[WinUI] Allocate less when updating gestures (#21450)

* `EnumerableExtensions`: Enable nullable

* Add `EnumerableExtensions.HasAnyGesturesFor`

* Sandbox measure code

* Revert "Sandbox measure code"

This reverts commit e984695.

* Do not create lambdas + apply MSVS suggestion regarding pattern matching + add braces

* Make `HasAnyGesturesFor` `internal`

* Reimplement by adding `FirstGestureOrDefault`

src/Controls/src/Core/EnumerableExtensions.cs

@@ -1,64 +1,86 @@
-#nullable disable
 using System;
 using System.Collections.Generic;
-using System.ComponentModel;
 
 namespace Microsoft.Maui.Controls.Internals
 {
 	static class EnumerableExtensions
 	{
-		public static bool HasChildGesturesFor<T>(this IEnumerable<GestureElement> elements, Func<T, bool> predicate = null) where T : GestureRecognizer
+		public static bool HasChildGesturesFor<T>(this IEnumerable<GestureElement>? elements, Func<T, bool>? predicate = null) where T : GestureRecognizer
 		{
-			if (elements == null)
+			if (elements is null)
+			{
 				return false;
-
-			if (predicate == null)
-				predicate = x => true;
+			}
 
 			foreach (var element in elements)
+			{
 				foreach (var item in element.GestureRecognizers)
 				{
-					var gesture = item as T;
-					if (gesture != null && predicate(gesture))
+					if (item is T gesture && (predicate is null || predicate(gesture)))
+					{
 						return true;
+					}
 				}
+			}
 
 			return false;
 		}
 
-		public static IEnumerable<T> GetChildGesturesFor<T>(this IEnumerable<GestureElement> elements, Func<T, bool> predicate = null) where T : GestureRecognizer
+		public static IEnumerable<T> GetChildGesturesFor<T>(this IEnumerable<GestureElement>? elements, Func<T, bool>? predicate = null) where T : GestureRecognizer
 		{
-			if (elements == null)
+			if (elements is null)
+			{
 				yield break;
-
-			if (predicate == null)
-				predicate = x => true;
+			}
 
 			foreach (var element in elements)
+			{
 				foreach (var item in element.GestureRecognizers)
 				{
-					var gesture = item as T;
-					if (gesture != null && predicate(gesture))
+					if (item is T gesture && (predicate is null || predicate(gesture)))
+					{
 						yield return gesture;
+					}
 				}
+			}
 		}
 
-		public static IEnumerable<T> GetGesturesFor<T>(this IEnumerable<IGestureRecognizer> gestures, Func<T, bool> predicate = null) where T : GestureRecognizer
+		/// <remarks>The method makes a defensive copy of the gestures.</remarks>
+		public static IEnumerable<T> GetGesturesFor<T>(this IEnumerable<IGestureRecognizer>? gestures, Func<T, bool>? predicate = null) where T : GestureRecognizer
 		{
-			if (gestures == null)
+			if (gestures is null)
+			{
 				yield break;
-
-			if (predicate == null)
-				predicate = x => true;
+			}
 
 			foreach (IGestureRecognizer item in new List<IGestureRecognizer>(gestures))
 			{
-				var gesture = item as T;
-				if (gesture != null && predicate(gesture))
+				if (item is T gesture && (predicate is null || predicate(gesture)))
 				{
 					yield return gesture;
 				}
 			}
 		}
+
+		internal static bool HasAnyGesturesFor<T>(this IEnumerable<IGestureRecognizer>? gestures, Func<T, bool>? predicate = null) where T : GestureRecognizer
+			=> FirstGestureOrDefault(gestures, predicate) is not null;
+
+		internal static T? FirstGestureOrDefault<T>(this IEnumerable<IGestureRecognizer>? gestures, Func<T, bool>? predicate = null) where T : GestureRecognizer
+		{
+			if (gestures is null)
+			{
+				return null;
+			}
+
+			foreach (IGestureRecognizer item in gestures)
+			{
+				if (item is T gesture && (predicate is null || predicate(gesture)))
+				{
+					return gesture;
+				}
+			}
+
+			return null;
+		}
 	}
 }

src/Controls/src/Core/Platform/GestureManager/GesturePlatformManager.Windows.cs

@@ -670,28 +670,32 @@ void PinchComplete(bool success)
 
 		void UpdateDragAndDropGestureRecognizers()
 		{
-			if (_container == null)
+			if (_container is null)
+			{
 				return;
+			}
 
 			var view = Element as View;
 			IList<IGestureRecognizer>? gestures = view?.GestureRecognizers;
 
-			if (gestures == null)
+			if (gestures is null)
+			{
 				return;
+			}
 
-			_container.CanDrag = gestures.GetGesturesFor<DragGestureRecognizer>()
-				.FirstOrDefault()?.CanDrag ?? false;
+			bool canDrag = gestures.FirstGestureOrDefault<DragGestureRecognizer>()?.CanDrag ?? false;
+			_container.CanDrag = canDrag;
 
-			_container.AllowDrop = gestures.GetGesturesFor<DropGestureRecognizer>()
-				.FirstOrDefault()?.AllowDrop ?? false;
+			bool allowDrop = gestures.FirstGestureOrDefault<DropGestureRecognizer>()?.AllowDrop ?? false;
+			_container.AllowDrop = allowDrop;
 
-			if (_container.CanDrag)
+			if (canDrag)
 			{
 				_container.DragStarting += HandleDragStarting;
 				_container.DropCompleted += HandleDropCompleted;
 			}
 
-			if (_container.AllowDrop)
+			if (allowDrop)
 			{
 				_container.DragOver += HandleDragOver;
 				_container.Drop += HandleDrop;
@@ -714,7 +718,7 @@ void UpdatingGestureRecognizers()
 			IList<TapGestureRecognizer>? childGestures =
 				children?.GetChildGesturesFor<TapGestureRecognizer>().ToList();
 
-			if (gestures.GetGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1).Any()
+			if (gestures.HasAnyGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1)
 				|| children?.GetChildGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1).Any() == true)
 			{
 				_container.Tapped += OnTap;
@@ -728,7 +732,7 @@ void UpdatingGestureRecognizers()
 				}
 			}
 
-			if (gestures.GetGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1 || g.NumberOfTapsRequired == 2).Any()
+			if (gestures.HasAnyGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1 || g.NumberOfTapsRequired == 2)
 				|| children?.GetChildGesturesFor<TapGestureRecognizer>(g => g.NumberOfTapsRequired == 1 || g.NumberOfTapsRequired == 2).Any() == true)
 			{
 				_container.DoubleTapped += OnTap;
@@ -747,11 +751,13 @@ void UpdatingGestureRecognizers()
 			_container.PointerPressed += OnPgrPointerPressed;
 			_container.PointerReleased += OnPgrPointerReleased;
 
-			bool hasSwipeGesture = gestures.GetGesturesFor<SwipeGestureRecognizer>().GetEnumerator().MoveNext();
-			bool hasPinchGesture = gestures.GetGesturesFor<PinchGestureRecognizer>().GetEnumerator().MoveNext();
-			bool hasPanGesture = gestures.GetGesturesFor<PanGestureRecognizer>().GetEnumerator().MoveNext();
+			bool hasSwipeGesture = gestures.HasAnyGesturesFor<SwipeGestureRecognizer>();
+			bool hasPinchGesture = gestures.HasAnyGesturesFor<PinchGestureRecognizer>();
+			bool hasPanGesture = gestures.HasAnyGesturesFor<PanGestureRecognizer>();
 			if (!hasSwipeGesture && !hasPinchGesture && !hasPanGesture)
+			{
 				return;
+			}
 
 			//We can't handle ManipulationMode.Scale and System , so we don't support pinch/pan on a scrollview 
 			if (Element is ScrollView)