Fix iOS CollectionView not reacting properly to orientation changes

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

@@ -24,9 +24,13 @@ protected ItemsViewCell(CGRect frame) : base(frame)
 		}
 
 		protected void InitializeContentConstraints(UIView platformView)
+		{
+			SetupPlatformView(platformView, true);
+		}
+
+		private protected void SetupPlatformView(UIView platformView, bool autoLayout = false)
 		{
 			ContentView.TranslatesAutoresizingMaskIntoConstraints = false;
-			platformView.TranslatesAutoresizingMaskIntoConstraints = false;
 
 			ContentView.AddSubview(platformView);
 
@@ -36,12 +40,15 @@ protected void InitializeContentConstraints(UIView platformView)
 			ContentView.LeadingAnchor.ConstraintEqualTo(LeadingAnchor).Active = true;
 			ContentView.TrailingAnchor.ConstraintEqualTo(TrailingAnchor).Active = true;
 
-			// And we want the ContentView to be the same size as the root renderer for the Forms element
-			// TODO: we should probably remove this to support `Margin` applied to the cell's root `VirtualView`
-			ContentView.TopAnchor.ConstraintEqualTo(platformView.TopAnchor).Active = true;
-			ContentView.BottomAnchor.ConstraintEqualTo(platformView.BottomAnchor).Active = true;
-			ContentView.LeadingAnchor.ConstraintEqualTo(platformView.LeadingAnchor).Active = true;
-			ContentView.TrailingAnchor.ConstraintEqualTo(platformView.TrailingAnchor).Active = true;
+			if (autoLayout)
+			{
+				// And we want the ContentView to be the same size as the root renderer for the Forms element
+				platformView.TranslatesAutoresizingMaskIntoConstraints = false;
+				ContentView.TopAnchor.ConstraintEqualTo(platformView.TopAnchor).Active = true;
+				ContentView.BottomAnchor.ConstraintEqualTo(platformView.BottomAnchor).Active = true;
+				ContentView.LeadingAnchor.ConstraintEqualTo(platformView.LeadingAnchor).Active = true;
+				ContentView.TrailingAnchor.ConstraintEqualTo(platformView.TrailingAnchor).Active = true;
+			}
 		}
 
 		public abstract void ConstrainTo(nfloat constant);

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

@@ -1,8 +1,8 @@
 #nullable disable
 using System;
 using System.Collections.Generic;
-using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using CoreGraphics;
 using Foundation;
 using Microsoft.Maui.Controls.Internals;
@@ -200,19 +200,42 @@ public override void ViewWillLayoutSubviews()
 		{
 			ConstrainItemsToBounds();
 
-			if (CollectionView is Items.MauiCollectionView { NeedsCellLayout: true } collectionView)
+			var mauiCollectionView = CollectionView as MauiCollectionView;
+			var needsCellLayout = mauiCollectionView?.NeedsCellLayout is true;
+			if (needsCellLayout)
 			{
 				InvalidateLayoutIfItemsMeasureChanged();
-				collectionView.NeedsCellLayout = false;
+				mauiCollectionView.NeedsCellLayout = false;
 			}
 
 			base.ViewWillLayoutSubviews();
+
+			if (needsCellLayout || !_laidOut)
+			{
+				// We don't want to mess up with ContentOffset while refreshing, given that's also gonna cause
+				// a change in the content's offset Y.
+				if (!IsRefreshing())
+				{
+					MeasureSupplementaryViews();
+					LayoutSupplementaryViews();
+				}
+			}
+
 			InvalidateMeasureIfContentSizeChanged();
-			LayoutEmptyView();
 
 			_laidOut = true;
 		}
 
+		private protected virtual void MeasureSupplementaryViews()
+		{
+			RemeasureLayout(_emptyViewFormsElement, _emptyUIView);
+		}
+
+		private protected virtual void LayoutSupplementaryViews()
+		{
+			LayoutEmptyView();
+		}
+
 		void InvalidateLayoutIfItemsMeasureChanged()
 		{
 			var visibleCells = CollectionView.VisibleCells;
@@ -237,6 +260,21 @@ void InvalidateLayoutIfItemsMeasureChanged()
 			}
 		}
 
+		bool IsRefreshing()
+		{
+			var subviews = CollectionView.Subviews;
+			var subviewsLength = subviews.Length;
+			for (int i = 0; i < subviewsLength; i++)
+			{
+				if (subviews[i] is UIRefreshControl { Refreshing: true })
+				{
+					return true;
+				}
+			}
+
+			return false;
+		}
+
 		void MauiCollectionView.ICustomMauiCollectionViewDelegate.MovedToWindow(UIView view)
 		{
 			if (CollectionView?.Window != null)
@@ -549,15 +587,58 @@ protected virtual CGRect DetermineEmptyViewFrame()
 
 		protected void RemeasureLayout(VisualElement formsElement)
 		{
+			Size size;
 			if (IsHorizontal)
 			{
 				var request = formsElement.Measure(double.PositiveInfinity, CollectionView.Frame.Height);
-				formsElement.Arrange(new Rect(0, 0, request.Width, CollectionView.Frame.Height));
+				size = new Size(request.Width, CollectionView.Frame.Height);
 			}
 			else
 			{
 				var request = formsElement.Measure(CollectionView.Frame.Width, double.PositiveInfinity);
-				formsElement.Arrange(new Rect(0, 0, CollectionView.Frame.Width, request.Height));
+				size = new Size(CollectionView.Frame.Width, request.Height);
+			}
+
+			var platformView = formsElement.ToPlatform();
+			if (platformView.Superview is GeneralWrapperView generalWrapperView)
+			{
+				var originalFrame = generalWrapperView.Frame;
+				generalWrapperView.Frame = new CGRect(originalFrame.X, originalFrame.Y, (nfloat)size.Width, (nfloat)size.Height);
+			}
+			else
+			{
+				var frame = new Rect(platformView.Frame.X, platformView.Frame.Y, size.Width, size.Height);
+				formsElement.Arrange(frame);
+			}
+		}
+
+		void RemeasureLayout(UIView nativeView)
+		{
+			var originalFrame = nativeView.Frame;
+
+			if (IsHorizontal)
+			{
+				var constraints = new CGSize(double.PositiveInfinity, CollectionView.Frame.Height);
+				var size = nativeView.SizeThatFits(constraints);
+				nativeView.Frame = new CGRect(originalFrame.X, originalFrame.Y, size.Width, CollectionView.Frame.Height);
+			}
+			else
+			{
+				var constraints = new CGSize(CollectionView.Frame.Width, double.PositiveInfinity);
+				var size = nativeView.SizeThatFits(constraints);
+				nativeView.Frame = new CGRect(originalFrame.X, originalFrame.Y, CollectionView.Frame.Width, size.Height);
+			}
+		}
+
+		private protected void RemeasureLayout(VisualElement formsElement, UIView nativeElement)
+		{
+			if (formsElement is not null)
+			{
+				RemeasureLayout(formsElement);
+			}
+			else if (nativeElement is not null)
+			{
+				RemeasureLayout(nativeElement);
 			}
 		}
 
@@ -684,7 +765,7 @@ void ShowEmptyView()
 				ItemsView.AddLogicalChild(_emptyViewFormsElement);
 			}
 
-			LayoutEmptyView();
+			_emptyUIView.InvalidateMeasure();
 
 			AlignEmptyView();
 			_emptyViewDisplayed = true;
@@ -723,9 +804,7 @@ void LayoutEmptyView()
 			var frame = DetermineEmptyViewFrame();
 
 			_emptyUIView.Frame = frame;
-
-			if (_emptyViewFormsElement != null && ((IElementController)ItemsView).LogicalChildren.IndexOf(_emptyViewFormsElement) != -1)
-				_emptyViewFormsElement.Layout(frame.ToRectangle());
+			_emptyViewFormsElement?.Arrange(frame.ToRectangle());
 		}
 
 		TemplatedCell CreateAppropriateCellForLayout()

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

@@ -74,25 +74,18 @@ protected override CGRect DetermineEmptyViewFrame()
 				Math.Abs(CollectionView.Frame.Height - (headerHeight + footerHeight)));
 		}
 
-		public override void ViewWillLayoutSubviews()
+		private protected override void MeasureSupplementaryViews()
 		{
-			var hasHeaderOrFooter = _footerViewFormsElement is not null || _headerViewFormsElement is not null;
-			if (hasHeaderOrFooter && CollectionView is MauiCollectionView { NeedsCellLayout: true } collectionView)
-			{
-				if (_headerViewFormsElement is not null)
-				{
-					RemeasureLayout(_headerViewFormsElement);
-				}
+			base.MeasureSupplementaryViews();
 
-				if (_footerViewFormsElement is not null)
-				{
-					RemeasureLayout(_footerViewFormsElement);
-				}
-
-				UpdateHeaderFooterPosition();
-			}
+			RemeasureLayout(_headerViewFormsElement, _headerUIView);
+			RemeasureLayout(_footerViewFormsElement, _footerUIView);
+		}
 
-			base.ViewWillLayoutSubviews();
+		private protected override void LayoutSupplementaryViews()
+		{
+			base.LayoutSupplementaryViews();
+			UpdateHeaderFooterPosition();
 		}
 
 		internal void UpdateFooterView()
@@ -131,14 +124,7 @@ internal void UpdateSubview(object view, DataTemplate viewTemplate, nint viewTag
 				ItemsView.AddLogicalChild(formsElement);
 			}
 
-			if (formsElement != null)
-			{
-				RemeasureLayout(formsElement);
-			}
-			else
-			{
-				uiView?.SizeToFit();
-			}
+			RemeasureLayout(formsElement, uiView);
 		}
 
 		void UpdateHeaderFooterPosition()
@@ -149,22 +135,10 @@ void UpdateHeaderFooterPosition()
 			{
 				var currentInset = CollectionView.ContentInset;
 
-				nfloat headerWidth = ((ItemsView?.Header is View) ? _headerViewFormsElement?.ToPlatform() : _headerUIView)?.Frame.Width ?? 0f;
-				nfloat footerWidth = ((ItemsView?.Footer is View) ? _footerViewFormsElement?.ToPlatform() : _footerUIView)?.Frame.Width ?? 0f;
+				nfloat headerWidth = _headerUIView?.Frame.Width ?? 0f;
+				nfloat footerWidth = _footerUIView?.Frame.Width ?? 0f;
 				nfloat emptyWidth = emptyView?.Frame.Width ?? 0f;
 
-				if (_headerUIView != null && _headerUIView.Frame.X != headerWidth)
-				{
-					_headerUIView.Frame = new CoreGraphics.CGRect(-headerWidth, 0, headerWidth, CollectionView.Frame.Height);
-				}
-
-				if (_footerUIView != null && (_footerUIView.Frame.X != ItemsViewLayout.CollectionViewContentSize.Width || emptyWidth > 0))
-				{
-					_footerUIView.Frame = new CoreGraphics.CGRect(
-						ItemsViewLayout.CollectionViewContentSize.Width + emptyWidth, 0, footerWidth,
-						CollectionView.Frame.Height);
-				}
-
 				if (CollectionView.ContentInset.Left != headerWidth || CollectionView.ContentInset.Right != footerWidth)
 				{
 					var currentOffset = CollectionView.ContentOffset;
@@ -177,14 +151,31 @@ void UpdateHeaderFooterPosition()
 
 					// if the header grows it will scroll off the screen because if you change the content inset iOS adjusts the content offset so the list doesn't move
 					// this changes the offset of the list by however much the header size has changed
-					CollectionView.ContentOffset = new CoreGraphics.CGPoint(xOffset, CollectionView.ContentOffset.Y);
+					CollectionView.ContentOffset = new CGPoint(xOffset, CollectionView.ContentOffset.Y);
+				}
+
+				if (_headerUIView != null && _headerUIView.Frame.X != -headerWidth)
+				{
+					_headerUIView.Frame = new CGRect(-headerWidth, 0, headerWidth, CollectionView.Frame.Height);
+				}
+
+				if (_footerUIView != null && IsViewLoaded && View.Window != null)
+				{
+					var width = ItemsViewLayout.CollectionViewContentSize.Height;
+					var footerX = width + emptyWidth;
+					var currentFrame = _footerUIView.Frame;
+
+					if (currentFrame.X != footerX)
+					{
+						_footerUIView.Frame = new CGRect(footerX, 0, footerWidth, CollectionView.Frame.Height);
+					}
 				}
 			}
 			else
 			{
 				var currentInset = CollectionView.ContentInset;
-				nfloat headerHeight = ((ItemsView?.Header is View) ? _headerViewFormsElement?.ToPlatform() : _headerUIView)?.Frame.Height ?? 0f;
-				nfloat footerHeight = ((ItemsView?.Footer is View) ? _footerViewFormsElement?.ToPlatform() : _footerUIView)?.Frame.Height ?? 0f;
+				nfloat headerHeight = _headerUIView?.Frame.Height ?? 0f;
+				nfloat footerHeight = _footerUIView?.Frame.Height ?? 0f;
 				nfloat emptyHeight = emptyView?.Frame.Height ?? 0f;
 
 				if (CollectionView.ContentInset.Top != headerHeight || CollectionView.ContentInset.Bottom != footerHeight)
@@ -202,25 +193,25 @@ void UpdateHeaderFooterPosition()
 
 					if (currentOffset.Y.Value < headerHeight)
 					{
-						CollectionView.ContentOffset = new CoreGraphics.CGPoint(CollectionView.ContentOffset.X, yOffset);
+						CollectionView.ContentOffset = new CGPoint(CollectionView.ContentOffset.X, yOffset);
 					}
 				}
 
-				if (_headerUIView != null && (_headerUIView.Frame.Y != -headerHeight || _headerUIView.Frame.Width != CollectionView.Frame.Width))
+				if (_headerUIView != null && _headerUIView.Frame.Y != -headerHeight)
 				{
-					_headerUIView.Frame = new CoreGraphics.CGRect(0, -headerHeight, CollectionView.Frame.Width, headerHeight);
+					_headerUIView.Frame = new CGRect(0, -headerHeight, CollectionView.Frame.Width, headerHeight);
 				}
 
-				nfloat height = 0;
-
-				if (IsViewLoaded && View.Window != null)
+				if (_footerUIView != null && IsViewLoaded && View.Window != null)
 				{
-					height = ItemsViewLayout.CollectionViewContentSize.Height;
-				}
+					var height = ItemsViewLayout.CollectionViewContentSize.Height;
+					var footerY = height + emptyHeight;
+					var currentFrame = _footerUIView.Frame;
 
-				if (_footerUIView != null && (_footerUIView.Frame.Y != height || emptyHeight > 0 || _footerUIView.Frame.Height != footerHeight || _footerUIView.Frame.Width != CollectionView.Frame.Width))
-				{
-					_footerUIView.Frame = new CoreGraphics.CGRect(0, height + emptyHeight, CollectionView.Frame.Width, footerHeight);
+					if (currentFrame.Y != footerY)
+					{
+						_footerUIView.Frame = new CGRect(0, footerY, CollectionView.Frame.Width, footerHeight);
+					}
 				}
 			}
 		}