[Windows] Fixed KeepLastItemInView Behavior Not Working as Expected in CarouselView

src/Controls/src/Core/Handlers/Items/CarouselViewHandler.Windows.cs

@@ -15,6 +15,8 @@
 using WScrollMode = Microsoft.UI.Xaml.Controls.ScrollMode;
 using WSnapPointsAlignment = Microsoft.UI.Xaml.Controls.Primitives.SnapPointsAlignment;
 using WSnapPointsType = Microsoft.UI.Xaml.Controls.SnapPointsType;
+using WSetter = Microsoft.UI.Xaml.Setter;
+using WStyle = Microsoft.UI.Xaml.Style;
 
 namespace Microsoft.Maui.Controls.Handlers.Items
 {
@@ -26,6 +28,7 @@ public partial class CarouselViewHandler : ItemsViewHandler<CarouselView>
 		WScrollBarVisibility? _verticalScrollBarVisibilityWithoutLoop;
 		Size _currentSize;
 		bool _isCarouselViewReady;
+		bool _isInternalPositionUpdate;
 		int _gotoPosition = -1;
 		NotifyCollectionChangedEventHandler _collectionChanged;
 		readonly WeakNotifyCollectionChangedProxy _proxy = new();
@@ -146,7 +149,7 @@ protected override ItemsViewScrolledEventArgs ComputeVisibleIndexes(ItemsViewScr
 		{
 			args = base.ComputeVisibleIndexes(args, orientation, advancing);
 
-			if (ItemsView.Loop && ItemsView.ItemsSource is not null)
+			if (ItemsView.Loop && ItemsView.ItemsSource is not null && ItemCount > 0)
 			{
 				args.FirstVisibleItemIndex %= ItemCount;
 				args.CenterItemIndex %= ItemCount;
@@ -156,6 +159,21 @@ protected override ItemsViewScrolledEventArgs ComputeVisibleIndexes(ItemsViewScr
 			return args;
 		}
 
+		protected override void UpdateEmptyViewVisibility()
+		{
+			if (ItemsView?.Loop == true)
+			{
+				bool isEmpty = (CollectionViewSource?.View?.Count ?? 0) == 0;
+				var targetTemplate = isEmpty ? null : CarouselItemsViewTemplate;
+				if (ListViewBase.ItemTemplate != targetTemplate)
+				{
+					ListViewBase.ItemTemplate = targetTemplate;
+				}
+			}
+
+			base.UpdateEmptyViewVisibility();
+		}
+
 		ListViewBase CreateCarouselListLayout(ItemsLayoutOrientation layoutOrientation)
 		{
 			UI.Xaml.Controls.ListView listView;
@@ -165,7 +183,8 @@ ListViewBase CreateCarouselListLayout(ItemsLayoutOrientation layoutOrientation)
 				listView = new FormsListView()
 				{
 					Style = (UI.Xaml.Style)WApp.Current.Resources["HorizontalCarouselListStyle"],
-					ItemsPanel = (ItemsPanelTemplate)WApp.Current.Resources["HorizontalListItemsPanel"]
+					ItemsPanel = (ItemsPanelTemplate)WApp.Current.Resources["HorizontalListItemsPanel"],
+					ItemContainerStyle = GetItemContainerStyle(true)
 				};
 
 				ScrollViewer.SetHorizontalScrollBarVisibility(listView, WScrollBarVisibility.Auto);
@@ -175,7 +194,8 @@ ListViewBase CreateCarouselListLayout(ItemsLayoutOrientation layoutOrientation)
 			{
 				listView = new FormsListView()
 				{
-					Style = (UI.Xaml.Style)WApp.Current.Resources["VerticalCarouselListStyle"]
+					Style = (UI.Xaml.Style)WApp.Current.Resources["VerticalCarouselListStyle"],
+					ItemContainerStyle = GetItemContainerStyle(false)
 				};
 
 				ScrollViewer.SetHorizontalScrollBarVisibility(listView, WScrollBarVisibility.Disabled);
@@ -289,7 +309,7 @@ double GetItemWidth()
 
 			if (CarouselItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal)
 			{
-				itemWidth = ListViewBase.ActualWidth - ItemsView.PeekAreaInsets.Left - ItemsView.PeekAreaInsets.Right;
+				itemWidth = ListViewBase.ActualWidth - ItemsView.PeekAreaInsets.Left - ItemsView.PeekAreaInsets.Right - ItemsView.ItemsLayout.ItemSpacing;
 			}
 
 			return Math.Max(itemWidth, 0);
@@ -301,7 +321,7 @@ double GetItemHeight()
 
 			if (CarouselItemsLayout.Orientation == ItemsLayoutOrientation.Vertical)
 			{
-				itemHeight = ListViewBase.ActualHeight - ItemsView.PeekAreaInsets.Top - ItemsView.PeekAreaInsets.Bottom;
+				itemHeight = ListViewBase.ActualHeight - ItemsView.PeekAreaInsets.Top - ItemsView.PeekAreaInsets.Bottom - ItemsView.ItemsLayout.ItemSpacing;
 			}
 
 			return Math.Max(itemHeight, 0);
@@ -334,9 +354,7 @@ bool IsValidPosition(int position)
 		void SetCarouselViewPosition(int position)
 		{
 			if (ItemCount == 0)
-			{
 				return;
-			}
 
 			if (!IsValidPosition(position))
 				return;
@@ -408,7 +426,10 @@ void UpdateCurrentItem()
 
 			var currentItemPosition = GetItemPositionInCarousel(ItemsView.CurrentItem);
 
-			if (currentItemPosition < 0 || currentItemPosition >= ItemCount)
+			bool isOutOfBounds = currentItemPosition < 0 || currentItemPosition >= ItemCount;
+			bool isSamePosition = ItemsView.Position == currentItemPosition;
+
+			if (isOutOfBounds || isSamePosition)
 			{
 				return;
 			}
@@ -418,7 +439,9 @@ void UpdateCurrentItem()
 				return;
 			}
 
-			ItemsView.ScrollTo(currentItemPosition, position: ScrollToPosition.Center, animate: ItemsView.AnimateCurrentItemChanges);
+			// Disable animation during collection changes to prevent cascading scroll events
+			var animate = ItemsView.AnimateCurrentItemChanges && !_isInternalPositionUpdate;
+			ItemsView.ScrollTo(currentItemPosition, position: ScrollToPosition.Center, animate: animate);
 		}
 
 		void UpdatePosition()
@@ -566,34 +589,53 @@ void OnScrollViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
 
 		void OnCollectionItemsSourceChanged(object sender, NotifyCollectionChangedEventArgs e)
 		{
-			var carouselPosition = ItemsView.Position;
-			var currentItemPosition = GetItemPositionInCarousel(ItemsView.CurrentItem);
-			var count = (sender as IList).Count;
+			// Set flag to disable animation during collection changes
+			_isInternalPositionUpdate = true;
 
-			bool removingCurrentElement = currentItemPosition == -1;
-			bool removingLastElement = e.OldStartingIndex == count;
-			bool removingFirstElement = e.OldStartingIndex == 0;
-			bool removingCurrentElementButNotFirst = removingCurrentElement && removingLastElement && ItemsView.Position > 0;
-
-			if (removingCurrentElementButNotFirst)
+			try
 			{
-				carouselPosition = ItemsView.Position - 1;
+				var carouselPosition = ItemsView.Position;
+				var currentItemPosition = GetItemPositionInCarousel(ItemsView.CurrentItem);
+				var count = (sender as IList).Count;
 
-			}
-			else if (removingFirstElement && !removingCurrentElement)
-			{
-				carouselPosition = currentItemPosition;
-			}
+				bool removingCurrentElement = currentItemPosition == -1;
+				bool removingLastElement = e.OldStartingIndex == count;
+				bool removingFirstElement = e.OldStartingIndex == 0;
+				bool removingCurrentElementButNotFirst = removingCurrentElement && removingLastElement && ItemsView.Position > 0;
 
-			// If we are adding a new item make sure to maintain the CurrentItemPosition
-			else if (e.Action == NotifyCollectionChangedAction.Add
-				&& currentItemPosition != -1)
+				if (removingCurrentElementButNotFirst)
+				{
+					carouselPosition = ItemsView.Position - 1;
+				}
+				else if (removingFirstElement && !removingCurrentElement)
+				{
+					carouselPosition = currentItemPosition;
+				}
+
+				// If we are adding a new item make sure to maintain the CurrentItemPosition
+				else if (e.Action == NotifyCollectionChangedAction.Add
+					&& currentItemPosition != -1)
+				{
+					carouselPosition = currentItemPosition;
+				}
+
+				if (ItemsView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepLastItemInView)
+				{
+					carouselPosition = count == 0 ? 0 : count - 1;
+				}
+				else if (ItemsView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepItemsInView)
+				{
+					carouselPosition = 0;
+				}
+
+				SetCarouselViewCurrentItem(carouselPosition);
+				SetCarouselViewPosition(carouselPosition);
+			}
+			finally
 			{
-				carouselPosition = currentItemPosition;
+				// Reset flag after collection operations complete
+				_isInternalPositionUpdate = false;
 			}
-
-			SetCarouselViewCurrentItem(carouselPosition);
-			SetCarouselViewPosition(carouselPosition);
 		}
 
 		void OnListViewSizeChanged(object sender, SizeChangedEventArgs e) => Resize(e.NewSize);
@@ -639,5 +681,15 @@ void InvalidateItemSize()
 				item.ItemWidth = itemWidth;
 			}
 		}
+
+		WStyle GetItemContainerStyle(bool isHorizontalLayout)
+		{
+			var h = CarouselItemsLayout?.ItemSpacing > 0 ? (CarouselItemsLayout.ItemSpacing) / 2 : 0;
+			var padding = isHorizontalLayout ? WinUIHelpers.CreateThickness(h, 0, h, 0) : WinUIHelpers.CreateThickness(0, h, 0, h);
+
+			var style = new WStyle(typeof(ListViewItem));
+			style.Setters.Add(new WSetter(Control.PaddingProperty, padding));
+			return style;
+		}
 	}
 }

src/Controls/src/Core/Handlers/Items/ItemsViewHandler.Windows.cs

@@ -148,7 +148,11 @@ void OnItemsVectorChanged(global::Windows.Foundation.Collections.IObservableVect
 					return;
 				}
 
-				var itemsCount = items.Count;
+				// When looping is enabled in CarouselView, Items. Count returns
+				// the FakeCount instead of the actual item count.
+				// Use items.Count for CollectionView to account for this
+				// behavior: otherwise, use ItemCount for other types.
+				var itemsCount = VirtualView is CollectionView ? items.Count : ItemCount;
 
 				if (itemsCount == 0)
 				{
@@ -703,7 +707,7 @@ object FindBoundItem(ScrollToRequestEventArgs args)
 			return null;
 		}
 
-		protected virtual int ItemCount => CollectionViewSource.View.Count;
+		protected virtual int ItemCount => CollectionViewSource is not null ? CollectionViewSource.View.Count : 0;
 
 		protected virtual object GetItem(int index)
 		{

src/Controls/tests/TestCases.HostApp/Issues/Issue29420.cs

@@ -0,0 +1,76 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+[Issue(IssueTracker.Github, 29420, "KeepLastInView Not Working as Expected in CarouselView", PlatformAffected.UWP)]
+public class Issue29420 : ContentPage
+{
+	public Issue29420()
+	{
+		var count = 0;
+		var verticalStackLayout = new VerticalStackLayout();
+		var carouselItems = new ObservableCollection<string>
+		{
+			"Item 0", "Item 1","Item 2", "Item 3", "Item 4", "Item 5",
+
+		};
+
+		CarouselView carouselView = new CarouselView
+		{
+			ItemsSource = carouselItems,
+			AutomationId = "CarouselView",
+			Loop = false,
+			ItemsUpdatingScrollMode = ItemsUpdatingScrollMode.KeepLastItemInView,
+
+			ItemTemplate = new DataTemplate(() =>
+			{
+				var grid = new Grid
+				{
+					Padding = 10
+				};
+
+				var label = new Label
+				{
+					VerticalOptions = LayoutOptions.Center,
+					HorizontalOptions = LayoutOptions.Center,
+					FontSize = 18,
+					Background = Colors.Pink,
+				};
+				label.SetBinding(Label.TextProperty, ".");
+				label.SetBinding(Label.AutomationIdProperty, ".");
+
+				grid.Children.Add(label);
+				return grid;
+			}),
+		};
+
+		var insertButton = new Button
+		{
+			Text = "Insert item at 0th index",
+			AutomationId = "InsertButton",
+			Margin = new Thickness(20),
+		};
+
+		var addButton = new Button
+		{
+			Text = "Add item at end",
+			AutomationId = "AddButton",
+			Margin = new Thickness(20),
+		};
+
+		insertButton.Clicked += (sender, e) =>
+		{
+			carouselItems.Insert(0, "NewItem" + count.ToString());
+			count++;
+		};
+
+		addButton.Clicked += (sender, e) =>
+		{
+			carouselItems.Add("NewItem");
+		};
+
+		verticalStackLayout.Children.Add(insertButton);
+		verticalStackLayout.Children.Add(addButton);
+		verticalStackLayout.Children.Add(carouselView);
+		Content = verticalStackLayout;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue29420.cs

@@ -0,0 +1,34 @@
+#if TEST_FAILS_ON_ANDROID && TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST // CarouselView Fails to Keep Last Item in View on iOS, android and macOS https://github.com/dotnet/maui/issues/18029, https://github.com/dotnet/maui/issues/29415
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+public class Issue29420 : _IssuesUITest
+{
+	public override string Issue => "KeepLastInView Not Working as Expected in CarouselView";
+
+	public Issue29420(TestDevice device) : base(device)
+	{ }
+
+	[Test, Order(1)]
+	[Category(UITestCategories.CarouselView)]
+	public async Task VerifyCarouselViewKeepLastInViewOnItemInsert()
+	{
+		App.WaitForElement("CarouselView");
+		App.Tap("InsertButton");
+		await Task.Delay(200); // Wait for the scrollbar to disappear.
+		VerifyScreenshot("CarouselViewKeepLastInViewOnItemInsert");
+	}
+
+	[Test, Order(2)]
+	[Category(UITestCategories.CarouselView)]
+	public async Task VerifyCarouselViewKeepLastInViewOnItemAdd()
+	{
+		App.WaitForElement("CarouselView");
+		App.Tap("AddButton");
+		await Task.Delay(200); // Wait for the scrollbar to disappear.
+		VerifyScreenshot("CarouselViewKeepLastInViewOnItemAdd");
+	}
+}
+#endif