fix(combobox)!: Make ComboBox inherit from Selector

BREAKING CHANGE: ComboBox now inherits from Selector rather than ListViewBase, to match the UWP/WinUI inheritance hierarchy.

src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBox.cs

@@ -39,8 +39,7 @@
 
 namespace Windows.UI.Xaml.Controls
 {
-	// Temporarily inheriting from ListViewBase instead of Selector to leverage existing selection and virtualization code
-	public partial class ComboBox : ListViewBase // TODO: Selector
+	public partial class ComboBox : Selector
 	{
 		public event EventHandler<object>? DropDownClosed;
 		public event EventHandler<object>? DropDownOpened;
@@ -62,7 +61,6 @@ public ComboBox()
 		{
 			ResourceResolver.ApplyResource(this, LightDismissOverlayBackgroundProperty, "ComboBoxLightDismissOverlayBackground", isThemeResourceExtension: true);
 
-			IsItemClickEnabled = true;
 			DefaultStyleKey = typeof(ComboBox);
 		}
 
@@ -188,15 +186,51 @@ private void OnPopupClosed(object? sender, object e)
 			IsDropDownOpen = false;
 		}
 
-		protected override void OnHeaderChanged(object oldHeader, object newHeader)
+
+		public object Header
+		{
+			get { return (object)this.GetValue(HeaderProperty); }
+			set { this.SetValue(HeaderProperty, value); }
+		}
+
+		public static DependencyProperty HeaderProperty { get; } =
+			DependencyProperty.Register(
+				"Header",
+				typeof(object),
+				typeof(ComboBox),
+				new FrameworkPropertyMetadata(
+					defaultValue: null,
+					options: FrameworkPropertyMetadataOptions.None,
+					propertyChangedCallback: (s, e) => ((ComboBox)s)?.OnHeaderChanged((object)e.OldValue, (object)e.NewValue)
+				)
+			);
+
+		private void OnHeaderChanged(object oldHeader, object newHeader)
 		{
-			base.OnHeaderChanged(oldHeader, newHeader);
 			UpdateHeaderVisibility();
 		}
 
-		protected override void OnHeaderTemplateChanged(DataTemplate oldHeaderTemplate, DataTemplate newHeaderTemplate)
+
+		public DataTemplate HeaderTemplate
+		{
+			get { return (DataTemplate)this.GetValue(HeaderTemplateProperty); }
+			set { this.SetValue(HeaderTemplateProperty, value); }
+		}
+
+		public static DependencyProperty HeaderTemplateProperty { get; } =
+			DependencyProperty.Register(
+				"HeaderTemplate",
+				typeof(DataTemplate),
+				typeof(ComboBox),
+				new FrameworkPropertyMetadata(
+					defaultValue: (DataTemplate?)null,
+					options: FrameworkPropertyMetadataOptions.ValueDoesNotInheritDataContext,
+					propertyChangedCallback: (s, e) => ((ComboBox)s)?.OnHeaderTemplateChanged((DataTemplate)e.OldValue, (DataTemplate)e.NewValue)
+				)
+			);
+
+		private void OnHeaderTemplateChanged(DataTemplate oldHeaderTemplate, DataTemplate newHeaderTemplate)
 		{
-			base.OnHeaderTemplateChanged(oldHeaderTemplate, newHeaderTemplate);
 			UpdateHeaderVisibility();
 		}
 
@@ -384,11 +418,6 @@ partial void OnIsDropDownOpenChangedPartial(bool oldIsDropDownOpen, bool newIsDr
 				OnDropDownOpened(args);
 
 				RestoreSelectedItem();
-
-				if (SelectedItem != null)
-				{
-					ScrollIntoView(SelectedItem);
-				}
 			}
 			else
 			{
@@ -560,8 +589,10 @@ public Size Measure(Size available, Size visibleSize)
 					// since the layouting on those platforms is not yet as aligned with UWP as on WASM/Skia, and in particular
 					// virtualizing panels aren't used in the ComboBox yet (#556 and #1133), we skip it for now
 					{
+#pragma warning disable CS0162 // Unreachable code detected
 						child.HorizontalAlignment = HorizontalAlignment.Left;
 						child.VerticalAlignment = VerticalAlignment.Top;
+#pragma warning restore CS0162 // Unreachable code detected
 					}
 				}
 

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.cs

@@ -369,6 +369,8 @@ partial void OnSelectionModeChangedPartial(ListViewSelectionMode oldSelectionMod
 
 		internal override void OnItemClicked(int clickedIndex)
 		{
+			// Note: don't call base.OnItemClicked(), because we override the default single-selection-only handling
+
 			var item = ItemFromIndex(clickedIndex);
 			if (IsItemClickEnabled)
 			{
@@ -849,15 +851,5 @@ private async Task LoadMoreItemsAsync(object incrementalSource, uint count)
 				TryLoadMoreItems();
 			}
 		}
-
-		/// <summary>
-		/// Is the ListView.managed implementation used on this platform?
-		/// </summary>
-		internal static bool UsesManagedLayouting =>
-#if __IOS__ || __ANDROID__
-			false;
-#else
-			true;
-#endif
 	}
 }

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.managed.cs

@@ -13,20 +13,6 @@ public partial class ListViewBase
 	{
 		private int PageSize => throw new NotImplementedException();
 
-		private protected override bool ShouldItemsControlManageChildren => !(ItemsPanelRoot is IVirtualizingPanel);
-
-		private protected override void Refresh()
-		{
-			base.Refresh();
-
-			if (VirtualizingPanel != null)
-			{
-				VirtualizingPanel.GetLayouter().Refresh();
-
-				InvalidateMeasure();
-			}
-		}
-
 		private void AddItems(int firstItem, int count, int section)
 		{
 			if (VirtualizingPanel != null)

src/Uno.UI/UI/Xaml/Controls/ListViewBase/VirtualizingPanelLayout.cs

@@ -83,19 +83,20 @@ internal SnapPointsType SnapPointsType
 		{
 			get
 			{
-				if (XamlParent == null)
+				var parentList = XamlParent as ListViewBase;
+				if (parentList == null)
 				{
 					return default;
 				}
 
 				if (ScrollOrientation == Orientation.Vertical)
 				{
-					return XamlParent.ScrollViewer.VerticalSnapPointsType;
+					return parentList.ScrollViewer.VerticalSnapPointsType;
 				}
 
 				else
 				{
-					return XamlParent.ScrollViewer.HorizontalSnapPointsType;
+					return parentList.ScrollViewer.HorizontalSnapPointsType;
 				}
 			}
 		}
@@ -104,19 +105,20 @@ internal SnapPointsAlignment SnapPointsAlignment
 		{
 			get
 			{
-				if (XamlParent == null)
+				var parentList = XamlParent as ListViewBase;
+				if (parentList == null)
 				{
 					return default;
 				}
 
 				if (ScrollOrientation == Orientation.Vertical)
 				{
-					return XamlParent.ScrollViewer.VerticalSnapPointsAlignment;
+					return parentList.ScrollViewer.VerticalSnapPointsAlignment;
 				}
 
 				else
 				{
-					return XamlParent.ScrollViewer.HorizontalSnapPointsAlignment;
+					return parentList.ScrollViewer.HorizontalSnapPointsAlignment;
 				}
 			}
 		}

src/Uno.UI/UI/Xaml/Controls/ListViewBase/VirtualizingPanelLayout.managed.cs

@@ -51,7 +51,7 @@ private protected VirtualizingPanelGenerator Generator
 
 		private ScrollViewer? ScrollViewer { get; set; }
 		internal ItemsControl? ItemsControl { get; set; }
-		public ListViewBase? XamlParent => ItemsControl as ListViewBase;
+		public ItemsControl? XamlParent => ItemsControl;
 
 		/// <summary>
 		/// Ordered record of all currently-materialized lines.
@@ -749,7 +749,7 @@ private void ScrapLayout()
 		/// </summary>
 		protected virtual Uno.UI.IndexPath? GetDynamicSeedIndex(Uno.UI.IndexPath? firstVisibleItem)
 		{
-			var lastItem = XamlParent?.GetLastItem();
+			var lastItem = ItemsControl?.GetLastItem();
 			if (lastItem == null ||
 				(firstVisibleItem != null && firstVisibleItem.Value > lastItem.Value)
 			)
@@ -1041,7 +1041,7 @@ protected bool ShouldInsertReorderingView(double extentOffset)
 			{
 				if (reorder.index is null)
 				{
-					reorder.index = XamlParent!.GetIndexPathFromItem(reorder.item);
+					reorder.index = ItemsControl!.GetIndexPathFromItem(reorder.item);
 					_pendingReorder = reorder; // _pendingReorder is a struct!
 				}
 

src/Uno.UI/UI/Xaml/Controls/Primitives/Selector.cs

@@ -503,7 +503,19 @@ internal override void OnItemsSourceGroupsChanged(object sender, NotifyCollectio
 
 		internal void OnItemClicked(SelectorItem selectorItem) => OnItemClicked(IndexFromContainer(selectorItem));
 
-		internal virtual void OnItemClicked(int clickedIndex) { }
+		internal virtual void OnItemClicked(int clickedIndex)
+		{
+			if (ItemsSource is ICollectionView collectionView)
+			{
+				//NOTE: Windows seems to call MoveCurrentTo(item); we set position instead to have expected behavior when you have duplicate items in the list.
+				collectionView.MoveCurrentToPosition(clickedIndex);
+
+				// The CollectionView may have intercepted the change
+				clickedIndex = collectionView.CurrentPosition;
+			}
+
+			SelectedIndex = clickedIndex;
+		}
 
 		protected override void OnItemsChanged(object e)
 		{
@@ -611,6 +623,7 @@ private protected override void Refresh()
 		{
 			base.Refresh();
 			_itemTemplatesThatArentContainers.Clear();
+			RefreshPartial();
 		}
 
 
@@ -776,5 +789,18 @@ bool CanScrollIntoView()
 
 			return !isItemsHostInvalid && isInLiveTree && !m_skipScrollIntoView && !m_inCollectionChange;
 		}
+
+		partial void RefreshPartial();
+
+
+		/// <summary>
+		/// Is the ListView.managed implementation used on this platform?
+		/// </summary>
+		internal const bool UsesManagedLayouting =
+#if __IOS__ || __ANDROID__
+			false;
+#else
+			true;
+#endif
 	}
 }

src/Uno.UI/UI/Xaml/Controls/Primitives/Selector.managed.cs

@@ -0,0 +1,37 @@
+#if UNO_REFERENCE_API || __MACOS__
+using Uno.UI.Controls;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Uno.Extensions;
+using System.Collections.Specialized;
+using Uno.Extensions.Specialized;
+using System.Diagnostics;
+using Uno.UI;
+using Uno.Disposables;
+using Windows.UI.Xaml.Data;
+using Uno.UI.DataBinding;
+using Windows.Foundation.Collections;
+
+namespace Windows.UI.Xaml.Controls.Primitives
+{
+	partial class Selector
+	{
+		private protected IVirtualizingPanel VirtualizingPanel => ItemsPanelRoot as IVirtualizingPanel;
+
+		private protected override bool ShouldItemsControlManageChildren => !(ItemsPanelRoot is IVirtualizingPanel);
+
+		partial void RefreshPartial()
+		{
+			if (VirtualizingPanel != null)
+			{
+				VirtualizingPanel.GetLayouter().Refresh();
+
+				InvalidateMeasure();
+			}
+		}
+	}
+}
+#endif