Fix Media Element Full Screen in Windows when using Multiple Windows (#2506)

* Switch from using `page.GetParentWindow` to user32.dll `GetForegroundWindow` for grabbing correct window in multi-window environment

* Update src/CommunityToolkit.Maui.MediaElement/Views/MauiMediaElement.windows.cs

Co-authored-by: Copilot <[email protected]>

* Update method for Getting `AppWindow` to use `TryGetForeGroundWindow()` and if it is null throw InvalidOperationException if window is null.

---------

Co-authored-by: Brandon Minnick <[email protected]>
Co-authored-by: Copilot <[email protected]>

Author: 3 people

src/CommunityToolkit.Maui.MediaElement/CommunityToolkit.Maui.MediaElement.csproj

@@ -7,6 +7,8 @@
     <SingleProject>true</SingleProject>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <IsAotCompatible>true</IsAotCompatible>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    
 
     <SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'ios'">15.0</SupportedOSPlatformVersion>
     <SupportedOSPlatformVersion Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'maccatalyst'">15.0</SupportedOSPlatformVersion>

src/CommunityToolkit.Maui.MediaElement/Views/MauiMediaElement.windows.cs

@@ -1,4 +1,5 @@
 using System.Reflection;
+using System.Runtime.InteropServices;
 using CommunityToolkit.Maui.Extensions;
 using CommunityToolkit.Maui.Primitives;
 using CommunityToolkit.Maui.Views;
@@ -8,7 +9,6 @@
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Controls.Primitives;
 using Microsoft.UI.Xaml.Markup;
-using WinRT.Interop;
 using Application = Microsoft.Maui.Controls.Application;
 using Grid = Microsoft.UI.Xaml.Controls.Grid;
 using Page = Microsoft.Maui.Controls.Page;
@@ -20,7 +20,17 @@ namespace CommunityToolkit.Maui.Core.Views;
 /// </summary>
 public partial class MauiMediaElement : Grid, IDisposable
 {
-	static readonly AppWindow appWindow = GetAppWindowForCurrentWindow();
+	[LibraryImport("user32.dll")]
+	internal static partial IntPtr GetForegroundWindow();
+
+	/// <summary>
+	/// Safely gets the foreground window handle, returning null if no foreground window exists.
+	/// </summary>
+	internal static IntPtr? TryGetForegroundWindow()
+	{
+		var hwnd = GetForegroundWindow();
+		return hwnd == IntPtr.Zero ? null : hwnd;
+	}
 	readonly Popup popup = new();
 	readonly Grid fullScreenGrid = new();
 	readonly MediaPlayerElement mediaPlayerElement;
@@ -157,24 +167,16 @@ protected virtual void Dispose(bool disposing)
 
 	static AppWindow GetAppWindowForCurrentWindow()
 	{
-		// let's cache the CurrentPage here, since the user can navigate or background the app
-		// while this method is running
-		var currentPage = CurrentPage;
-
-		if (currentPage?.GetParentWindow().Handler.PlatformView is not MauiWinUIWindow window)
-		{
-			throw new InvalidOperationException($"{nameof(window)} cannot be null.");
-		}
-
-		var handle = WindowNative.GetWindowHandle(window);
-		var id = Win32Interop.GetWindowIdFromWindow(handle);
-
+		var windowHandle = TryGetForegroundWindow() ?? throw new InvalidOperationException("No foreground window found.");
+		var id = Win32Interop.GetWindowIdFromWindow(windowHandle);
 		return AppWindow.GetFromWindowId(id);
 	}
 
 	void OnFullScreenButtonClick(object sender, RoutedEventArgs e)
 	{
 		var currentPage = CurrentPage;
+		var appWindow = GetAppWindowForCurrentWindow();
+
 		if (appWindow.Presenter.Kind is AppWindowPresenterKind.FullScreen)
 		{
 			appWindow.SetPresenter(AppWindowPresenterKind.Default);