Revert "Prevent iOS CollectionView size shifts from clearing the cell…

… size cache (#18464)"

This reverts commit 6a5bbf0.

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

@@ -7,6 +7,7 @@
 using Foundation;
 using Microsoft.Maui.Controls.Internals;
 using Microsoft.Maui.Graphics;
+using ObjCRuntime;
 using UIKit;
 
 namespace Microsoft.Maui.Controls.Handlers.Items
@@ -177,12 +178,12 @@ public override void ViewDidLoad()
 		public override void ViewWillAppear(bool animated)
 		{
 			base.ViewWillAppear(animated);
-			ConstrainItemsToBounds();
+			ConstrainToItemsView();
 		}
 
 		public override void ViewWillLayoutSubviews()
 		{
-			ConstrainItemsToBounds();
+			ConstrainToItemsView();
 			base.ViewWillLayoutSubviews();
 			InvalidateMeasureIfContentSizeChanged();
 			LayoutEmptyView();
@@ -242,19 +243,26 @@ void InvalidateMeasureIfContentSizeChanged()
 
 		internal Size? GetSize()
 		{
-			if (_emptyViewDisplayed) 
+			if (_emptyViewDisplayed)
 			{
 				return _emptyUIView.Frame.Size.ToSize();
 			}
 
 			return CollectionView.CollectionViewLayout.CollectionViewContentSize.ToSize();
 		}
 
-		void ConstrainItemsToBounds()
+		void ConstrainToItemsView()
 		{
-			var contentBounds = CollectionView.AdjustedContentInset.InsetRect(CollectionView.Bounds);
-			var constrainedSize = contentBounds.Size;
-			ItemsViewLayout.UpdateConstraints(constrainedSize);
+			var itemsViewWidth = ItemsView.Width;
+			var itemsViewHeight = ItemsView.Height;
+
+			if (itemsViewHeight < 0 || itemsViewWidth < 0)
+			{
+				ItemsViewLayout.UpdateConstraints(CollectionView.Bounds.Size);
+				return;
+			}
+
+			ItemsViewLayout.UpdateConstraints(new CGSize(itemsViewWidth, itemsViewHeight));
 		}
 
 		void EnsureLayoutInitialized()
@@ -313,6 +321,7 @@ public virtual void UpdateFlowDirection()
 			Layout.InvalidateLayout();
 		}
 
+
 		public override nint NumberOfSections(UICollectionView collectionView)
 		{
 			CheckForEmptySource();

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

@@ -5,6 +5,8 @@
 using CoreGraphics;
 using Foundation;
 using Microsoft.Extensions.Logging;
+using Microsoft.Maui.Controls.Internals;
+using ObjCRuntime;
 using UIKit;
 
 namespace Microsoft.Maui.Controls.Handlers.Items
@@ -19,7 +21,9 @@ public abstract class ItemsViewLayout : UICollectionViewFlowLayout
 		CGSize _currentSize;
 		WeakReference<Func<UICollectionViewCell>> _getPrototype;
 
-		readonly Dictionary<object, CGSize> _cellSizeCache = new();
+		const double ConstraintSizeTolerance = 0.00001;
+
+		Dictionary<object, CGSize> _cellSizeCache = new Dictionary<object, CGSize>();
 
 		public ItemsUpdatingScrollMode ItemsUpdatingScrollMode { get; set; }
 
@@ -98,7 +102,7 @@ protected virtual void HandlePropertyChanged(PropertyChangedEventArgs propertyCh
 
 		internal virtual void UpdateConstraints(CGSize size)
 		{
-			if (size.IsCloseTo(_currentSize))
+			if (!RequiresConstraintUpdate(size, _currentSize))
 			{
 				return;
 			}
@@ -564,12 +568,23 @@ static void ForceScrollToLastItem(UICollectionView collectionView, ItemsLayout i
 
 		public override bool ShouldInvalidateLayoutForBoundsChange(CGRect newBounds)
 		{
-			if(newBounds.Size == _currentSize)
+			if (newBounds.Size == _currentSize)
 			{
 				return base.ShouldInvalidateLayoutForBoundsChange(newBounds);
 			}
 
-			UpdateConstraints(CollectionView.AdjustedContentInset.InsetRect(newBounds).Size);
+			if (OperatingSystem.IsIOSVersionAtLeast(11) || OperatingSystem.IsMacCatalystVersionAtLeast(11)
+#if TVOS
+				|| OperatingSystem.IsTvOSVersionAtLeast(11)
+#endif
+			)
+			{
+				UpdateConstraints(CollectionView.AdjustedContentInset.InsetRect(newBounds).Size);
+			}
+			else
+			{
+				UpdateConstraints(CollectionView.Bounds.Size);
+			}
 
 			return true;
 		}
@@ -595,5 +610,20 @@ internal void ClearCellSizeCache()
 		{
 			_cellSizeCache.Clear();
 		}
+
+		bool RequiresConstraintUpdate(CGSize newSize, CGSize current)
+		{
+			if (Math.Abs(newSize.Width - current.Width) > ConstraintSizeTolerance)
+			{
+				return true;
+			}
+
+			if (Math.Abs(newSize.Height - current.Height) > ConstraintSizeTolerance)
+			{
+				return true;
+			}
+
+			return false;
+		}
 	}
 }

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

@@ -5,6 +5,7 @@
 using Foundation;
 using Microsoft.Maui.Controls.Internals;
 using Microsoft.Maui.Graphics;
+using ObjCRuntime;
 using UIKit;
 
 namespace Microsoft.Maui.Controls.Handlers.Items
@@ -65,7 +66,7 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
 
 			var preferredSize = preferredAttributes.Frame.Size;
 
-			if (preferredSize.IsCloseTo(_size)
+			if (SizesAreSame(preferredSize, _size)
 				&& AttributesConsistentWithConstrainedDimension(preferredAttributes))
 			{
 				return preferredAttributes;
@@ -78,6 +79,8 @@ public override UICollectionViewLayoutAttributes PreferredLayoutAttributesFittin
 
 			OnLayoutAttributesChanged(preferredAttributes);
 
+			//_isMeasured = true;
+
 			return preferredAttributes;
 		}
 
@@ -287,6 +290,23 @@ protected void OnLayoutAttributesChanged(UICollectionViewLayoutAttributes newAtt
 
 		protected abstract bool AttributesConsistentWithConstrainedDimension(UICollectionViewLayoutAttributes attributes);
 
+		bool SizesAreSame(CGSize preferredSize, Size elementSize)
+		{
+			const double tolerance = 0.000001;
+
+			if (Math.Abs(preferredSize.Height - elementSize.Height) > tolerance)
+			{
+				return false;
+			}
+
+			if (Math.Abs(preferredSize.Width - elementSize.Width) > tolerance)
+			{
+				return false;
+			}
+
+			return true;
+		}
+
 		void UpdateVisualStates()
 		{
 			if (PlatformHandler?.VirtualView is VisualElement element)

src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.cs

@@ -34,10 +34,6 @@ void SetupBuilder()
 					handlers.AddHandler<VerticalStackLayout, LayoutHandler>();
 					handlers.AddHandler<Grid, LayoutHandler>();
 					handlers.AddHandler<Label, LabelHandler>();
-
-#if IOS && !MACCATALYST
-					handlers.AddHandler<CacheTestCollectionView, CacheTestCollectionViewHandler>();
-#endif
 				});
 			});
 		}