[release/8.0.1xx-sr10] Revert PR #23052 behavior under new app contex…

…t switch (#25677)

* Revert PR #23052 behavior under new Microsoft.Maui.UseLegacyMeasureInvalidatedBehavior app context switch

* Align the switch name with .NET 9 switches

---------

Co-authored-by: Filip Navara <[email protected]>

src/Controls/src/Core/LegacyLayouts/Layout.cs

@@ -609,6 +609,11 @@ void OnInternalAdded(View view)
 			{
 				InvalidateLayout();
 			}
+
+			if (UseLegacyMeasureInvalidatedBehaviorEnabled)
+			{
+				view.MeasureInvalidated += OnChildMeasureInvalidated;
+			}
 		}
 
 		void OnInternalRemoved(View view, int oldIndex)
@@ -618,6 +623,11 @@ void OnInternalRemoved(View view, int oldIndex)
 			{
 				InvalidateLayout();
 			}
+
+			if (UseLegacyMeasureInvalidatedBehaviorEnabled)
+			{
+				view.MeasureInvalidated -= OnChildMeasureInvalidated;
+			}
 		}
 
 		bool ShouldLayoutChildren()

src/Controls/src/Core/Page/Page.cs

@@ -66,6 +66,7 @@ public partial class Page : VisualElement, ILayout, IPageController, IElementCon
 
 		readonly Lazy<PlatformConfigurationRegistry<Page>> _platformConfigurationRegistry;
 
+		bool _allocatedFlag;
 		Rect _containerArea;
 
 		bool _containerAreaSet;
@@ -542,6 +543,7 @@ protected override void OnParentSet()
 		/// <param name="height">The height allocated to the page.</param>
 		protected override void OnSizeAllocated(double width, double height)
 		{
+			_allocatedFlag = true;
 			base.OnSizeAllocated(width, height);
 			UpdateChildrenLayout();
 		}
@@ -603,7 +605,12 @@ internal virtual void OnChildMeasureInvalidated(VisualElement child, Invalidatio
 				}
 			}
 
+			_allocatedFlag = false;
 			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+			if (!_allocatedFlag && Width >= 0 && Height >= 0 && UseLegacyMeasureInvalidatedBehaviorEnabled)
+			{
+				SizeAllocated(Width, Height);
+			}
 		}
 
 		internal void OnAppearing(Action action)
@@ -705,6 +712,13 @@ void InternalChildrenOnCollectionChanged(object sender, NotifyCollectionChangedE
 				for (var i = 0; i < e.OldItems.Count; i++)
 				{
 					var item = (Element)e.OldItems[i];
+
+					if (UseLegacyMeasureInvalidatedBehaviorEnabled &&
+						item is VisualElement visual)
+					{
+						visual.MeasureInvalidated -= OnChildMeasureInvalidated;
+					}
+
 					RemoveLogicalChild(item);
 				}
 			}
@@ -721,6 +735,12 @@ void InternalChildrenOnCollectionChanged(object sender, NotifyCollectionChangedE
 						insertIndex = InternalChildren.IndexOf(item);
 					}
 
+					if (UseLegacyMeasureInvalidatedBehaviorEnabled &&
+						item is VisualElement visual)
+					{
+						visual.MeasureInvalidated += OnChildMeasureInvalidated;
+					}
+
 					InsertLogicalChild(insertIndex, item);
 
 					if (item is VisualElement)

src/Controls/src/Core/VisualElement/VisualElement.cs

@@ -1345,6 +1345,13 @@ internal void InvokeFocusChangeRequested(FocusRequestArgs args) =>
 			FocusChangeRequested?.Invoke(this, args);
 		internal bool HasFocusChangeRequestedEvent => FocusChangeRequested is not null;
 
+		// Reverts the behavior changed in https://github.com/dotnet/maui/pull/23052/. This unblock customers that
+		// rely on the previous behavior or that are affected by the event propagation being slow on deep control
+		// hierarchies. This can be removed once a better fix is in place, such as https://github.com/dotnet/maui/pull/24848
+		// or https://github.com/dotnet/maui/pull/25291.
+		internal static bool UseLegacyMeasureInvalidatedBehaviorEnabled { get; } =
+			AppContext.TryGetSwitch("Microsoft.Maui.RuntimeFeature.UseLegacyMeasureInvalidatedBehavior", out var enabled) && enabled;
+
 		/// <summary>
 		/// Invalidates the measure of an element.
 		/// </summary>
@@ -1375,7 +1382,10 @@ internal virtual void InvalidateMeasureInternal(InvalidationTrigger trigger)
 			}
 
 			MeasureInvalidated?.Invoke(this, new InvalidationEventArgs(trigger));
-			(Parent as VisualElement)?.OnChildMeasureInvalidatedInternal(this, trigger);
+			if (!UseLegacyMeasureInvalidatedBehaviorEnabled)
+			{
+				(Parent as VisualElement)?.OnChildMeasureInvalidatedInternal(this, trigger);
+			}
 		}
 
 		internal virtual void OnChildMeasureInvalidatedInternal(VisualElement child, InvalidationTrigger trigger)