[Android, Windows] Fix CarouselView PreviousPosition/PreviousItem incorrect during animated ScrollTo()

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

@@ -185,6 +185,7 @@ public override void ScrollTo(ScrollToRequestEventArgs args)
 			// And at the same time the user is requesting we go to a particular item
 			if (position == -1)
 			{
+				_gotoPosition = -1;
 				if (Carousel.Loop)
 					_carouselViewLoopManager.AddPendingScrollTo(args);
 
@@ -193,6 +194,8 @@ public override void ScrollTo(ScrollToRequestEventArgs args)
 
 			if (args.IsAnimated)
 			{
+				if (_gotoPosition == -1)
+					_gotoPosition = args.Index;
 				ScrollHelper.AnimateScrollToPosition(position, args.ScrollToPosition);
 			}
 			else
@@ -506,8 +509,6 @@ void IMauiCarouselRecyclerView.UpdateFromCurrentItem()
 				_gotoPosition = currentItemPosition;
 				ItemsView.ScrollTo(currentItemPosition, position: Microsoft.Maui.Controls.ScrollToPosition.Center, animate: Carousel.AnimateCurrentItemChanges);
 			}
-
-			_gotoPosition = -1;
 		}
 
 		void IMauiCarouselRecyclerView.UpdateFromPosition()

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

@@ -3,6 +3,7 @@
 using System.Collections;
 using System.Collections.Specialized;
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.Maui.Controls.Platform;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
@@ -25,6 +26,7 @@ public partial class CarouselViewHandler : ItemsViewHandler<CarouselView>
 		WScrollBarVisibility? _verticalScrollBarVisibilityWithoutLoop;
 		Size _currentSize;
 		bool _isCarouselViewReady;
+		int _gotoPosition = -1;
 		NotifyCollectionChangedEventHandler _collectionChanged;
 		readonly WeakNotifyCollectionChangedProxy _proxy = new();
 
@@ -190,6 +192,28 @@ public static void MapCurrentItem(CarouselViewHandler handler, CarouselView caro
 			handler.UpdateCurrentItem();
 		}
 
+		protected override async Task ScrollTo(ScrollToRequestEventArgs args)
+		{
+			if (args.IsAnimated && args.Mode == ScrollToMode.Position)
+			{
+				_gotoPosition = args.Index;
+
+				// Commit position before animation so PreviousPosition/PreviousItem are correct immediately.
+				SetCarouselViewPosition(_gotoPosition);
+			}
+
+			try
+			{
+				await base.ScrollTo(args);
+			}
+			finally
+			{
+				// Conditional reset guards against a concurrent ScrollTo replacing the target.
+				if (_gotoPosition == args.Index)
+					_gotoPosition = -1;
+			}
+		}
+
 		public static void MapPosition(CarouselViewHandler handler, CarouselView carouselView)
 		{
 			// If the initial position hasn't been set, we have a UpdateInitialPosition call on CarouselViewHandler
@@ -385,7 +409,14 @@ void UpdateCurrentItem()
 			var currentItemPosition = GetItemPositionInCarousel(ItemsView.CurrentItem);
 
 			if (currentItemPosition < 0 || currentItemPosition >= ItemCount)
+			{
 				return;
+			}
+
+			if (_gotoPosition != -1)
+			{
+				return;
+			}
 
 			ItemsView.ScrollTo(currentItemPosition, position: ScrollToPosition.Center, animate: ItemsView.AnimateCurrentItemChanges);
 		}
@@ -491,6 +522,12 @@ void UpdateScrollBarVisibilityForLoop()
 
 		void CarouselScrolled(object sender, ItemsViewScrolledEventArgs e)
 		{
+			// Ignore ViewChanged events fired before the initial position is established.
+			if (!InitialPositionSet)
+			{
+				return;
+			}
+
 			var position = e.CenterItemIndex;
 
 			if (position == -1)
@@ -503,6 +540,12 @@ void CarouselScrolled(object sender, ItemsViewScrolledEventArgs e)
 				return;
 			}
 
+			// Suppress intermediate scroll events during a programmatic animated scroll.
+			if (_gotoPosition != -1)
+			{
+				return;
+			}
+
 			SetCarouselViewPosition(position);
 		}
 

src/Controls/src/Core/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -1,2 +1,3 @@
 #nullable enable
+~override Microsoft.Maui.Controls.Handlers.Items.CarouselViewHandler.ScrollTo(Microsoft.Maui.Controls.ScrollToRequestEventArgs args) -> System.Threading.Tasks.Task
 override Microsoft.Maui.Controls.Shapes.Shape.OnPropertyChanged(string? propertyName = null) -> void

src/Controls/tests/TestCases.HostApp/Issues/Issue29544.cs

@@ -0,0 +1,152 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 29544,
+	"PreviousItem and PreviousPosition not updating correctly on ScrollTo or Position set",
+	PlatformAffected.Android | PlatformAffected.UWP)]
+public class Issue29544 : ContentPage
+{
+	readonly CarouselView _carouselView;
+	readonly ObservableCollection<string> _items;
+	readonly Label _previousItemLabel;
+	readonly Label _previousPositionLabel;
+	readonly Label _currentItemLabel;
+	readonly Label _currentPositionLabel;
+
+	public Issue29544()
+	{
+		_items = new ObservableCollection<string>
+		{
+			"Item 1",
+			"Item 2",
+			"Item 3",
+			"Item 4",
+			"Item 5"
+		};
+
+		_currentItemLabel = new Label
+		{
+			AutomationId = "CurrentItemLabel",
+			Text = "Current Item: Item 1"
+		};
+
+		_previousItemLabel = new Label
+		{
+			AutomationId = "PreviousItemLabel",
+			Text = "Previous Item: none"
+		};
+
+		_currentPositionLabel = new Label
+		{
+			AutomationId = "CurrentPositionLabel",
+			Text = "Current Position: 0"
+		};
+
+		_previousPositionLabel = new Label
+		{
+			AutomationId = "PreviousPositionLabel",
+			Text = "Previous Position: none"
+		};
+
+		_carouselView = new CarouselView
+		{
+			AutomationId = "CarouselView",
+			Loop = false,
+			ItemsSource = _items,
+			ItemTemplate = new DataTemplate(() =>
+			{
+				var label = new Label
+				{
+					FontSize = 24,
+					BackgroundColor = Colors.LightGray,
+					HorizontalOptions = LayoutOptions.Fill,
+					VerticalOptions = LayoutOptions.Center,
+					HorizontalTextAlignment = TextAlignment.Center
+				};
+				label.SetBinding(Label.TextProperty, ".");
+				return label;
+			})
+		};
+
+		_carouselView.CurrentItemChanged += OnCurrentItemChanged;
+		_carouselView.PositionChanged += OnPositionChanged;
+
+		var scrollTo3Button = new Button
+		{
+			AutomationId = "ScrollTo3Button",
+			Text = "Scroll To 3"
+		};
+		scrollTo3Button.Clicked += (s, e) => _carouselView.ScrollTo(3);
+
+		var scrollTo1Button = new Button
+		{
+			AutomationId = "ScrollTo1Button",
+			Text = "Scroll To 1"
+		};
+		scrollTo1Button.Clicked += (s, e) => _carouselView.ScrollTo(1);
+
+		var setPosition3Button = new Button
+		{
+			AutomationId = "SetPosition3Button",
+			Text = "Set Position 3"
+		};
+		setPosition3Button.Clicked += (s, e) => _carouselView.Position = 3;
+
+		var setPosition0Button = new Button
+		{
+			AutomationId = "SetPosition0Button",
+			Text = "Set Position 0"
+		};
+		setPosition0Button.Clicked += (s, e) => _carouselView.Position = 0;
+
+		Content = new Grid
+		{
+			Padding = new Thickness(10),
+			RowDefinitions =
+			{
+				new RowDefinition { Height = GridLength.Auto },
+				new RowDefinition { Height = GridLength.Star }
+			},
+			Children =
+			{
+				new VerticalStackLayout
+				{
+					Spacing = 6,
+					Children =
+					{
+						_currentItemLabel,
+						_previousItemLabel,
+						_currentPositionLabel,
+						_previousPositionLabel,
+						new HorizontalStackLayout
+						{
+							Spacing = 8,
+							Children = { scrollTo3Button, scrollTo1Button }
+						},
+						new HorizontalStackLayout
+						{
+							Spacing = 8,
+							Children = { setPosition3Button, setPosition0Button }
+						}
+					}
+				},
+				_carouselView
+			}
+		};
+
+		Grid.SetRow(_carouselView, 1);
+	}
+
+	void OnCurrentItemChanged(object sender, CurrentItemChangedEventArgs e)
+	{
+		_currentItemLabel.Text = $"Current Item: {e.CurrentItem}";
+		_previousItemLabel.Text = $"Previous Item: {e.PreviousItem ?? "none"}";
+	}
+
+	void OnPositionChanged(object sender, PositionChangedEventArgs e)
+	{
+		_currentPositionLabel.Text = $"Current Position: {e.CurrentPosition}";
+		_previousPositionLabel.Text = $"Previous Position: {e.PreviousPosition}";
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue29544.cs

@@ -0,0 +1,84 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue29544 : _IssuesUITest
+{
+	public override string Issue =>
+		"PreviousItem and PreviousPosition not updating correctly on ScrollTo or Position set";
+
+	public Issue29544(TestDevice device) : base(device) { }
+
+	[Test]
+	[Category(UITestCategories.CarouselView)]
+	public void PreviousPositionUpdatesCorrectlyOnScrollTo()
+	{
+		App.WaitForElement("ScrollTo3Button");
+		App.Tap("ScrollTo3Button");
+
+		App.RetryAssert(() =>
+		{
+			var currentPos = App.FindElement("CurrentPositionLabel").GetText();
+			Assert.That(currentPos, Does.Contain("3"),
+				"CarouselView should reach position 3 after ScrollTo");
+		});
+
+		var previousPositionText = App.FindElement("PreviousPositionLabel").GetText();
+		Assert.That(previousPositionText, Does.Contain("0"),
+			"After scrolling from position 0 to 3, PreviousPosition should be 0");
+
+		var previousItemText = App.FindElement("PreviousItemLabel").GetText();
+		Assert.That(previousItemText, Does.Contain("Item 1"),
+			"After scrolling from position 0 to 3, PreviousItem should be 'Item 1'");
+
+		App.Tap("ScrollTo1Button");
+
+		App.RetryAssert(() =>
+		{
+			var currentPos = App.FindElement("CurrentPositionLabel").GetText();
+			Assert.That(currentPos, Does.Contain("1"),
+				"CarouselView should reach position 1 after second ScrollTo");
+		});
+
+		var secondPreviousPosition = App.FindElement("PreviousPositionLabel").GetText();
+		Assert.That(secondPreviousPosition, Does.Contain("3"),
+			"After scrolling from position 3 to 1, PreviousPosition should be 3");
+
+		var secondPreviousItem = App.FindElement("PreviousItemLabel").GetText();
+		Assert.That(secondPreviousItem, Does.Contain("Item 4"),
+			"After scrolling from position 3 to 1, PreviousItem should be 'Item 4'");
+	}
+
+	[Test]
+	[Category(UITestCategories.CarouselView)]
+	public void PreviousPositionUpdatesCorrectlyOnSetPosition()
+	{
+		App.WaitForElement("SetPosition0Button");
+		App.Tap("SetPosition0Button");
+
+		App.RetryAssert(() =>
+		{
+			var pos = App.FindElement("CurrentPositionLabel").GetText();
+			Assert.That(pos, Does.Contain("0"), "CarouselView should be at position 0");
+		});
+
+		App.Tap("SetPosition3Button");
+
+		App.RetryAssert(() =>
+		{
+			var currentPos = App.FindElement("CurrentPositionLabel").GetText();
+			Assert.That(currentPos, Does.Contain("3"),
+				"CarouselView should reach position 3 after setting Position = 3");
+		});
+
+		var previousPositionText = App.FindElement("PreviousPositionLabel").GetText();
+		Assert.That(previousPositionText, Does.Contain("0"),
+			"After setting Position from 0 to 3, PreviousPosition should be 0");
+
+		var previousItemText = App.FindElement("PreviousItemLabel").GetText();
+		Assert.That(previousItemText, Does.Contain("Item 1"),
+			"After setting Position from 0 to 3, PreviousItem should be 'Item 1'");
+	}
+}