Optimize GetVisualTreeElementsWindowsInternal (#19984)

* add benchmark

* prevent multiple enumerations

---------

Co-authored-by: Edward Miller <symbiogenisis@outlook.com>

src/Core/src/Core/Extensions/VisualTreeElementExtensions.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.Maui.Graphics;
@@ -145,14 +145,27 @@ static List<IVisualTreeElement> GetVisualTreeElementsWindowsInternal(IVisualTree
 
 			if (uiElement != null)
 			{
-				var uniqueElements = findChildren(uiElement).Distinct();
-				var viewTree = visualElement.GetVisualTreeDescendants().Where(n => n is IView view && view.Handler is not null).Select(n => new Tuple<IView, object?>((IView)n, ((IView)n).ToPlatform()));
-				var testList = viewTree.Where(n => uniqueElements.Contains(n.Item2)).Select(n => n.Item1);
-				if (testList != null && testList.Any())
-					visualElements.AddRange(testList.Select(n => (IVisualTreeElement)n));
+				var uniqueElements = findChildren(uiElement).ToHashSet();
+
+				var descendants = visualElement.GetVisualTreeDescendants();
+
+				// Add in reverse order
+				for (int i = descendants.Count - 1; i >= 0; i--)
+				{
+					var descendant = descendants[i];
+
+					if (descendant is not IView view || view.Handler is null)
+					{
+						continue;
+					}
+
+					if (uniqueElements.Contains(view.ToPlatform()))
+					{
+						visualElements.Add(descendant);
+					}
+				}
 			}
 
-			visualElements.Reverse();
 			return visualElements;
 		}
 #endif

src/Core/tests/Benchmarks/Benchmarks/VisualTreeBenchmarker.cs

@@ -0,0 +1,49 @@
+using BenchmarkDotNet.Attributes;
+using Microsoft.Maui.Controls;
+
+namespace Microsoft.Maui.Benchmarks
+{
+	[MemoryDiagnoser]
+	public class VisualTreeBenchmarker
+	{
+		static readonly View[] Views = [
+			new Border(), new BoxView(), new CarouselView(), new Grid(), new Entry(), new Picker(), new CollectionView(),
+			new CheckBox(), new DatePicker(), new Stepper(), new Slider(), new ActivityIndicator(), new Frame(),
+			new ContentView(), new ProgressBar(), new SearchBar(), new Switch(), new TimePicker(), new WebView(), new Button(),
+		];
+
+		private const int Iterations = 100;
+
+		[Benchmark]
+		public void GetVisualTreeElements()
+		{
+			var layout = new VerticalStackLayout();
+
+			for (int i = 0; i < Iterations; i++)
+			{
+				var childLayout = new VerticalStackLayout();
+
+				foreach (var view in Views)
+				{
+					childLayout.Add(view);
+
+					var grandchildLayout = new VerticalStackLayout();
+
+					foreach (var view2 in Views)
+					{
+						grandchildLayout.Add(view);
+						grandchildLayout.GetVisualTreeElements(grandchildLayout.Frame);
+					}
+
+					layout.Add(grandchildLayout);
+
+					childLayout.GetVisualTreeElements(childLayout.Frame);
+				}
+
+				layout.Add(childLayout);
+
+				layout.GetVisualTreeElements(layout.Frame);
+			}
+		}
+	}
+}