[Android] CollectionView: Fix item spacing applied on outer edges causing scroll/rendering issues

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

@@ -15,7 +15,7 @@
 namespace Microsoft.Maui.Controls.Handlers.Items
 {
 
-	public class MauiRecyclerView<TItemsView, TAdapter, TItemsViewSource> : RecyclerView, IMauiRecyclerView<TItemsView>
+	public class MauiRecyclerView<TItemsView, TAdapter, TItemsViewSource> : RecyclerView, IMauiRecyclerView<TItemsView>, IMauiRecyclerView
 		where TItemsView : ItemsView
 		where TAdapter : ItemsViewAdapter<TItemsView, TItemsViewSource>
 		where TItemsViewSource : IItemsViewSource
@@ -84,11 +84,8 @@ public virtual void TearDownOldElement(TItemsView oldElement)
 				ItemsViewAdapter?.Dispose();
 			}
 
-			if (_snapManager != null)
-			{
-				_snapManager.Dispose();
-				_snapManager = null;
-			}
+			_snapManager?.Dispose();
+			_snapManager = null;
 
 			if (_itemDecoration != null)
 			{
@@ -102,11 +99,8 @@ public virtual void TearDownOldElement(TItemsView oldElement)
 				_itemTouchHelper = null;
 			}
 
-			if (_itemTouchHelperCallback != null)
-			{
-				_itemTouchHelperCallback.Dispose();
-				_itemTouchHelperCallback = null;
-			}
+			_itemTouchHelperCallback?.Dispose();
+			_itemTouchHelperCallback = null;
 		}
 
 		public virtual void SetUpNewElement(TItemsView newElement)
@@ -276,22 +270,26 @@ public virtual void UpdateCanReorderItems()
 					_itemTouchHelper.Dispose();
 					_itemTouchHelper = null;
 				}
-				if (_itemTouchHelperCallback != null)
-				{
-					_itemTouchHelperCallback.Dispose();
-					_itemTouchHelperCallback = null;
-				}
+
+				_itemTouchHelperCallback?.Dispose();
+				_itemTouchHelperCallback = null;
 			}
 		}
 
 		public virtual void UpdateLayoutManager()
 		{
-			_layoutPropertyChangedProxy?.Unsubscribe();
+			var itemsLayout = _getItemsLayout();
+
+			if (itemsLayout == ItemsLayout)
+			{
+				return;
+			}
 
-			ItemsLayout = _getItemsLayout();
+			_layoutPropertyChangedProxy?.Unsubscribe();
+			ItemsLayout = itemsLayout;
 
 			// Keep track of the ItemsLayout's property changes
-			if (ItemsLayout != null)
+			if (ItemsLayout is not null)
 			{
 				_layoutPropertyChanged ??= LayoutPropertyChanged;
 				_layoutPropertyChangedProxy = new WeakNotifyPropertyChangedProxy(ItemsLayout, _layoutPropertyChanged);
@@ -427,9 +425,9 @@ protected virtual int DetermineTargetPosition(ScrollToRequestEventArgs args)
 			if (args.Mode == ScrollToMode.Position)
 			{
 				// Do not use `IGroupableItemsViewSource` since `UngroupedItemsSource` also implements that interface
-				if (ItemsViewAdapter.ItemsSource is UngroupedItemsSource)
+				if (ItemsViewAdapter.ItemsSource is UngroupedItemsSource ungroupedSource)
 				{
-					return args.Index;
+					return ungroupedSource.HasHeader ? args.Index + 1 : args.Index;
 				}
 				else if (ItemsViewAdapter.ItemsSource is IGroupableItemsViewSource groupItemSource)
 				{
@@ -473,12 +471,26 @@ protected virtual void UpdateItemSpacing()
 
 			if (_itemDecoration is SpacingItemDecoration spacingDecoration)
 			{
-				// SpacingItemDecoration applies spacing to all items & all 4 sides of the items.
-				// We need to adjust the padding on the RecyclerView so this spacing isn't visible around the outer edge of our control.
-				// Horizontal & vertical spacing should only exist between items. 
-				var horizontalPadding = -spacingDecoration.HorizontalOffset;
-				var verticalPadding = -spacingDecoration.VerticalOffset;
-				SetPadding(horizontalPadding, verticalPadding, horizontalPadding, verticalPadding);
+				// SpacingItemDecoration now removes spacing on outer edges (first/last row or column),
+				// so we only need negative padding on the cross-axis for grid layouts to compensate
+				// for the spacing between columns (vertical grid) or rows (horizontal grid).
+				if (ItemsLayout is GridItemsLayout gridItemsLayout)
+				{
+					if (gridItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal)
+					{
+						var verticalPadding = -spacingDecoration.VerticalOffset;
+						SetPadding(0, verticalPadding, 0, verticalPadding);
+					}
+					else
+					{
+						var horizontalPadding = -spacingDecoration.HorizontalOffset;
+						SetPadding(horizontalPadding, 0, horizontalPadding, 0);
+					}
+				}
+				else
+				{
+					SetPadding(0, 0, 0, 0);
+				}
 			}
 		}
 
@@ -513,6 +525,7 @@ protected virtual void LayoutPropertyChanged(object sender, PropertyChangedEvent
 				if (GetLayoutManager() is GridLayoutManager gridLayoutManager)
 				{
 					gridLayoutManager.SpanCount = ((GridItemsLayout)ItemsLayout).Span;
+					UpdateItemSpacing();
 				}
 			}
 			else if (propertyChanged.IsOneOf(Microsoft.Maui.Controls.ItemsLayout.SnapPointsTypeProperty, Microsoft.Maui.Controls.ItemsLayout.SnapPointsAlignmentProperty))
@@ -585,6 +598,34 @@ internal void UpdateEmptyViewVisibility()
 				SwapAdapter(ItemsViewAdapter, true);
 				UpdateLayoutManager();
 			}
+			else if (showEmptyView && currentAdapter == _emptyViewAdapter)
+			{
+				if (ShouldUpdateEmptyView())
+				{
+					// Header/footer properties changed - detach and reattach adapter to force RecyclerView to recalculate the positions.
+					SetAdapter(null);
+					SwapAdapter(_emptyViewAdapter, true);
+					UpdateEmptyView();
+				}
+			}
+		}
+
+		bool ShouldUpdateEmptyView()
+		{
+			if (ItemsView is StructuredItemsView structuredItemsView)
+			{
+				if (_emptyViewAdapter.Header != structuredItemsView.Header ||
+					_emptyViewAdapter.HeaderTemplate != structuredItemsView.HeaderTemplate ||
+					_emptyViewAdapter.Footer != structuredItemsView.Footer ||
+					_emptyViewAdapter.FooterTemplate != structuredItemsView.FooterTemplate ||
+					_emptyViewAdapter.EmptyView != ItemsView.EmptyView ||
+					_emptyViewAdapter.EmptyViewTemplate != ItemsView.EmptyViewTemplate)
+				{
+					return true;
+				}
+			}
+
+			return false;
 		}
 
 		internal void AdjustScrollForItemUpdate()

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

@@ -13,6 +13,10 @@ public class SpacingItemDecoration : RecyclerView.ItemDecoration
 
 		public int VerticalOffset { get; }
 
+		int _span = 1;
+
+		ItemsLayoutOrientation _orientation;
+
 		public SpacingItemDecoration(Context context, IItemsLayout itemsLayout)
 		{
 			// The original "SpacingItemDecoration" applied spacing based on an item's current span index.
@@ -35,6 +39,8 @@ public SpacingItemDecoration(Context context, IItemsLayout itemsLayout)
 				case GridItemsLayout gridItemsLayout:
 					horizontalOffset = gridItemsLayout.HorizontalItemSpacing / 2.0;
 					verticalOffset = gridItemsLayout.VerticalItemSpacing / 2.0;
+					_span = gridItemsLayout.Span;
+					_orientation = gridItemsLayout.Orientation;
 					break;
 				case LinearItemsLayout listItemsLayout:
 					if (listItemsLayout.Orientation == ItemsLayoutOrientation.Horizontal)
@@ -47,10 +53,12 @@ public SpacingItemDecoration(Context context, IItemsLayout itemsLayout)
 						horizontalOffset = 0;
 						verticalOffset = listItemsLayout.ItemSpacing / 2.0;
 					}
+					_orientation = listItemsLayout.Orientation;
 					break;
 				default:
 					horizontalOffset = 0;
 					verticalOffset = 0;
+					_orientation = ItemsLayoutOrientation.Vertical;
 					break;
 			}
 
@@ -62,10 +70,39 @@ public override void GetItemOffsets(ARect outRect, AView view, RecyclerView pare
 		{
 			base.GetItemOffsets(outRect, view, parent, state);
 
+			int position = parent.GetChildAdapterPosition(view);
+			if (position == RecyclerView.NoPosition)
+				return;
+
+			int itemCount = state.ItemCount;
+			if (itemCount <= 0)
+				return;
+
 			outRect.Left = HorizontalOffset;
 			outRect.Right = HorizontalOffset;
 			outRect.Bottom = VerticalOffset;
 			outRect.Top = VerticalOffset;
+
+			// Remove spacing on the outer edges so spacing only appears between items.
+			// A linear layout is effectively span=1, so the same math works for both.
+			int rowCol = _span <= 1 ? position : position / _span;
+			int totalRowsCols = _span <= 1 ? itemCount : (itemCount + _span - 1) / _span;
+			int lastRowCol = totalRowsCols - 1;
+
+			if (_orientation == ItemsLayoutOrientation.Vertical)
+			{
+				if (rowCol == 0)
+					outRect.Top = 0;
+				if (rowCol == lastRowCol)
+					outRect.Bottom = 0;
+			}
+			else
+			{
+				if (rowCol == 0)
+					outRect.Left = 0;
+				if (rowCol == lastRowCol)
+					outRect.Right = 0;
+			}
 		}
 	}
 }