[Android] Fix GraphicsView dirtyRect mismatch when display density changes

src/Controls/tests/TestCases.HostApp/Issues/Issue34211.cs

@@ -0,0 +1,88 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34211, "Android display-size change causes parent and drawable children mismatch in .NET MAUI", PlatformAffected.Android)]
+public class Issue34211 : ContentPage
+{
+	readonly Issue34211_Drawable _drawable = new();
+	GraphicsView _graphicsView;
+	Label _statusLabel;
+
+	public Issue34211()
+	{
+		_graphicsView = new GraphicsView
+		{
+			AutomationId = "Issue34211_GraphicsView",
+			BackgroundColor = Color.FromArgb("#F0F0F0"),
+			Drawable = _drawable,
+		};
+
+		_statusLabel = new Label
+		{
+			AutomationId = "Issue34211_StatusLabel",
+			Text = "Waiting for first draw...",
+			HorizontalOptions = LayoutOptions.Center,
+			Margin = new Thickness(0, 0, 0, 10),
+		};
+
+		var checkButton = new Button
+		{
+			AutomationId = "Issue34211_CheckButton",
+			Text = "Check Size Match",
+		};
+		checkButton.Clicked += (_, _) => _graphicsView.Invalidate();
+
+		Content = new Grid
+		{
+			Padding = 20,
+			RowDefinitions =
+			{
+				new RowDefinition { Height = GridLength.Auto },
+				new RowDefinition { Height = GridLength.Auto },
+				new RowDefinition { Height = GridLength.Star },
+			},
+			Children =
+			{
+				_statusLabel,
+				checkButton,
+				_graphicsView,
+			}
+		};
+
+		Grid.SetRow(_statusLabel, 0);
+		Grid.SetRow(checkButton, 1);
+		Grid.SetRow(_graphicsView, 2);
+
+		_graphicsView.SizeChanged += (_, _) => _graphicsView.Invalidate();
+
+		_drawable.OnDrawn = rect =>
+		{
+			MainThread.BeginInvokeOnMainThread(() =>
+			{
+				double viewW = _graphicsView.Width;
+				double viewH = _graphicsView.Height;
+				bool widthMatch = Math.Abs(viewW - rect.Width) <= 1.0;
+				bool heightMatch = Math.Abs(viewH - rect.Height) <= 1.0;
+				_statusLabel.Text = widthMatch && heightMatch
+					? "PASS: sizes match"
+					: $"FAIL: GraphicsView={viewW:F1}x{viewH:F1} Drawable={rect.Width:F1}x{rect.Height:F1}";
+			});
+		};
+	}
+}
+
+public class Issue34211_Drawable : IDrawable
+{
+	public Action<RectF> OnDrawn { get; set; }
+
+	public void Draw(ICanvas canvas, RectF dirtyRect)
+	{
+		canvas.FillColor = Colors.CornflowerBlue;
+		canvas.FillRectangle(dirtyRect);
+
+		canvas.StrokeColor = Colors.DarkBlue;
+		canvas.StrokeSize = 3;
+		canvas.DrawRectangle(dirtyRect);
+
+		OnDrawn?.Invoke(dirtyRect);
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34211.cs

@@ -0,0 +1,49 @@
+#if ANDROID // Android-only: display-density change can only be triggered via adb shell wm density.
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34211 : _IssuesUITest
+{
+	public Issue34211(TestDevice device) : base(device) { }
+
+	public override string Issue => "Android display-size change causes parent and drawable children mismatch in .NET MAUI";
+
+	[Test]
+	[Category(UITestCategories.GraphicsView)]
+	public void DrawableDirtyRectMatchesGraphicsViewSizeAfterDisplayDensityChange()
+	{
+		App.WaitForElement("Issue34211_GraphicsView");
+
+		string originalDensity = ShellHelper.ExecuteShellCommandWithOutput("adb shell wm density").Trim();
+		try
+		{
+			App.BackgroundApp();
+			ShellHelper.ExecuteShellCommand($"adb shell wm density {(originalDensity.Contains("320", StringComparison.Ordinal) ? "280" : "320")}");
+			App.ForegroundApp();
+
+			// adb shell wm density triggers an Activity recreation because density is not listed
+			// in MAUI's android:configChanges. The app restarts at the list page, so re-navigate.
+			App.WaitForElement("SearchBar");
+			App.ClearText("SearchBar");
+			App.EnterText("SearchBar", Issue);
+			App.WaitForElement("GoToTestButton");
+			App.Tap("GoToTestButton");
+
+			var el = App.WaitForElement(() =>
+			{
+				var e = App.FindElement("Issue34211_StatusLabel");
+				var text = e?.GetText() ?? string.Empty;
+				return text.StartsWith("PASS", StringComparison.Ordinal) || text.StartsWith("FAIL", StringComparison.Ordinal) ? e : null;
+			}, "Timed out waiting for draw after density change");
+			Assert.That(el.GetText(), Does.StartWith("PASS"), "GraphicsView and drawable sizes diverged after display-density change");
+		}
+		finally
+		{
+			ShellHelper.ExecuteShellCommand("adb shell wm density reset");
+		}
+	}
+}
+#endif

src/Core/src/Platform/Android/PlatformTouchGraphicsView.cs

@@ -19,14 +19,19 @@ public class PlatformTouchGraphicsView : PlatformGraphicsView
 
 		public PlatformTouchGraphicsView(Context context) : base(context)
 		{
-			_scale = (context ?? global::Android.App.Application.Context)?.Resources?.DisplayMetrics?.Density ?? 1;
 		}
 
+		// Override to use MAUI's cached density (Context.GetDisplayDensity) so that
+		// dirtyRect, touch coords and _bounds stay consistent with GraphicsView.Width/Height.
+		internal override float GetDisplayDensity() => Context!.GetDisplayDensity();
+
 		protected override void OnLayout(bool changed, int left, int top, int right, int bottom)
 		{
 			base.OnLayout(changed, left, top, right, bottom);
 			if (changed)
 			{
+				// Cache density once per layout; reused by touch/hover events until next layout.
+				_scale = GetDisplayDensity();
 				var width = right - left;
 				var height = bottom - top;
 				_bounds = new RectF(0, 0, width / _scale, height / _scale);

src/Graphics/src/Graphics/Platforms/Android/PlatformGraphicsView.cs

@@ -12,7 +12,7 @@ public class PlatformGraphicsView : View
 		private readonly PlatformCanvas _canvas;
 		private readonly ScalingCanvas _scalingCanvas;
 		private IDrawable _drawable;
-		private readonly float _scale = 1;
+		private float _scale;
 		private Color _backgroundColor;
 
 		public PlatformGraphicsView(Context context, IAttributeSet attrs, IDrawable drawable = null) : base(context, attrs)
@@ -31,6 +31,9 @@ public PlatformGraphicsView(Context context, IDrawable drawable = null) : base(c
 			Drawable = drawable;
 		}
 
+		// Overridden by friend assemblies to supply the density source used for draw scaling.
+		internal virtual float GetDisplayDensity() => Resources.DisplayMetrics.Density;
+
 		public Color BackgroundColor
 		{
 			get => _backgroundColor;
@@ -78,6 +81,7 @@ public override void Draw(Canvas androidCanvas)
 		protected override void OnSizeChanged(int width, int height, int oldWidth, int oldHeight)
 		{
 			base.OnSizeChanged(width, height, oldWidth, oldHeight);
+			_scale = GetDisplayDensity();
 			_width = width;
 			_height = height;
 		}