[Perf] Lazy-initialize _triggerSpecificity dictionary on BindableObject

src/Controls/src/Core/BindableObject.cs

@@ -38,7 +38,7 @@ public BindableObject()
 		}
 
 		internal ushort _triggerCount = 0;
-		internal Dictionary<TriggerBase, SetterSpecificity> _triggerSpecificity = new Dictionary<TriggerBase, SetterSpecificity>();
+		internal Dictionary<TriggerBase, SetterSpecificity> _triggerSpecificity;
 		readonly Dictionary<BindableProperty, BindablePropertyContext> _properties = new Dictionary<BindableProperty, BindablePropertyContext>(4);
 		bool _applying;
 		WeakReference _inheritedContext;

src/Controls/src/Core/Interactivity/TriggerBase.cs

@@ -90,6 +90,7 @@ internal virtual void OnAttachedTo(BindableObject bindable)
 				var manualSpecificity = (ushort)(SetterSpecificity.ManualTriggerBaseline + triggerIndex);
 				var specificity = new SetterSpecificity(0, manualSpecificity, 0, 0, 0, 0, 0, 0);
 
+				bindable._triggerSpecificity ??= new Dictionary<TriggerBase, SetterSpecificity>();
 				bindable._triggerSpecificity[this] = specificity;
 				Condition.SetUp(bindable);
 			}
@@ -100,7 +101,7 @@ internal virtual void OnDetachingFrom(BindableObject bindable)
 			if (Condition != null)
 			{
 				Condition.TearDown(bindable);
-				bindable._triggerSpecificity.Remove(this);
+				bindable._triggerSpecificity?.Remove(this);
 			}
 		}
 
@@ -116,7 +117,7 @@ internal virtual void OnSeal()
 
 		void OnConditionChanged(BindableObject bindable, bool oldValue, bool newValue)
 		{
-			if (!bindable._triggerSpecificity.TryGetValue(this, out var specificity))
+			if (bindable._triggerSpecificity?.TryGetValue(this, out var specificity) != true)
 			{
 				// this should never happen
 				return;

src/Core/tests/Benchmarks/Benchmarks/BindableObjectAllocBenchmarker.cs

@@ -0,0 +1,192 @@
+using BenchmarkDotNet.Attributes;
+using Microsoft.Maui.Controls;
+
+namespace Microsoft.Maui.Handlers.Benchmarks
+{
+	[MemoryDiagnoser]
+	public class BindableObjectAllocBenchmarker
+	{
+		// --- #34092: Cached PropertyChangedEventArgs / PropertyChangingEventArgs ---
+
+		/// <summary>
+		/// Sets the same property repeatedly to measure PropertyChanged/Changing EventArgs allocations.
+		/// Before: new PropertyChangedEventArgs + new PropertyChangingEventArgs per call.
+		/// After: cached per BindableProperty.
+		/// </summary>
+		[Benchmark]
+		public void SetProperty_EventArgsAlloc()
+		{
+			var label = new Label();
+			for (int i = 0; i < 1_000; i++)
+			{
+				label.Text = "a";
+				label.Text = "b";
+			}
+		}
+
+		/// <summary>
+		/// Sets multiple different properties to show caching benefit across properties.
+		/// </summary>
+		[Benchmark]
+		public void SetMultipleProperties_EventArgsAlloc()
+		{
+			var entry = new Entry();
+			for (int i = 0; i < 500; i++)
+			{
+				entry.Text = "a";
+				entry.Placeholder = "p";
+				entry.FontSize = 14 + (i % 3);
+				entry.Text = "b";
+				entry.Placeholder = "q";
+			}
+		}
+
+		// --- #34093: Reuse ElementEventArgs in tree propagation ---
+
+		/// <summary>
+		/// Adds children to a deep hierarchy, triggering DescendantAdded propagation.
+		/// Before: new ElementEventArgs at every tree level.
+		/// After: single ElementEventArgs reused through recursion.
+		/// </summary>
+		[Benchmark]
+		public void AddChildren_DeepTree_ElementEventArgs()
+		{
+			// Build a 10-level deep tree
+			var root = new VerticalStackLayout();
+			var current = root;
+			for (int depth = 0; depth < 10; depth++)
+			{
+				var child = new VerticalStackLayout();
+				current.Add(child);
+				current = child;
+			}
+
+			// Add 100 leaves at the bottom — each fires DescendantAdded 10 levels up
+			for (int i = 0; i < 100; i++)
+			{
+				current.Add(new Label());
+			}
+		}
+
+		/// <summary>
+		/// Removes children from a deep hierarchy, triggering DescendantRemoved propagation.
+		/// </summary>
+		[Benchmark]
+		public void RemoveChildren_DeepTree_ElementEventArgs()
+		{
+			var root = new VerticalStackLayout();
+			var current = root;
+			for (int depth = 0; depth < 10; depth++)
+			{
+				var child = new VerticalStackLayout();
+				current.Add(child);
+				current = child;
+			}
+
+			var labels = new Label[100];
+			for (int i = 0; i < 100; i++)
+			{
+				labels[i] = new Label();
+				current.Add(labels[i]);
+			}
+
+			for (int i = 0; i < 100; i++)
+			{
+				current.Remove(labels[i]);
+			}
+		}
+
+		// --- #34129: BindingContext propagation (WeakReference reuse + .ToArray() elimination) ---
+
+		class SimpleViewModel
+		{
+			public string Name { get; set; } = "Test";
+		}
+
+		/// <summary>
+		/// Sets BindingContext on a flat layout with many children.
+		/// Before: new WeakReference per child + .ToArray() on each child's _properties.
+		/// After: reuse WeakReference.Target + foreach on dictionary directly.
+		/// </summary>
+		[Benchmark]
+		public void SetBindingContext_FlatTree()
+		{
+			var layout = new VerticalStackLayout();
+			for (int i = 0; i < 200; i++)
+			{
+				layout.Add(new Label());
+			}
+
+			var vm = new SimpleViewModel();
+			for (int i = 0; i < 10; i++)
+			{
+				layout.BindingContext = vm;
+				layout.BindingContext = null;
+			}
+		}
+
+		/// <summary>
+		/// Sets BindingContext on a deep tree where children have bindings.
+		/// This is the worst-case hot path: ApplyBindings + WeakReference for every descendant.
+		/// </summary>
+		[Benchmark]
+		public void SetBindingContext_DeepTreeWithBindings()
+		{
+			var root = new VerticalStackLayout();
+			var current = root;
+
+			for (int depth = 0; depth < 5; depth++)
+			{
+				var child = new VerticalStackLayout();
+				current.Add(child);
+				current = child;
+			}
+
+			for (int i = 0; i < 50; i++)
+			{
+				var label = new Label();
+				label.SetBinding(Label.TextProperty, new Binding("Name"));
+				current.Add(label);
+			}
+
+			var vm = new SimpleViewModel();
+			for (int i = 0; i < 20; i++)
+			{
+				root.BindingContext = vm;
+				root.BindingContext = null;
+			}
+		}
+
+		// --- #34131: Lazy _triggerSpecificity dictionary ---
+
+		/// <summary>
+		/// Creates many BindableObjects (Labels) that never use triggers.
+		/// Before: each allocates Dictionary&lt;TriggerBase, SetterSpecificity&gt;.
+		/// After: dictionary is null until first trigger attachment.
+		/// </summary>
+		[Benchmark]
+		public Label[] CreateManyLabels_NoTriggers()
+		{
+			var labels = new Label[1_000];
+			for (int i = 0; i < 1_000; i++)
+			{
+				labels[i] = new Label();
+			}
+			return labels;
+		}
+
+		/// <summary>
+		/// Creates many Entries (more complex BindableObject) without triggers.
+		/// </summary>
+		[Benchmark]
+		public Entry[] CreateManyEntries_NoTriggers()
+		{
+			var entries = new Entry[500];
+			for (int i = 0; i < 500; i++)
+			{
+				entries[i] = new Entry();
+			}
+			return entries;
+		}
+	}
+}