Fix CarouselView layout SR6 regressions

src/Controls/src/Core/Handlers/Items/iOS/CarouselTemplatedCell.cs

@@ -32,7 +32,10 @@ public override void ConstrainTo(CGSize constraint)
 
 		public override CGSize Measure()
 		{
-			return new CGSize(_constraint.Width, _constraint.Height);
+			// Go through the measure pass even if the constraints are fixed
+			// to ensure arrange pass has the appropriate desired size in place.
+			PlatformHandler.VirtualView.Measure(_constraint.Width, _constraint.Height);
+			return _constraint;
 		}
 
 		protected override (bool, Size) NeedsContentSizeUpdate(Size currentSize)
@@ -42,7 +45,7 @@ protected override (bool, Size) NeedsContentSizeUpdate(Size currentSize)
 
 		protected override bool AttributesConsistentWithConstrainedDimension(UICollectionViewLayoutAttributes attributes)
 		{
-			return false;
+			return _constraint.IsCloseTo(attributes.Frame.Size);
 		}
 	}
 }

src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs

@@ -199,6 +199,9 @@ protected override string DetermineCellReuseId(NSIndexPath indexPath)
 			return base.DetermineCellReuseId(NSIndexPath.FromItemSection(itemIndex, 0));
 		}
 
+		private protected override (Type CellType, string CellTypeReuseId) DetermineTemplatedCellType()
+			=> (typeof(CarouselTemplatedCell), "maui_carousel");
+
 		protected override void RegisterViewTypes()
 		{
 			CollectionView.RegisterClassForCell(typeof(CarouselTemplatedCell), CarouselTemplatedCell.ReuseId);

src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs

@@ -503,9 +503,9 @@ protected virtual string DetermineCellReuseId(NSIndexPath indexPath)
 				var dataTemplate = ItemsView.ItemTemplate.SelectDataTemplate(item, ItemsView);
 
 				var cellOrientation = ItemsViewLayout.ScrollDirection == UICollectionViewScrollDirection.Vertical ? "v" : "h";
-				var cellType = ItemsViewLayout.ScrollDirection == UICollectionViewScrollDirection.Vertical ? typeof(VerticalCell) : typeof(HorizontalCell);
+				(Type cellType, var cellTypeReuseId) = DetermineTemplatedCellType();
 
-				var reuseId = $"_maui_{cellOrientation}_{dataTemplate.Id}";
+				var reuseId = $"_{cellTypeReuseId}_{cellOrientation}_{dataTemplate.Id}";
 
 				if (!_cellReuseIds.Contains(reuseId))
 				{
@@ -521,6 +521,11 @@ protected virtual string DetermineCellReuseId(NSIndexPath indexPath)
 				: VerticalDefaultCell.ReuseId;
 		}
 
+		private protected virtual (Type CellType, string CellTypeReuseId) DetermineTemplatedCellType()
+		{
+			return (ItemsViewLayout.ScrollDirection == UICollectionViewScrollDirection.Vertical ? typeof(VerticalCell) : typeof(HorizontalCell), "maui");
+		}
+
 		[Obsolete("Use DetermineCellReuseId(NSIndexPath indexPath) instead.")]
 		protected virtual string DetermineCellReuseId()
 		{

src/Controls/src/Core/Handlers/Items2/CarouselViewHandler2.iOS.cs

@@ -38,8 +38,7 @@ protected override CarouselViewController2 CreateController(CarouselView newElem
 
 		protected override UICollectionViewLayout SelectLayout()
 		{
-			bool IsHorizontal = VirtualView.ItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal;
-			UICollectionViewScrollDirection scrollDirection = IsHorizontal ? UICollectionViewScrollDirection.Horizontal : UICollectionViewScrollDirection.Vertical;
+			bool isHorizontal = VirtualView.ItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal;
 
 			NSCollectionLayoutDimension itemWidth = NSCollectionLayoutDimension.CreateFractionalWidth(1);
 			NSCollectionLayoutDimension itemHeight = NSCollectionLayoutDimension.CreateFractionalHeight(1);
@@ -55,7 +54,7 @@ protected override UICollectionViewLayout SelectLayout()
 					return null;
 				}
 				double sectionMargin = 0.0;
-				if (!IsHorizontal)
+				if (!isHorizontal)
 				{
 					sectionMargin = VirtualView.PeekAreaInsets.VerticalThickness / 2;
 					var newGroupHeight = environment.Container.ContentSize.Height - VirtualView.PeekAreaInsets.VerticalThickness;
@@ -81,19 +80,19 @@ protected override UICollectionViewLayout SelectLayout()
 
 				if (OperatingSystem.IsIOSVersionAtLeast(16))
 				{
-					group = IsHorizontal ? NSCollectionLayoutGroup.GetHorizontalGroup(groupSize, item, 1) :
+					group = isHorizontal ? NSCollectionLayoutGroup.GetHorizontalGroup(groupSize, item, 1) :
 										   NSCollectionLayoutGroup.GetVerticalGroup(groupSize, item, 1);
 				}
 				else
 				{
-					group = IsHorizontal ? NSCollectionLayoutGroup.CreateHorizontal(groupSize, item, 1) :
+					group = isHorizontal ? NSCollectionLayoutGroup.CreateHorizontal(groupSize, item, 1) :
 										   NSCollectionLayoutGroup.CreateVertical(groupSize, item, 1);
 				}
 
 				// Create our section layout
 				var section = NSCollectionLayoutSection.Create(group: group);
 				section.InterGroupSpacing = itemSpacing;
-				section.OrthogonalScrollingBehavior = IsHorizontal ? UICollectionLayoutSectionOrthogonalScrollingBehavior.GroupPagingCentered : UICollectionLayoutSectionOrthogonalScrollingBehavior.None;
+				section.OrthogonalScrollingBehavior = isHorizontal ? UICollectionLayoutSectionOrthogonalScrollingBehavior.GroupPagingCentered : UICollectionLayoutSectionOrthogonalScrollingBehavior.None;
 				section.VisibleItemsInvalidationHandler = (items, offset, env) =>
 				{
 					//This will allow us to SetPosition when we are scrolling the items

src/Controls/src/Core/Handlers/Items2/iOS/CarouselTemplatedCell2.cs

@@ -0,0 +1,22 @@
+#nullable disable
+using CoreGraphics;
+using Foundation;
+using Microsoft.Maui.Graphics;
+using UIKit;
+
+namespace Microsoft.Maui.Controls.Handlers.Items2
+{
+	internal sealed class CarouselTemplatedCell2 : TemplatedCell2
+	{
+		internal new const string ReuseId = "Microsoft.Maui.Controls.CarouselTemplatedCell2";
+
+		[Export("initWithFrame:")]
+		[Microsoft.Maui.Controls.Internals.Preserve(Conditional = true)]
+		public CarouselTemplatedCell2(CGRect frame) : base(frame)
+		{
+		}
+
+		private protected override Size GetMeasureConstraints(UICollectionViewLayoutAttributes preferredAttributes)
+			=> preferredAttributes.Size.ToSize();
+	}
+}

src/Controls/src/Core/Handlers/Items2/iOS/CarouselViewController2.cs

@@ -117,6 +117,9 @@ protected override string DetermineCellReuseId(NSIndexPath indexPath)
 			return base.DetermineCellReuseId(itemIndex);
 		}
 
+		private protected override (Type CellType, string CellTypeReuseId) DetermineTemplatedCellType()
+			=> (typeof(CarouselTemplatedCell2), CarouselTemplatedCell2.ReuseId);
+
 		protected override Items.IItemsViewSource CreateItemsViewSource()
 		{
 			var itemsSource = ItemsSourceFactory2.CreateForCarouselView(ItemsView.ItemsSource, this, ItemsView.Loop);
@@ -506,54 +509,49 @@ async Task UpdateInitialPosition()
 				return;
 			}
 
-			int position = carousel.Position;
-			var currentItem = carousel.CurrentItem;
-
-			if (currentItem != null)
-			{
-				// Sometimes the item could be just being removed while we navigate back to the CarouselView
-				var positionCurrentItem = ItemsSource.GetIndexForItem(currentItem).Row;
-				if (positionCurrentItem != -1)
-				{
-					position = positionCurrentItem;
-				}
-			}
-
-			var projectedPosition = NSIndexPath.FromItemSection(position, _section);
-
-			if (LoopItemsSource.Loop)
-			{
-				//We need to set the position to the correct position since we added 1 item at the beginning
-				projectedPosition = GetScrollToIndexPath(position);
-			}
-
-			var uICollectionViewScrollPosition = IsHorizontal ? UICollectionViewScrollPosition.CenteredHorizontally : UICollectionViewScrollPosition.CenteredVertically;
-
-			await Task.Delay(100).ContinueWith((t) =>
+			await Task.Delay(100).ContinueWith(_ =>
 			{
 				MainThread.BeginInvokeOnMainThread(() =>
 				{
 					if (!IsViewLoaded)
 					{
 						return;
 					}
+
 					InitialPositionSet = true;
 
 					if (ItemsSource is null || ItemsSource.ItemCount == 0)
 					{
 						return;
 					}
 
+					int position = carousel.Position;
+					var currentItem = carousel.CurrentItem;
+
+					if (currentItem != null)
+					{
+						// Sometimes the item could be just being removed while we navigate back to the CarouselView
+						var positionCurrentItem = ItemsSource.GetIndexForItem(currentItem).Row;
+						if (positionCurrentItem != -1)
+						{
+							position = positionCurrentItem;
+						}
+					}
+
+					var projectedPosition = LoopItemsSource.Loop
+						? GetScrollToIndexPath(position) // We need to set the position to the correct position since we added 1 item at the beginning
+						: NSIndexPath.FromItemSection(position, _section);
+
+					var uICollectionViewScrollPosition = IsHorizontal ? UICollectionViewScrollPosition.CenteredHorizontally : UICollectionViewScrollPosition.CenteredVertically;
+
 					CollectionView.ScrollToItem(projectedPosition, uICollectionViewScrollPosition, false);
 
 					//Set the position on VirtualView to update the CurrentItem also
 					SetPosition(position);
 
 					UpdateVisualStates();
 				});
-
 			});
-
 		}
 
 		void UpdateVisualStates()

src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs

@@ -61,6 +61,9 @@ public void UpdateLayout(UICollectionViewLayout newLayout)
 
 			if (newLayout is UICollectionViewCompositionalLayout compositionalLayout)
 			{
+				// Note: on carousel layout, the scroll direction is always vertical to achieve horizontal paging with snapping.
+				// Thanks to it, we can use OrthogonalScrollingBehavior.GroupPagingCentered to scroll the section horizontally.
+				// And even if CarouselView is vertically oriented, each section scrolls horizontally — which results in the carousel-style behavior.
 				ScrollDirection = compositionalLayout.Configuration.ScrollDirection;
 			}
 
@@ -330,10 +333,9 @@ protected virtual string DetermineCellReuseId(NSIndexPath indexPath)
 
 				var dataTemplate = ItemsView.ItemTemplate.SelectDataTemplate(item, ItemsView);
 
-				var cellType = typeof(TemplatedCell2);
-
 				var orientation = ScrollDirection == UICollectionViewScrollDirection.Horizontal ? "Horizontal" : "Vertical";
-				var reuseId = $"{TemplatedCell2.ReuseId}.{orientation}.{dataTemplate.Id}";
+				(Type cellType, var cellTypeReuseId) = DetermineTemplatedCellType();
+				var reuseId = $"{cellTypeReuseId}.{orientation}.{dataTemplate.Id}";
 
 				if (!_cellReuseIds.Contains(reuseId))
 				{
@@ -347,6 +349,9 @@ protected virtual string DetermineCellReuseId(NSIndexPath indexPath)
 			return ScrollDirection == UICollectionViewScrollDirection.Horizontal ? HorizontalDefaultCell2.ReuseId : VerticalDefaultCell2.ReuseId;
 		}
 
+		private protected virtual (Type CellType, string CellTypeReuseId) DetermineTemplatedCellType()
+			=> (typeof(TemplatedCell2), TemplatedCell2.ReuseId);
+
 		protected virtual void RegisterViewTypes()
 		{
 			CollectionView.RegisterClassForCell(typeof(HorizontalDefaultCell2), HorizontalDefaultCell2.ReuseId);

src/Controls/src/Core/Handlers/Items2/iOS/TemplatedCell2.cs

@@ -86,9 +86,7 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
 
 			if (PlatformHandler?.VirtualView is { } virtualView)
 			{
-				var constraints = ScrollDirection == UICollectionViewScrollDirection.Vertical
-					? new Size(preferredAttributes.Size.Width, double.PositiveInfinity)
-					: new Size(double.PositiveInfinity, preferredAttributes.Size.Height);
+				var constraints = GetMeasureConstraints(preferredAttributes);
 
 				if (_measureInvalidated || _cachedConstraints != constraints)
 				{
@@ -98,9 +96,12 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
 					_needsArrange = true;
 				}
 
-				var size = ScrollDirection == UICollectionViewScrollDirection.Vertical
-					? new Size(preferredAttributes.Size.Width, _measuredSize.Height)
-					: new Size(_measuredSize.Width, preferredAttributes.Size.Height);
+				var preferredSize = preferredAttributes.Size;
+				// Use measured size only when unconstrained
+				var size = new Size(
+					double.IsPositiveInfinity(constraints.Width) ? _measuredSize.Width : preferredSize.Width,
+					double.IsPositiveInfinity(constraints.Height) ? _measuredSize.Height : preferredSize.Height
+				);
 
 				preferredAttributes.Frame = new CGRect(preferredAttributes.Frame.Location, size);
 				preferredAttributes.ZIndex = 2;
@@ -111,6 +112,14 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
 			return preferredAttributes;
 		}
 
+		private protected virtual Size GetMeasureConstraints(UICollectionViewLayoutAttributes preferredAttributes)
+		{
+			var constraints = ScrollDirection == UICollectionViewScrollDirection.Vertical
+				? new Size(preferredAttributes.Size.Width, double.PositiveInfinity)
+				: new Size(double.PositiveInfinity, preferredAttributes.Size.Height);
+			return constraints;
+		}
+
 		public override void LayoutSubviews()
 		{
 			base.LayoutSubviews();

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

@@ -100,8 +100,6 @@ void ExecuteRemoveItemsCommand()
 			while (Items.Count > 0)
 			{
 				Items.Remove(Items.Last());
-				Items.Remove(Items.Last());
-				Items.Remove(Items.Last());
 			}
 			RemoveAllItemsCommand.ChangeCanExecute();
 			RemoveLastItemCommand.ChangeCanExecute();