Refactor ItemsLayout handling: dynamic default + virtual view-managed subscriptions

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

@@ -43,10 +43,9 @@ public class MauiRecyclerView<TItemsView, TAdapter, TItemsViewSource> : Recycler
 
 		ItemTouchHelper _itemTouchHelper;
 		SimpleItemTouchHelperCallback _itemTouchHelperCallback;
-		WeakNotifyPropertyChangedProxy _layoutPropertyChangedProxy;
-		PropertyChangedEventHandler _layoutPropertyChanged;
 
-		~MauiRecyclerView() => _layoutPropertyChangedProxy?.Unsubscribe();
+		//TODO: Remove this in .NET 10
+		~MauiRecyclerView() {}
 
 		public MauiRecyclerView(Context context, Func<IItemsLayout> getItemsLayout, Func<TAdapter> getAdapter) : base(new ContextThemeWrapper(context, Resource.Style.collectionViewTheme))
 		{
@@ -59,13 +58,6 @@ public MauiRecyclerView(Context context, Func<IItemsLayout> getItemsLayout, Func
 
 		public virtual void TearDownOldElement(TItemsView oldElement)
 		{
-			// Stop listening for layout property changes
-			if (_layoutPropertyChangedProxy is not null)
-			{
-				_layoutPropertyChangedProxy.Unsubscribe();
-				_layoutPropertyChanged = null;
-			}
-
 			// Stop listening for ScrollTo requests
 			oldElement.ScrollToRequested -= ScrollToRequested;
 
@@ -286,21 +278,12 @@ public virtual void UpdateCanReorderItems()
 
 		public virtual void UpdateLayoutManager()
 		{
-			_layoutPropertyChangedProxy?.Unsubscribe();
-
 			ItemsLayout = _getItemsLayout();
 
-			// Keep track of the ItemsLayout's property changes
-			if (ItemsLayout != null)
-			{
-				_layoutPropertyChanged ??= LayoutPropertyChanged;
-				_layoutPropertyChangedProxy = new WeakNotifyPropertyChangedProxy(ItemsLayout, _layoutPropertyChanged);
-			}
-
 			SetLayoutManager(SelectLayoutManager(ItemsLayout));
 
 			UpdateFlowDirection();
-			UpdateItemSpacing();
+			UpdateItemsLayoutProperties();
 		}
 
 		protected virtual RecyclerViewScrollListener<TItemsView, TItemsViewSource> CreateScrollListener() => new(ItemsView, ItemsViewAdapter);
@@ -506,24 +489,22 @@ protected virtual void ScrollToRequested(object sender, ScrollToRequestEventArgs
 			ScrollTo(args);
 		}
 
+		//TODO: Remove this in .NET 10
 		protected virtual void LayoutPropertyChanged(object sender, PropertyChangedEventArgs propertyChanged)
 		{
-			if (propertyChanged.Is(GridItemsLayout.SpanProperty))
-			{
-				if (GetLayoutManager() is GridLayoutManager gridLayoutManager)
-				{
-					gridLayoutManager.SpanCount = ((GridItemsLayout)ItemsLayout).Span;
-				}
-			}
-			else if (propertyChanged.IsOneOf(Microsoft.Maui.Controls.ItemsLayout.SnapPointsTypeProperty, Microsoft.Maui.Controls.ItemsLayout.SnapPointsAlignmentProperty))
-			{
-				UpdateSnapBehavior();
-			}
-			else if (propertyChanged.IsOneOf(LinearItemsLayout.ItemSpacingProperty,
-				GridItemsLayout.HorizontalItemSpacingProperty, GridItemsLayout.VerticalItemSpacingProperty))
+
+		}
+
+		void UpdateItemsLayoutProperties()
+		{
+			if (ItemsLayout is GridItemsLayout gridItemsLayout && GetLayoutManager() is GridLayoutManager gridLayoutManager)
 			{
-				UpdateItemSpacing();
+				gridLayoutManager.SpanCount = gridItemsLayout.Span;
 			}
+
+			UpdateSnapBehavior();
+
+			UpdateItemSpacing();
 		}
 
 		protected override void OnLayout(bool changed, int l, int t, int r, int b)

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

@@ -350,7 +350,6 @@ protected virtual void UpdateItemsLayout()
 			_defaultVerticalScrollVisibility = null;
 
 			UpdateItemTemplate();
-			UpdateItemsSource();
 			UpdateScrollBarVisibility();
 			UpdateEmptyView();
 		}

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

@@ -16,47 +16,27 @@ public partial class StructuredItemsViewHandler<TItemsView> : ItemsViewHandler<T
 	{
 		View _currentHeader;
 		View _currentFooter;
-		WeakNotifyPropertyChangedProxy _layoutPropertyChangedProxy;
-		PropertyChangedEventHandler _layoutPropertyChanged;
 
-		~StructuredItemsViewHandler() => _layoutPropertyChangedProxy?.Unsubscribe();
+		//TODO: Remove this in .NET 10
+		~StructuredItemsViewHandler() { }
 
 		protected override IItemsLayout Layout { get => ItemsView?.ItemsLayout; }
 
+		//TODO: Remove this in .NET 10
 		protected override void ConnectHandler(ListViewBase platformView)
 		{
 			base.ConnectHandler(platformView);
-
-			if (Layout is not null)
-			{
-				_layoutPropertyChanged ??= LayoutPropertyChanged;
-				_layoutPropertyChangedProxy = new WeakNotifyPropertyChangedProxy(Layout, _layoutPropertyChanged);
-			}
-			else if (_layoutPropertyChangedProxy is not null)
-			{
-				_layoutPropertyChangedProxy.Unsubscribe();
-				_layoutPropertyChangedProxy = null;
-			}
 		}
 
+		//TODO: Remove this in .NET 10
 		protected override void DisconnectHandler(ListViewBase platformView)
 		{
 			base.DisconnectHandler(platformView);
-
-			if (_layoutPropertyChangedProxy is not null)
-			{
-				_layoutPropertyChangedProxy.Unsubscribe();
-				_layoutPropertyChangedProxy = null;
-			}
 		}
 
-		void LayoutPropertyChanged(object sender, PropertyChangedEventArgs e)
+		void UpdateItemsLayoutProperties()
 		{
-			if (e.PropertyName == GridItemsLayout.SpanProperty.PropertyName)
-				UpdateItemsLayoutSpan();
-			else if (e.PropertyName == GridItemsLayout.HorizontalItemSpacingProperty.PropertyName || e.PropertyName == GridItemsLayout.VerticalItemSpacingProperty.PropertyName)
-				UpdateItemsLayoutItemSpacing();
-			else if (e.PropertyName == LinearItemsLayout.ItemSpacingProperty.PropertyName)
+				UpdateItemsLayoutSpan();		
 				UpdateItemsLayoutItemSpacing();
 		}
 
@@ -73,6 +53,7 @@ public static void MapFooterTemplate(StructuredItemsViewHandler<TItemsView> hand
 		public static void MapItemsLayout(StructuredItemsViewHandler<TItemsView> handler, StructuredItemsView itemsView)
 		{
 			handler.UpdateItemsLayout();
+			handler.UpdateItemsLayoutProperties();
 		}
 
 		public static void MapItemSizingStrategy(StructuredItemsViewHandler<TItemsView> handler, StructuredItemsView itemsView)
@@ -298,13 +279,13 @@ void UpdateItemsLayoutItemSpacing()
 
 			if (Layout is LinearItemsLayout linearItemsLayout)
 			{
-				switch (ListViewBase)
+				switch (linearItemsLayout.Orientation)
 				{
-					case FormsListView formsListView:
-						formsListView.ItemContainerStyle = GetVerticalItemContainerStyle(linearItemsLayout);
+					case ItemsLayoutOrientation.Vertical:
+						ListViewBase.ItemContainerStyle = GetVerticalItemContainerStyle(linearItemsLayout);
 						break;
-					case WListView listView:
-						listView.ItemContainerStyle = GetHorizontalItemContainerStyle(linearItemsLayout);
+					case ItemsLayoutOrientation.Horizontal:
+						ListViewBase.ItemContainerStyle = GetHorizontalItemContainerStyle(linearItemsLayout);
 						break;
 				}
 			}

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

@@ -8,13 +8,25 @@ namespace Microsoft.Maui.Controls.Handlers.Items
 	public class CarouselViewLayout : ItemsViewLayout
 	{
 		readonly WeakReference<CarouselView> _carouselView;
-		readonly ItemsLayout _itemsLayout;
+		readonly WeakReference<ItemsLayout> _itemsLayout;
+		ItemsLayout ItemsLayout
+		{
+			get
+			{
+				_itemsLayout.TryGetTarget(out var itemsLayout);
+				return itemsLayout;
+			}
+			set
+			{
+				_itemsLayout.SetTarget(value);
+			}
+		}
 		CGPoint? _pendingOffset;
 
 		public CarouselViewLayout(ItemsLayout itemsLayout, CarouselView carouselView) : base(itemsLayout)
 		{
 			_carouselView = new(carouselView);
-			_itemsLayout = itemsLayout;
+			_itemsLayout = new(itemsLayout);
 		}
 
 		public override void ConstrainTo(CGSize size)
@@ -38,7 +50,7 @@ public override void ConstrainTo(CGSize size)
 
 		public override nfloat GetMinimumInteritemSpacingForSection(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
 		{
-			if (_itemsLayout is LinearItemsLayout linearItemsLayout)
+			if (ItemsLayout is LinearItemsLayout linearItemsLayout)
 				return (nfloat)linearItemsLayout.ItemSpacing;
 
 			return base.GetMinimumInteritemSpacingForSection(collectionView, layout, section);

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

@@ -10,11 +10,24 @@ namespace Microsoft.Maui.Controls.Handlers.Items
 {
 	public class GridViewLayout : ItemsViewLayout
 	{
-		readonly GridItemsLayout _itemsLayout;
+		readonly  WeakReference<GridItemsLayout> _itemsLayout  = new WeakReference<GridItemsLayout>(null);
+
+		GridItemsLayout ItemsLayout
+		{
+			get
+			{
+				_itemsLayout.TryGetTarget(out var itemsLayout);
+				return itemsLayout;
+			}
+			set
+			{
+				_itemsLayout.SetTarget(value);
+			}
+		}
 
 		public GridViewLayout(GridItemsLayout itemsLayout, ItemSizingStrategy itemSizingStrategy) : base(itemsLayout, itemSizingStrategy)
 		{
-			_itemsLayout = itemsLayout;
+			ItemsLayout = itemsLayout;
 		}
 
 		protected override void HandlePropertyChanged(PropertyChangedEventArgs propertyChanged)
@@ -34,18 +47,19 @@ protected override void HandlePropertyChanged(PropertyChangedEventArgs propertyC
 
 		public override void ConstrainTo(CGSize size)
 		{
+			var itemsLayout = ItemsLayout;
 			var availableSpace = ScrollDirection == UICollectionViewScrollDirection.Vertical
 					? size.Width : size.Height;
 
 			var spacing = (nfloat)(ScrollDirection == UICollectionViewScrollDirection.Vertical
-					? _itemsLayout.HorizontalItemSpacing
-					: _itemsLayout.VerticalItemSpacing);
+					? itemsLayout.HorizontalItemSpacing
+					: itemsLayout.VerticalItemSpacing);
 
-			spacing = ReduceSpacingToFitIfNeeded(availableSpace, spacing, _itemsLayout.Span);
+			spacing = ReduceSpacingToFitIfNeeded(availableSpace, spacing, itemsLayout.Span);
 
-			spacing *= (_itemsLayout.Span - 1);
+			spacing *= (itemsLayout.Span - 1);
 
-			ConstrainedDimension = (availableSpace - spacing) / _itemsLayout.Span;
+			ConstrainedDimension = (availableSpace - spacing) / itemsLayout.Span;
 
 			// We need to truncate the decimal part of ConstrainedDimension
 			// or we occasionally run into situations where the rows/columns don't fit	
@@ -194,22 +208,23 @@ public override UICollectionViewLayoutInvalidationContext GetInvalidationContext
 
 		public override nfloat GetMinimumInteritemSpacingForSection(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
 		{
+			var itemsLayout = ItemsLayout;
 			var requestedSpacing = ScrollDirection == UICollectionViewScrollDirection.Horizontal
-				? (nfloat)_itemsLayout.VerticalItemSpacing
-				: (nfloat)_itemsLayout.HorizontalItemSpacing;
+				? (nfloat)itemsLayout.VerticalItemSpacing
+				: (nfloat)itemsLayout.HorizontalItemSpacing;
 
 			var availableSpace = ScrollDirection == UICollectionViewScrollDirection.Horizontal
 				? collectionView.Frame.Height
 				: collectionView.Frame.Width;
 
-			return ReduceSpacingToFitIfNeeded(availableSpace, requestedSpacing, _itemsLayout.Span);
+			return ReduceSpacingToFitIfNeeded(availableSpace, requestedSpacing, itemsLayout.Span);
 		}
 
 		void CenterAlignCellsInColumn(UICollectionViewLayoutAttributes preferredAttributes)
 		{
 			// Determine the set of cells above this one
 			var index = preferredAttributes.IndexPath;
-			var span = _itemsLayout.Span;
+			var span = ItemsLayout.Span;
 
 			var column = index.Item / span;
 			var start = (int)column * span;
@@ -257,6 +272,7 @@ bool NeedsSingleItemHorizontalAlignmentAdjustment(UICollectionViewLayoutAttribut
 
 		bool NeedsPartialColumnAdjustment(int section = 0)
 		{
+			var itemsLayout = ItemsLayout;
 			if (ScrollDirection == UICollectionViewScrollDirection.Vertical)
 			{
 				// The bug only occurs with Horizontal scrolling
@@ -280,13 +296,13 @@ bool NeedsPartialColumnAdjustment(int section = 0)
 
 			var itemCount = CollectionView.NumberOfItemsInSection(section);
 
-			if (itemCount < _itemsLayout.Span)
+			if (itemCount < itemsLayout.Span)
 			{
 				// If there is just one partial column, no problem; UICollectionViewFlowLayout gets it right
 				return false;
 			}
 
-			if (itemCount % _itemsLayout.Span == 0)
+			if (itemCount % itemsLayout.Span == 0)
 			{
 				// All of the columns are full; the bug only occurs when we have a partial column
 				return false;