众所周知，UWP 使用的窗口模型是 CoreWindow，但是 UWP 本身只是一个应用模型，所以完全可以创建 win32 窗口，那么我们可以不可以创建一个 win32 窗口，然后像 XAML 岛 (XAML Islands) 一样把 XAML 托管上去呢？本篇将讲述如何利用 WAS (Windows App SDK，俗称 WinUI3) 在 UWP 创建一个 XAML 岛窗口。
演示视频：https://x.com/wherewhere7/status/1721570411388039587
由于 WAS 在 win32 应用模型下本身就是个 XAML 岛，所以 WAS 对 XAML 岛的支持要比 WUXC (Windows.UI.Xaml.Controls) 要好多了，接下来的内容大多是将 WAS 中实现窗口的方法迁移到 C#。
首先，不管是 WUXC 还是 WAS 的 XAML 岛都会判断当前的应用模型是否为ClassicDesktop，所以我们需要利用Detours劫持AppPolicyGetWindowingModel方法。具体内容如下：
#r "nuget:Detours.Win32Metadata"
#r "nuget:Microsoft.Windows.CsWin32"using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using Windows.Win32;
using Windows.Win32.Foundation;
using Windows.Win32.Storage.Packaging.Appx;
using Detours = Microsoft.Detours.PInvoke;/// <summary>
/// Represents a hook for the <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function.
/// </summary>
public sealed partial class HookWindowingModel : IDisposable
{/// <summary>/// The value that indicates whether the class has been disposed./// </summary>private bool disposed;/// <summary>/// The reference count for the hook./// </summary>private static int refCount;/// <summary>/// The value that represents the current process token./// </summary>private const int currentProcessToken = -6;/// <remarks>The original <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function.</remarks>/// <inheritdoc cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/>private static unsafe delegate* unmanaged[Stdcall]<HANDLE, AppPolicyWindowingModel*, WIN32_ERROR> AppPolicyGetWindowingModel;/// <summary>/// Initializes a new instance of the <see cref="HookWindowingModel"/> class./// </summary>public HookWindowingModel(){refCount++;StartHook();}/// <summary>/// Finalizes this instance of the <see cref="HookWindowingModel"/> class./// </summary>~HookWindowingModel(){Dispose();}/// <summary>/// Gets the value that indicates whether the hook is active./// </summary>public static bool IsHooked { get; private set; }/// <summary>/// Gets or sets the windowing model to use when the hooked <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function is called./// </summary>internal static AppPolicyWindowingModel WindowingModel { get; set; } = AppPolicyWindowingModel.AppPolicyWindowingModel_ClassicDesktop;/// <summary>/// Starts the hook for the <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function./// </summary>private static unsafe void StartHook(){if (!IsHooked){using FreeLibrarySafeHandle library = PInvoke.GetModuleHandle("KERNEL32.dll");if (!library.IsInvalid && NativeLibrary.TryGetExport(library.DangerousGetHandle(), nameof(PInvoke.AppPolicyGetWindowingModel), out nint appPolicyGetWindowingModel)){void* appPolicyGetWindowingModelPtr = (void*)appPolicyGetWindowingModel;delegate* unmanaged[Stdcall]<HANDLE, AppPolicyWindowingModel*, WIN32_ERROR> overrideAppPolicyGetWindowingModel = &OverrideAppPolicyGetWindowingModel;_ = Detours.DetourRestoreAfterWith();_ = Detours.DetourTransactionBegin();_ = Detours.DetourUpdateThread(PInvoke.GetCurrentThread());_ = Detours.DetourAttach(ref appPolicyGetWindowingModelPtr, overrideAppPolicyGetWindowingModel);_ = Detours.DetourTransactionCommit();AppPolicyGetWindowingModel = (delegate* unmanaged[Stdcall]<HANDLE, AppPolicyWindowingModel*, WIN32_ERROR>)appPolicyGetWindowingModelPtr;IsHooked = true;}}}/// <summary>/// Ends the hook for the <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function./// </summary>private static unsafe void EndHook(){if (--refCount == 0 && IsHooked){void* appPolicyGetWindowingModelPtr = AppPolicyGetWindowingModel;delegate* unmanaged[Stdcall]<HANDLE, AppPolicyWindowingModel*, WIN32_ERROR> overrideAppPolicyGetWindowingModel = &OverrideAppPolicyGetWindowingModel;_ = Detours.DetourTransactionBegin();_ = Detours.DetourUpdateThread(PInvoke.GetCurrentThread());_ = Detours.DetourDetach(&appPolicyGetWindowingModelPtr, overrideAppPolicyGetWindowingModel);_ = Detours.DetourTransactionCommit();AppPolicyGetWindowingModel = null;IsHooked = false;}}/// <param name="policy">A pointer to a variable of the <a href="https://docs.microsoft.com/windows/win32/api/appmodel/ne-appmodel-apppolicywindowingmodel">AppPolicyWindowingModel</a> enumerated type./// When the function returns successfully, the variable contains the <see cref="WindowingModel"/> when the identified process is current; otherwise, the windowing model of the identified process.</param>/// <remarks>The overridden <see cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/> function.</remarks>/// <inheritdoc cref="PInvoke.AppPolicyGetWindowingModel(HANDLE, AppPolicyWindowingModel*)"/>[UnmanagedCallersOnly(CallConvs = [typeof(CallConvStdcall)])]private static unsafe WIN32_ERROR OverrideAppPolicyGetWindowingModel(HANDLE processToken, AppPolicyWindowingModel* policy){if ((int)processToken.Value == currentProcessToken){*policy = WindowingModel;return WIN32_ERROR.ERROR_SUCCESS;}return AppPolicyGetWindowingModel(processToken, policy);}/// <inheritdoc/>public void Dispose(){if (!disposed && IsHooked){EndHook();}GC.SuppressFinalize(this);disposed = true;}
}准备工作完成，接下来我们就可以创建窗口了，首先我们需要新创建一个线程，CoreWindow 线程无法新建 XAML 岛，不过在 XAML 岛线程可以，新建线程只需要用Thread就行了。
new Thread(() => { ... });WAS 提供了AppWindow来管理 win32 窗口，我们只需要使用它创建一个窗口就行了。
AppWindow window = AppWindow.Create();接下来我们需要创建 XAML 岛，这时我们就需要利用上面劫持器来劫持获取应用模型的方法了。
DispatcherQueueController controller;
DesktopWindowXamlSource source;using (HookWindowingModel hook = new())
{controller = DispatcherQueueController.CreateOnCurrentThread();source = new DesktopWindowXamlSource();
}然后我们就可以把 XAML 岛糊到之前创建的 AppWindow 上了。
source.Initialize(window.Id);
DesktopChildSiteBridge bridge = source.SiteBridge;
bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;
bridge.Show();DispatcherQueue dispatcherQueue = controller.DispatcherQueue;
window.AssociateWithDispatcherQueue(dispatcherQueue);由于 XAML 岛存在的一些特性，当窗口扩展标题栏或者全屏化的是否窗口内容并不会跟着变化，所以我们需要一些小魔法来让它在变化时调整大小。
window.Changed += (sender, args) =>
{if (args.DidPresenterChange){bridge.ResizePolicy = ContentSizePolicy.None;bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;}
};最后不要忘了保持当前线程，不然这里跑完了窗口就退出了。
dispatcherQueue.RunEventLoop();
await controller.ShutdownQueueAsync();当窗口关闭后记得执行DispatcherQueue.EnqueueEventLoopExit()来释放保持的线程。
最后把之前的东西组合起来，再加点东西：
/// <summary>
/// Create a new <see cref="DesktopWindow"/> instance.
/// </summary>
/// <param name="launched">Do something after <see cref="DesktopWindowXamlSource"/> created.</param>
/// <returns>The new instance of <see cref="DesktopWindow"/>.</returns>
public static Task<DesktopWindow> CreateAsync(Action<DesktopWindowXamlSource> launched)
{TaskCompletionSource<DesktopWindow> taskCompletionSource = new();new Thread(async () =>{try{DispatcherQueueController controller;DesktopWindowXamlSource source;AppWindow window = AppWindow.Create();using (HookWindowingModel hook = new()){controller = DispatcherQueueController.CreateOnCurrentThread();source = new DesktopWindowXamlSource();}source.Initialize(window.Id);DesktopChildSiteBridge bridge = source.SiteBridge;bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;bridge.Show();window.Changed += (sender, args) =>{if (args.DidPresenterChange){bridge.ResizePolicy = ContentSizePolicy.None;bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;}};DispatcherQueue dispatcherQueue = controller.DispatcherQueue;window.AssociateWithDispatcherQueue(dispatcherQueue);TrackWindow(window);launched(source);DesktopWindow desktopWindow = new(){AppWindow = window,WindowXamlSource = source};taskCompletionSource.SetResult(desktopWindow);dispatcherQueue.RunEventLoop();await controller.ShutdownQueueAsync();}catch (Exception e){taskCompletionSource.SetException(e);}}){Name = nameof(DesktopWindowXamlSource)}.Start();return taskCompletionSource.Task;
}/// <summary>
/// Create a new <see cref="DesktopWindow"/> instance.
/// </summary>
/// <param name="dispatcherQueue">The <see cref="DispatcherQueue"/> to provide thread.</param>
/// <param name="launched">Do something after <see cref="DesktopWindowXamlSource"/> created.</param>
/// <returns>The new instance of <see cref="DesktopWindow"/>.</returns>
public static Task<DesktopWindow> CreateAsync(DispatcherQueue dispatcherQueue, Action<DesktopWindowXamlSource> launched)
{TaskCompletionSource<DesktopWindow> taskCompletionSource = new();_ = dispatcherQueue.TryEnqueue(() =>{try{DesktopWindowXamlSource source;AppWindow window = AppWindow.Create();window.AssociateWithDispatcherQueue(dispatcherQueue);TrackWindow(window);using (HookWindowingModel hook = new()){source = new DesktopWindowXamlSource();}source.Initialize(window.Id);DesktopChildSiteBridge bridge = source.SiteBridge;bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;bridge.Show();window.Changed += (sender, args) =>{if (args.DidPresenterChange){bridge.ResizePolicy = ContentSizePolicy.None;bridge.ResizePolicy = ContentSizePolicy.ResizeContentToParentWindow;}};launched(source);DesktopWindow desktopWindow = new(){AppWindow = window,WindowXamlSource = source};taskCompletionSource.SetResult(desktopWindow);}catch (Exception e){taskCompletionSource.SetException(e);}});return taskCompletionSource.Task;
}private static void TrackWindow(AppWindow window)
{if (ActiveDesktopWindows.ContainsKey(window.DispatcherQueue)){ActiveDesktopWindows[window.DispatcherQueue] += 1;}else{ActiveDesktopWindows[window.DispatcherQueue] = 1;}window.Destroying -= AppWindow_Destroying;window.Destroying += AppWindow_Destroying;
}private static void AppWindow_Destroying(AppWindow sender, object args)
{if (ActiveDesktopWindows.TryGetValue(sender.DispatcherQueue, out ulong num)){num--;if (num == 0){ActiveDesktopWindows.Remove(sender.DispatcherQueue);sender.DispatcherQueue.EnqueueEventLoopExit();return;}ActiveDesktopWindows[sender.DispatcherQueue] = num;}
}private static Dictionary<DispatcherQueue, ulong> ActiveDesktopWindows { get; } = [];其中DesktopWindow是用来存放 AppWindow 和 DesktopWindowXamlSource的类，如果不嫌麻烦的话可以包裹成一个和 Microsoft.UI.Xaml.Window一样的东西。
最后附上示例应用：https://github.com/wherewhere/CoreAppUWP/tree/muxc
