.Preview;
			Windows.Foundation.Diagnostics;
			Windows.Foundation.PropertyType;
			Windows.UI.ApplicationSettings;
			Windows.UI.Composition.Scenes;
			Windows.UI.Core.Preview;
			Windows.UI.Input.Core;
			Windows.UI.Input.Inking;
			Windows.UI.Input.IRadialController;
			Windows.UI.Input.Preview;
			Windows.UI.Input.RadialController;
			Windows.UI.Input.Spatial;
			Windows.UI.Notifications;
			Windows.UI.Shell;
			Windows.UI.StartScreen;
			Windows.UI.Text.Core;
			Windows.UI.ViewManagement;
			Windows.UI.WebUI;
			Windows.UI.WindowManagement;
			Windows.UI.Xaml;
		</CsWinRTExcludes>
	</PropertyGroup>
</Project>

2. Create compositor controller and set up its CommitNeeded

var controller = DispatcherQueueController.CreateOnDedicatedThread();
controller.DispatcherQueue.TryEnqueue(() =>
{
    try
    {
        var controller = new Windows.UI.Composition.Core.CompositorController();
        controller.CommitNeeded += (s, e) => { s.Commit(); };
        var compositor = controller.Compositor;
        // ...
    }
    catch (Exception e) {  }
});

Expected Behavior

No exception (currently I can only use it when targeting .Net 8)

Version Info

Tested with both C#/WinRT 2.2 and 2.3.0-prerelease.250720.1
.Net SDK version is 10.0.100-rc.1.25451.107
OS: Windows 11 27954.1
winmd files are copied from my local machine

Additional Context

Call Stack

 	mscorlib.dll!System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(int errorCode)	Unknown
 	WpfApp1.exe!WinRT.IObjectReference.As<ABI.WinRT.Interop.IWeakReferenceSource.Vftbl>(System.Guid iid) Line 170	C#
 	WpfApp1.exe!WinRT.IObjectReference.As<ABI.WinRT.Interop.IWeakReferenceSource.Vftbl>() Line 166	C#
 	WpfApp1.exe!ABI.WinRT.Interop.IWeakReferenceSource.IWeakReferenceSource(WinRT.IObjectReference obj) Line 112	C#
 	[Native to Managed Transition]	
 	[Managed to Native Transition]	
 	WpfApp1.exe!ABI.WinRT.Interop.EventSourceCache.Create(WinRT.IObjectReference obj, int index, System.WeakReference<object> state) Line 77	C#
 	WpfApp1.exe!ABI.WinRT.Interop.EventSource<Windows.Foundation.TypedEventHandler<Windows.UI.Composition.Core.CompositorController, object>>.Subscribe(Windows.Foundation.TypedEventHandler<Windows.UI.Composition.Core.CompositorController, object> handler) Line 104	C#
 	WpfApp1.exe!ABI.Windows.UI.Composition.Core.ICompositorController.CommitNeeded.add(Windows.Foundation.TypedEventHandler<Windows.UI.Composition.Core.CompositorController, object> value) Line 438	C#
 	WpfApp1.exe!Windows.UI.Composition.Core.CompositorController.CommitNeeded.add(Windows.Foundation.TypedEventHandler<Windows.UI.Composition.Core.CompositorController, object> value) Line 103	C#
 	WpfApp1.exe!WpfApp1.MainWindow..ctor.AnonymousMethod__0_1() Line 28	C#
 	WpfApp1.exe!ABI.Windows.System.DispatcherQueueHandler.Do_Abi_Invoke.AnonymousMethod__26_0(Windows.System.DispatcherQueueHandler invoke) Line 1498	C#
 	WpfApp1.exe!WinRT.ComWrappersSupport.MarshalDelegateInvoke<Windows.System.DispatcherQueueHandler>(System.IntPtr thisPtr, System.Action<Windows.System.DispatcherQueueHandler> invoke) Line 72	C#
 	WpfApp1.exe!ABI.Windows.System.DispatcherQueueHandler.Do_Abi_Invoke(System.IntPtr thisPtr) Line 1496	C#

I tried to let the debugger go step by step and it seems that the issue is that the CompositorController cannot be casted (QueryInterface) to IWeakReferenceSource

[dongle-the-gadget]

Couldn't you use .NET Framework's built-in WinRT interop by referencing Microsoft.Windows.SDK.Contracts? I believe .NET Framework support is only provided for a limited scenario (that I don't remember and will be removed in C#/WinRT 3.0 anyways)

[Shan-Zhou]

It is possible. Currently I use CsWinRT because by embedding, I can code as if I am targeting a single framework. When using Microsoft.Windows.SDK.Contracts I have to look up https://github.com/microsoft/CsWinRT/blob/master/docs/interop.md quite frequently...

Btw is there any technical reason for deprecating .Net Framework support? Currently it seems to work well

[dongle-the-gadget]

.NET Framework does not use CsWinRT, as it has its own mechanism of WinRT interop, and CsWinRT's .NET Framework support is limited to allow only an edge case scenario in authoring.

[dongle-the-gadget]

You can remove CsWinRT, leaving only Contracts and it would still work.