Fix CollectionView grid spacing updates for first row and column

src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs

@@ -484,26 +484,9 @@ protected virtual void UpdateItemSpacing()
 
 			if (_itemDecoration is SpacingItemDecoration spacingDecoration)
 			{
-				// SpacingItemDecoration now removes spacing on outer edges (first/last row or column),
-				// so we only need negative padding on the cross-axis for grid layouts to compensate
-				// for the spacing between columns (vertical grid) or rows (horizontal grid).
-				if (ItemsLayout is GridItemsLayout gridItemsLayout)
-				{
-					if (gridItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal)
-					{
-						var verticalPadding = -spacingDecoration.VerticalOffset;
-						SetPadding(0, verticalPadding, 0, verticalPadding);
-					}
-					else
-					{
-						var horizontalPadding = -spacingDecoration.HorizontalOffset;
-						SetPadding(horizontalPadding, 0, horizontalPadding, 0);
-					}
-				}
-				else
-				{
-					SetPadding(0, 0, 0, 0);
-				}
+				var horizontalPadding = ItemsLayout is GridItemsLayout ? 0 : -spacingDecoration.HorizontalOffset;
+				var verticalPadding = ItemsLayout is GridItemsLayout ? 0 : -spacingDecoration.VerticalOffset;
+				SetPadding(horizontalPadding, verticalPadding, horizontalPadding, verticalPadding);
 			}
 		}
 

src/Controls/tests/TestCases.HostApp/Issues/Issue34257.cs

@@ -0,0 +1,166 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34257, "CollectionView vertical grid item spacing updates all rows and columns", PlatformAffected.Android | PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue34257 : ContentPage
+{
+	readonly GridItemsLayout _itemsLayout;
+	readonly Label _statusLabel;
+
+	public Issue34257()
+	{
+		_itemsLayout = new GridItemsLayout(2, ItemsLayoutOrientation.Vertical)
+		{
+			HorizontalItemSpacing = 0,
+			VerticalItemSpacing = 0
+		};
+
+		_statusLabel = new Label
+		{
+			AutomationId = "StatusLabel",
+			Text = "Spacing=0,0"
+		};
+
+		var applySpacingButton = new Button
+		{
+			AutomationId = "ApplyHorizontalSpacingButton",
+			Text = "Apply horizontal spacing"
+		};
+		applySpacingButton.Clicked += OnApplyHorizontalSpacingClicked;
+
+		var applyVerticalSpacingButton = new Button
+		{
+			AutomationId = "ApplyVerticalSpacingButton",
+			Text = "Apply vertical spacing"
+		};
+		applyVerticalSpacingButton.Clicked += OnApplyVerticalSpacingClicked;
+
+		var collectionView = new CollectionView
+		{
+			AutomationId = "TestCollectionView",
+			HeightRequest = 260,
+			HorizontalOptions = LayoutOptions.Center,
+			ItemsLayout = _itemsLayout,
+			ItemsSource = CreateItems(),
+			ItemSizingStrategy = ItemSizingStrategy.MeasureAllItems,
+			SelectionMode = SelectionMode.None,
+			WidthRequest = 340
+		};
+		collectionView.ItemTemplate = new DataTemplate(() =>
+		{
+			var titleLabel = new Label
+			{
+				FontAttributes = FontAttributes.Bold,
+				LineBreakMode = LineBreakMode.TailTruncation
+			};
+			titleLabel.SetBinding(Label.TextProperty, nameof(SpacingIssueItem.Name));
+
+			var locationLabel = new Label
+			{
+				FontAttributes = FontAttributes.Italic,
+				LineBreakMode = LineBreakMode.TailTruncation,
+				VerticalOptions = LayoutOptions.End
+			};
+			locationLabel.SetBinding(Label.TextProperty, nameof(SpacingIssueItem.Location));
+
+			var textLayout = new Grid
+			{
+				RowDefinitions =
+				{
+					new RowDefinition { Height = GridLength.Auto },
+					new RowDefinition { Height = GridLength.Auto }
+				}
+			};
+			textLayout.Add(titleLabel);
+			textLayout.Add(locationLabel, 0, 1);
+
+			var root = new Grid
+			{
+				ColumnDefinitions =
+				{
+					new ColumnDefinition { Width = 70 },
+					new ColumnDefinition { Width = GridLength.Star }
+				},
+				Padding = 10
+			};
+			root.SetBinding(AutomationIdProperty, nameof(SpacingIssueItem.AutomationId));
+			root.SetBinding(BackgroundColorProperty, nameof(SpacingIssueItem.BackgroundColor));
+
+			var imagePlaceholder = new Border
+			{
+				Background = Colors.DarkSlateBlue,
+				HeightRequest = 60,
+				StrokeThickness = 0,
+				VerticalOptions = LayoutOptions.Center,
+				WidthRequest = 60
+			};
+
+			root.Add(imagePlaceholder);
+			root.Add(textLayout, 1, 0);
+
+			return root;
+		});
+
+		Content = new ScrollView
+		{
+			Content = new VerticalStackLayout
+			{
+				Padding = 20,
+				Spacing = 12,
+				Children =
+				{
+					new Label { Text = "Issue 34257 reproduces a spacing update bug in a two-column vertical CollectionView grid." },
+					new Label { Text = "Apply horizontal or vertical spacing and verify both columns and rows resize consistently." },
+					new HorizontalStackLayout
+					{
+						Spacing = 12,
+						Children =
+						{
+							applySpacingButton,
+							applyVerticalSpacingButton
+						}
+					},
+					_statusLabel,
+					collectionView
+				}
+			}
+		};
+	}
+
+	void OnApplyHorizontalSpacingClicked(object sender, EventArgs e)
+	{
+		_itemsLayout.VerticalItemSpacing = 0;
+		_itemsLayout.HorizontalItemSpacing = 80;
+		_statusLabel.Text = "Spacing=0,80";
+	}
+
+	void OnApplyVerticalSpacingClicked(object sender, EventArgs e)
+	{
+		_itemsLayout.VerticalItemSpacing = 40;
+		_itemsLayout.HorizontalItemSpacing = 0;
+		_statusLabel.Text = "Spacing=40,0";
+	}
+
+	static ObservableCollection<SpacingIssueItem> CreateItems()
+	{
+		return
+		[
+			new SpacingIssueItem("FirstColumnTopItem", "Capuchin", "Central America", Colors.LightSkyBlue),
+			new SpacingIssueItem("SecondColumnTopItem", "Spider", "South America", Colors.LightSalmon),
+			new SpacingIssueItem("FirstColumnBottomItem", "Howler", "South America", Colors.PaleGreen),
+			new SpacingIssueItem("SecondColumnBottomItem", "Baboon", "Africa", Colors.Khaki)
+		];
+	}
+
+	class SpacingIssueItem(string automationId, string name, string location, Color backgroundColor)
+	{
+		public string AutomationId { get; } = automationId;
+
+		public Color BackgroundColor { get; } = backgroundColor;
+
+		public string Location { get; } = location;
+
+		public string Name { get; } = name;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34257.cs

@@ -0,0 +1,39 @@
+#if TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34257 : _IssuesUITest
+{
+	public Issue34257(TestDevice device)
+		: base(device)
+	{
+	}
+
+	public override string Issue => "CollectionView vertical grid item spacing updates all rows and columns";
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void UpdatingHorizontalSpacingShouldResizeBothColumns()
+	{
+		var firstColumnBefore = App.WaitForElement("FirstColumnTopItem").GetRect();
+		App.Tap("ApplyHorizontalSpacingButton");
+		App.WaitForElement("StatusLabel", "Spacing=0,80");
+		var firstColumnAfter = App.WaitForElement("FirstColumnTopItem").GetRect();
+		Assert.That(firstColumnBefore.X, Is.Not.EqualTo(firstColumnAfter.X), $"Expected the first column to move");
+	}
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void UpdatingVerticalSpacingShouldResizeBothRows()
+	{
+		var firstColumnBefore = App.WaitForElement("FirstColumnTopItem").GetRect();
+		App.Tap("ApplyVerticalSpacingButton");
+		App.WaitForElement("StatusLabel", "Spacing=40,0");
+		var firstColumnAfter = App.WaitForElement("FirstColumnTopItem").GetRect();
+		Assert.That(firstColumnBefore.Y, Is.Not.EqualTo(firstColumnAfter.Y), $"Expected the first row to move");
+	}
+}
+#endif