[Android] Fix CollectionView selection crash with HeaderTemplate

.github/copilot-instructions.md

@@ -138,6 +138,26 @@ When working with public API changes:
 - **Use `dotnet format analyzers`** if having trouble
 - **If files are incorrect**: Revert all changes, then add only the necessary new API entries
 
+**🚨 CRITICAL: `#nullable enable` must be line 1**
+
+Every `PublicAPI.Unshipped.txt` file starts with `#nullable enable` (often BOM-prefixed: `#nullable enable`) on the **first line**. If this line is moved or removed, the analyzer treats it as a declared API symbol and emits **RS0017** errors.
+
+**Never sort these files with plain `sort`** — the BOM bytes (`0xEF 0xBB 0xBF`) sort after ASCII characters under `LC_ALL=C`, pushing `#nullable enable` to the bottom of the file.
+
+When resolving merge conflicts or adding entries, use this safe pattern that preserves line 1:
+```bash
+for f in $(git diff --name-only --diff-filter=U | grep "PublicAPI.Unshipped.txt"); do
+  # Extract and preserve the #nullable enable line (with or without BOM)
+  HEADER=$(head -1 "$f" | grep -o '.*#nullable enable' || echo '#nullable enable')
+  # Strip conflict markers, remove all #nullable lines, sort+dedup the API entries
+  grep -v '^<<<<<<\|^======\|^>>>>>>\|#nullable enable' "$f" | LC_ALL=C sort -u | sed '/^$/d' > /tmp/api_fix.txt
+  # Reassemble: header first, then sorted entries
+  printf '%s\n' "$HEADER" > "$f"
+  cat /tmp/api_fix.txt >> "$f"
+  git add "$f"
+done
+```
+
 ### Branching
 - `main` - For bug fixes without API changes
 - `net10.0` - For new features and API changes

eng/pipelines/ci-device-tests.yml

@@ -5,6 +5,7 @@ trigger:
     - release/*
     - net*.0
     - inflight/*
+    - darc-*
   tags:
     include:
     - '*'

eng/pipelines/ci-uitests.yml

@@ -5,6 +5,7 @@ trigger:
     - release/*
     - net*.0
     - inflight/*
+    - darc-*
   tags:
     include:
     - '*'

src/Controls/src/Core/Handlers/Items/Android/Adapters/SelectableItemsViewAdapter.cs

@@ -28,6 +28,14 @@ public override void OnBindViewHolder(RecyclerView.ViewHolder holder, int positi
 				return;
 			}
 
+			// Header and footer view holders should not participate in selection tracking.
+			// They are not data items and calling GetItem() on their positions would cause
+			// an ArgumentOutOfRangeException due to the header index adjustment.
+			if (ItemsSource.IsHeader(position) || ItemsSource.IsFooter(position))
+			{
+				return;
+			}
+
 			// Watch for clicks so the user can select the item held by this ViewHolder
 			selectable.Clicked += SelectableClicked;
 

src/Controls/tests/TestCases.HostApp/Issues/Issue34120.cs

@@ -0,0 +1,81 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34120, "Label text truncated in ScrollView when MaxLines is set", PlatformAffected.Android)]
+public class Issue34120 : ContentPage
+{
+	// Reproduces the N3_Navigation layout: horizontal ScrollView with BindableLayout,
+	// 200×200 Border cards, Image (HeightRequest=120), and a Label with MaxLines=2.
+	record Issue34120MonkeyItem(string Name, string ImageUrl);
+
+	public Issue34120()
+	{
+		// Long names ("Golden Snub-nosed Monkey", "Tonkin Snub-nosed Monkey") are the ones
+		// that triggered truncation; "Baboon" is a short-name reference card.
+		var monkeys = new List<Issue34120MonkeyItem>
+		{
+			new("Golden Snub-nosed Monkey", "golden.jpg"),
+			new("Baboon",                   "papio.jpg"),
+			new("Tonkin Snub-nosed Monkey", "bluemonkey.jpg"),
+			new("Howler Monkey",            "alouatta.jpg"),
+			new("Squirrel Monkey",          "saimiri.jpg"),
+		};
+
+		var itemTemplate = new DataTemplate(() =>
+		{
+			var image = new Image
+			{
+				Aspect = Aspect.AspectFit,
+				HeightRequest = 120,
+				HorizontalOptions = LayoutOptions.Center,
+				VerticalOptions = LayoutOptions.Center,
+			};
+			image.SetBinding(Image.SourceProperty, "ImageUrl");
+
+			var nameLabel = new Label
+			{
+				FontSize = 14,
+				FontAttributes = FontAttributes.Bold,
+				BackgroundColor = Color.FromArgb("#AAFFFFFF"),
+				TextColor = Colors.Black,
+				Padding = new Thickness(4, 2),
+				HorizontalOptions = LayoutOptions.Center,
+				VerticalOptions = LayoutOptions.Center,
+				HorizontalTextAlignment = TextAlignment.Center,
+				LineBreakMode = LineBreakMode.WordWrap,
+				MaxLines = 2,
+			};
+			nameLabel.SetBinding(Label.TextProperty, "Name");
+			nameLabel.SetBinding(Label.AutomationIdProperty, "Name");
+
+			var card = new Border
+			{
+				Padding = new Thickness(10),
+				Stroke = Colors.LightGray,
+				StrokeThickness = 1,
+				WidthRequest = 200,
+				HeightRequest = 200,
+				BackgroundColor = Colors.White,
+				Content = new VerticalStackLayout
+				{
+					Spacing = 10,
+					Children = { image, nameLabel }
+				}
+			};
+			return card;
+		});
+
+		var horizontalStack = new HorizontalStackLayout
+		{
+			Spacing = 15,
+			Padding = new Thickness(5),
+		};
+		BindableLayout.SetItemTemplate(horizontalStack, itemTemplate);
+		BindableLayout.SetItemsSource(horizontalStack, monkeys);
+
+		Content = new ScrollView
+		{
+			Orientation = ScrollOrientation.Horizontal,
+			Content = horizontalStack,
+		};
+	}
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue34247.cs

@@ -0,0 +1,58 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34247, "CollectionView with HeaderTemplate and SelectionMode.Single crashes on selection", PlatformAffected.All)]
+public class Issue34247 : ContentPage
+{
+	public Issue34247()
+	{
+		var layout = new StackLayout();
+
+		var resultLabel = new Label()
+		{
+			Text = "Select an item to test",
+			AutomationId = "ResultLabel"
+		};
+
+		var items = new ObservableCollection<string> { "Item 1", "Item 2", "Item 3" };
+
+		var collectionView = new CollectionView()
+		{
+			SelectionMode = SelectionMode.Single,
+			AutomationId = "TestCollectionView",
+			HeightRequest = 300
+		};
+
+		collectionView.HeaderTemplate = new DataTemplate(() =>
+		{
+			return new Label
+			{
+				Text = "Header",
+				FontSize = 18,
+				FontAttributes = FontAttributes.Bold,
+				Margin = new Thickness(10)
+			};
+		});
+
+		collectionView.ItemTemplate = new DataTemplate(() =>
+		{
+			var label = new Label();
+			label.SetBinding(Label.TextProperty, ".");
+			label.Margin = new Thickness(10);
+			label.FontSize = 16;
+			return label;
+		});
+
+		collectionView.ItemsSource = items;
+		collectionView.SelectionChanged += (s, e) =>
+		{
+			resultLabel.Text = "Success";
+		};
+
+		layout.Children.Add(resultLabel);
+		layout.Children.Add(collectionView);
+
+		Content = layout;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34120.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34120 : _IssuesUITest
+{
+	public override string Issue => "Label text truncated in ScrollView when MaxLines is set";
+
+	public Issue34120(TestDevice device) : base(device) { }
+
+	[Test]
+	[Category(UITestCategories.Label)]
+	public void LabelNotTruncatedWithMaxLines()
+	{
+		// Wait for the page to load, then verify labels are not truncated.
+		App.WaitForElement("Golden Snub-nosed Monkey");
+		VerifyScreenshot();
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34247.cs

@@ -0,0 +1,26 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue34247 : _IssuesUITest
+	{
+		public Issue34247(TestDevice testDevice) : base(testDevice)
+		{
+		}
+
+		public override string Issue => "CollectionView with HeaderTemplate and SelectionMode.Single crashes on selection";
+
+		[Test]
+		[Category(UITestCategories.CollectionView)]
+		public void SelectingItemInCollectionViewWithHeaderTemplateDoesNotCrash()
+		{
+			App.WaitForElement("TestCollectionView");
+			App.WaitForElement("Item 1");
+			App.Tap("Item 1");
+			var result = App.WaitForElement("ResultLabel").GetText();
+			Assert.That(result, Is.EqualTo("Success"));
+		}
+	}
+}

src/Core/src/Handlers/Label/LabelHandler.Android.cs

@@ -22,9 +22,12 @@ public override Size GetDesiredSize(double widthConstraint, double heightConstra
 
 			// Android TextView reports full available width instead of actual text width when
 			// text wraps to multiple lines, causing incorrect positioning for non-Fill alignments.
+			// We narrow the desired width to the widest rendered line, but only when that narrowing
+			// won't cause re-wrapping that exceeds MaxLines and truncates visible text.
 			if (VirtualView.HorizontalLayoutAlignment != Primitives.LayoutAlignment.Fill &&
 				PlatformView?.Layout is Layout layout &&
-				layout.LineCount > 1)
+				layout.LineCount > 1 &&
+				PlatformView.Ellipsize == null)
 			{
 				float maxLineWidth = 0;
 				for (int i = 0; i < layout.LineCount; i++)
@@ -38,7 +41,33 @@ public override Size GetDesiredSize(double widthConstraint, double heightConstra
 				{
 					var actualWidth = Context.FromPixels(maxLineWidth + PlatformView.PaddingLeft + PlatformView.PaddingRight);
 					if (actualWidth < size.Width)
+					{
+						// When MaxLines is constrained, verify that narrowing doesn't cause the text
+						// to re-wrap into more lines than MaxLines allows (which would truncate text).
+						// Re-measure at exactly the pixel width the view will be arranged at.
+						if (PlatformView.MaxLines != int.MaxValue)
+						{
+							var narrowedPx = (int)Context.ToPixels(actualWidth);
+
+							// AtMost mirrors how the layout pass constrains width, ensuring the
+							// re-measurement reflects the same wrapping behaviour the view will
+							// experience when arranged at actualWidth.
+							PlatformView.Measure(
+								MeasureSpecMode.AtMost.MakeMeasureSpec(narrowedPx),
+								MeasureSpecMode.Unspecified.MakeMeasureSpec(0));
+
+							// Fail-safe: if Layout is null after re-measurement we cannot verify
+							// that truncation won't occur, so return the original size.
+							var measuredLayout = PlatformView.Layout;
+
+							if (measuredLayout is null || measuredLayout.LineCount > PlatformView.MaxLines)
+							{
+								return size; // Narrowing causes truncation (or unverifiable); return original size
+							}
+						}
+
 						return new Size(actualWidth, size.Height);
+					}
 				}
 			}
 

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

@@ -89,7 +89,7 @@ public void TouchesMoved(PointF[] points)
 		{
 			if (!_dragStarted)
 			{
-				if (points.Length == 1)
+				if (points.Length == 1 && _lastMovedViewPoints.Length > 0)
 				{
 					float deltaX = _lastMovedViewPoints[0].X - points[0].X;
 					float deltaY = _lastMovedViewPoints[0].Y - points[0].Y;