Use better logical child tracking

For now there are internal methods we can call for adding/removing logical children without having to maintain a list ourselves.  This moves the logic out into extension methods which currently uses reflection to get either the internal method, or if that's not found, on newer .NET 8 previews/rc's the method is public so we can safeguard to get that via reflection until a newer sdk is released where we can compile against the upcoming change.

VirtualListView/Controls/ViewExtensions.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Reflection;
+
+namespace Microsoft.Maui.Controls;
+
+internal static class ViewExtensions
+{
+	static PropertyInfo DataTemplateIdPropertyInfo;
+
+	internal static string GetDataTemplateId(this DataTemplate dataTemplate)
+	{
+		DataTemplateIdPropertyInfo ??= dataTemplate.GetType().GetProperty("Id", BindingFlags.Instance | BindingFlags.NonPublic);
+
+		return DataTemplateIdPropertyInfo.GetValue(dataTemplate)?.ToString();
+
+	}
+
+	static MethodInfo removeLogicalChildMethod = null;
+
+	internal static void RemoveLogicalChild(this Element parent, IView view)
+	{
+		if (view is Element elem)
+		{
+			removeLogicalChildMethod ??= GetLogicalChildMethod(parent, "RemoveLogicalChildInternal", "RemoveLogicalChild");
+			removeLogicalChildMethod?.Invoke(parent, new[] { elem });
+		}
+	}
+
+	static MethodInfo addLogicalChildMethod = null;
+
+	internal static void AddLogicalChild(this Element parent, IView view)
+	{
+		if (view is Element elem)
+		{
+			addLogicalChildMethod ??= GetLogicalChildMethod(parent, "AddLogicalChildInternal", "AddLogicalChild");
+			addLogicalChildMethod?.Invoke(parent, new[] { elem });
+		}
+	}
+
+	static MethodInfo GetLogicalChildMethod(Element parent, string internalName, string publicName)
+	{
+		var internalMethod = parent.GetType().GetMethod(
+				internalName,
+				BindingFlags.Instance | BindingFlags.NonPublic,
+				new[] { typeof(Element) });
+
+		if (internalMethod is null)
+		{
+			internalMethod = parent.GetType().GetMethod(
+				publicName,
+				BindingFlags.Instance | BindingFlags.Public,
+				new[] { typeof(Element) });
+		}
+
+		return internalMethod;
+	}
+}
+

VirtualListView/Controls/VirtualListView.cs

@@ -1,16 +1,10 @@
-using Microsoft.Maui.Adapters;
-using System.Reflection;
-using System.Windows.Input;
-
+using System.Windows.Input;
+using Microsoft.Maui.Adapters;
+
 namespace Microsoft.Maui.Controls;
 
 public partial class VirtualListView : View, IVirtualListView, IVirtualListViewSelector, IVisualTreeElement
 {
-	static VirtualListView()
-	{
-
-	}
-
 	public static readonly BindableProperty PositionInfoProperty = BindableProperty.CreateAttached(
 		nameof(PositionInfo),
 		typeof(PositionInfo),
@@ -165,10 +159,48 @@ public View EmptyView
 	}
 
 	public static readonly BindableProperty EmptyViewProperty =
-		BindableProperty.Create(nameof(EmptyView), typeof(View), typeof(VirtualListView), null);
+		BindableProperty.Create(nameof(EmptyView), typeof(View), typeof(VirtualListView), null,
+			propertyChanged: (bobj, oldValue, newValue) =>
+			{
+				if (bobj is VirtualListView virtualListView)
+				{
+					if (oldValue is IView oldView)
+						virtualListView.RemoveLogicalChild(oldView);
+
+					if (newValue is IView newView)
+						virtualListView.AddLogicalChild(newView);
+				}
+			});
 
 	IView IVirtualListView.EmptyView => EmptyView;
 
+
+
+	public View RefreshView
+	{
+		get => (View)GetValue(RefreshViewProperty);
+		set => SetValue(RefreshViewProperty, value);
+	}
+
+	public static readonly BindableProperty RefreshViewProperty =
+		BindableProperty.Create(nameof(EmptyView), typeof(View), typeof(VirtualListView), null,
+			propertyChanged: (bobj, oldValue, newValue) =>
+			{
+				if (bobj is VirtualListView virtualListView)
+				{
+					if (oldValue is IView oldView)
+						virtualListView.RemoveLogicalChild(oldView);
+
+					if (newValue is IView newView)
+						virtualListView.AddLogicalChild(newView);
+				}
+			});
+
+	IView IVirtualListView.RefreshView => RefreshView;
+
+
+
+
 	public IVirtualListViewSelector ViewSelector => this;
 
 	public IView Header => GlobalHeader;
@@ -245,89 +277,29 @@ public string GetReuseId(PositionInfo position, object data)
 		=> position.Kind switch
 		{
 			PositionKind.Item =>
-				"ITEM_" + (GetDataTemplateId(
-					ItemTemplateSelector?.SelectTemplate(data, position.SectionIndex, position.ItemIndex)
-					?? ItemTemplate) ?? "0"),
+				"ITEM_" +
+					(ItemTemplateSelector?.SelectTemplate(data, position.SectionIndex, position.ItemIndex)
+						?? ItemTemplate)?.GetDataTemplateId() ?? "0",
 			PositionKind.SectionHeader =>
-				"SECTION_HEADER_" + (GetDataTemplateId(
-					SectionHeaderTemplateSelector?.SelectTemplate(data, position.SectionIndex)
-					?? SectionHeaderTemplate) ?? "0"),
+				"SECTION_HEADER_" +
+					(SectionHeaderTemplateSelector?.SelectTemplate(data, position.SectionIndex)
+						?? SectionHeaderTemplate)?.GetDataTemplateId() ?? "0",
 			PositionKind.SectionFooter =>
-				"SECTION_FOOTER_" + (GetDataTemplateId(
-					SectionFooterTemplateSelector?.SelectTemplate(data, position.SectionIndex)
-					?? SectionFooterTemplate) ?? "0"),
+				"SECTION_FOOTER_" +
+					(SectionFooterTemplateSelector?.SelectTemplate(data, position.SectionIndex)
+						?? SectionFooterTemplate)?.GetDataTemplateId() ?? "0",
 			PositionKind.Header =>
 				"GLOBAL_HEADER_" + (Header?.GetType()?.FullName ?? "NIL"),
 			PositionKind.Footer =>
 				"GLOBAL_FOOTER_" + (Footer?.GetType()?.FullName ?? "NIL"),
 			_ => "UNKNOWN"
 		};
 
-	static PropertyInfo DataTemplateIdPropertyInfo;
-
-	string? GetDataTemplateId(DataTemplate dataTemplate)
-	{
-		DataTemplateIdPropertyInfo ??= dataTemplate.GetType().GetProperty("Id", BindingFlags.Instance | BindingFlags.NonPublic);
-
-		return DataTemplateIdPropertyInfo.GetValue(dataTemplate)?.ToString();
-
-	}
-
-	public IReadOnlyList<IVisualTreeElement> GetVisualChildren()
-	{
-		var results = new List<IVisualTreeElement>();
-
-		foreach (var c in logicalChildren)
-		{
-			if (c.view is IVisualTreeElement vte)
-				results.Add(vte);
-		}
-
-		return results;
-	}
-
-	readonly object lockLogicalChildren = new();
-	readonly List<(int section, int item, Element view)> logicalChildren = new();
-
 	public void ViewDetached(PositionInfo position, IView view)
-	{
-		var oldLogicalIndex = -1;
-		lock (lockLogicalChildren)
-		{
-			Element elem= null;
-
-			for (var i = 0; i < logicalChildren.Count; i++)
-			{
-				var child = logicalChildren[i];
-
-				if (child.section == position.SectionIndex
-					&& child.item == position.ItemIndex)
-				{
-					elem = child.view;
-					oldLogicalIndex = i;
-					break;
-				}
-			}
-
-			if (oldLogicalIndex >= 0)
-			{
-				logicalChildren.RemoveAt(oldLogicalIndex);
-				if (elem != null)
-					VisualDiagnostics.OnChildRemoved(this, elem, oldLogicalIndex);
-			}
-		}
-	}
+		=> this.RemoveLogicalChild(view);
 
 	public void ViewAttached(PositionInfo position, IView view)
-	{
-		if (view is Element elem)
-		{
-			lock (lockLogicalChildren)
-				logicalChildren.Add((position.SectionIndex, position.ItemIndex, elem));
-
-			VisualDiagnostics.OnChildAdded(this, elem);
-		}
-	}
+		=> this.AddLogicalChild(view);
 
 	public bool IsItemSelected(int sectionIndex, int itemIndex)
 		=> (Handler as VirtualListViewHandler).IsItemSelected(sectionIndex, itemIndex);

VirtualListView/IVirtualListView.cs

@@ -31,6 +31,8 @@ public interface IVirtualListView : IView
 
 	IView EmptyView { get; }
 
+	IView RefreshView { get; }
+
 	bool IsItemSelected(int sectionIndex, int itemIndex);
 
 	void SelectItems(params ItemPosition[] paths);