Reduce the number of calls to invalidate measure

src/Controls/src/Core/Label/Label.cs

@@ -62,7 +62,8 @@ public partial class Label : View, IFontElement, ITextElement, ITextAlignmentEle
 					formattedString.Parent = null;
 					label.RemoveSpans(formattedString.Spans);
 				}
-			}, propertyChanged: (bindable, oldvalue, newvalue) =>
+			},
+			propertyChanged: (bindable, oldvalue, newvalue) =>
 			{
 				var label = ((Label)bindable);
 
@@ -76,7 +77,8 @@ public partial class Label : View, IFontElement, ITextElement, ITextAlignmentEle
 					label.SetupSpans(formattedString.Spans);
 				}
 
-				label.InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+				label.InvalidateMeasureIfLabelSizeable();
+
 				if (newvalue != null)
 					label.Text = null;
 			});
@@ -94,26 +96,21 @@ public virtual string UpdateFormsText(string source, TextTransform textTransform
 
 		/// <summary>Bindable property for <see cref="LineBreakMode"/>.</summary>
 		public static readonly BindableProperty LineBreakModeProperty = BindableProperty.Create(nameof(LineBreakMode), typeof(LineBreakMode), typeof(Label), LineBreakMode.WordWrap,
-			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged));
+			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureIfLabelSizeable());
 
 		/// <summary>Bindable property for <see cref="LineHeight"/>.</summary>
 		public static readonly BindableProperty LineHeightProperty = LineHeightElement.LineHeightProperty;
 
 		/// <summary>Bindable property for <see cref="MaxLines"/>.</summary>
-		public static readonly BindableProperty MaxLinesProperty = BindableProperty.Create(nameof(MaxLines), typeof(int), typeof(Label), -1, propertyChanged: (bindable, oldvalue, newvalue) =>
-			{
-				if (bindable != null)
-				{
-					((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
-				}
-			});
+		public static readonly BindableProperty MaxLinesProperty = BindableProperty.Create(nameof(MaxLines), typeof(int), typeof(Label), -1,
+			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureIfLabelSizeable());
 
 		/// <summary>Bindable property for <see cref="Padding"/>.</summary>
 		public static readonly BindableProperty PaddingProperty = PaddingElement.PaddingProperty;
 
 		/// <summary>Bindable property for <see cref="TextType"/>.</summary>
 		public static readonly BindableProperty TextTypeProperty = BindableProperty.Create(nameof(TextType), typeof(TextType), typeof(Label), TextType.Text,
-			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged));
+			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureIfLabelSizeable());
 
 		readonly Lazy<PlatformConfigurationRegistry<Label>> _platformConfigurationRegistry;
 
@@ -260,24 +257,22 @@ void IFontElement.OnFontAutoScalingEnabledChanged(bool oldValue, bool newValue)
 		void HandleFontChanged()
 		{
 			Handler?.UpdateValue(nameof(ITextStyle.Font));
-			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+			InvalidateMeasureIfLabelSizeable();
 		}
 
 		void ILineHeightElement.OnLineHeightChanged(double oldValue, double newValue) =>
-			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
-
-		void OnFormattedTextChanging(object sender, PropertyChangingEventArgs e)
-		{
-			OnPropertyChanging(nameof(FormattedText));
-		}
+			InvalidateMeasureIfLabelSizeable();
 
 		void ITextElement.OnTextTransformChanged(TextTransform oldValue, TextTransform newValue) =>
-			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+			InvalidateMeasureIfLabelSizeable();
+
+		void OnFormattedTextChanging(object sender, PropertyChangingEventArgs e) =>
+			OnPropertyChanging(nameof(FormattedText));
 
 		void OnFormattedTextChanged(object sender, PropertyChangedEventArgs e)
 		{
 			OnPropertyChanged(nameof(FormattedText));
-			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+			InvalidateMeasureIfLabelSizeable();
 		}
 
 		void SetupSpans(IEnumerable spans)
@@ -357,18 +352,19 @@ void Span_GestureRecognizer_CollectionChanged(object sender, NotifyCollectionCha
 
 		void ITextAlignmentElement.OnHorizontalTextAlignmentPropertyChanged(TextAlignment oldValue, TextAlignment newValue)
 		{
+			// This is a no-op since the horizontal text alignment does not affect bounds or
+			// any other property that would require a measure invalidation.
 		}
 
 		static void OnTextPropertyChanged(BindableObject bindable, object oldvalue, object newvalue)
 		{
 			var label = (Label)bindable;
-			LineBreakMode breakMode = label.LineBreakMode;
-			bool isVerticallyFixed = (label.Constraint & LayoutConstraint.VerticallyFixed) != 0;
-			bool isSingleLine = !(breakMode == LineBreakMode.CharacterWrap || breakMode == LineBreakMode.WordWrap);
-			if (!isVerticallyFixed || !isSingleLine)
-				((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+
+			if (TextChangedShouldInvalidateMeasure(label))
+				label.InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
+
 			if (newvalue != null)
-				((Label)bindable).FormattedText = null;
+				label.FormattedText = null;
 		}
 
 		/// <inheritdoc/>
@@ -379,12 +375,12 @@ public IPlatformElementConfiguration<T, Label> On<T>() where T : IConfigPlatform
 
 		void ITextElement.OnTextColorPropertyChanged(Color oldValue, Color newValue)
 		{
+			// This is a no-op since the text color does not affect bounds or
+			// any other property that would require a measure invalidation.
 		}
 
-		void ITextElement.OnCharacterSpacingPropertyChanged(double oldValue, double newValue)
-		{
-			InvalidateMeasure();
-		}
+		void ITextElement.OnCharacterSpacingPropertyChanged(double oldValue, double newValue) =>
+			InvalidateMeasureIfLabelSizeable();
 
 		internal bool HasFormattedTextSpans
 			=> (FormattedText?.Spans?.Count ?? 0) > 0;
@@ -411,16 +407,75 @@ public override IList<GestureElement> GetChildElements(Point point)
 			return spans;
 		}
 
-		Thickness IPaddingElement.PaddingDefaultValueCreator()
-		{
-			return default(Thickness);
-		}
+		Thickness IPaddingElement.PaddingDefaultValueCreator() => default;
+
+		void IPaddingElement.OnPaddingPropertyChanged(Thickness oldValue, Thickness newValue) =>
+			InvalidateMeasureIfLabelSizeable();
+
+		Font ITextStyle.Font => this.ToFont();
 
-		void IPaddingElement.OnPaddingPropertyChanged(Thickness oldValue, Thickness newValue)
+		/// <summary>
+		/// This method prevents unnecessary measure invalidations when the label is not
+		/// sizeable. If the label has a fixed width and height, then no matter what the
+		/// text is, the label will never change size.
+		/// </summary>
+		void InvalidateMeasureIfLabelSizeable()
 		{
+			if (!IsLabelSizeable(this))
+				return;
+
 			InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
 		}
 
-		Font ITextStyle.Font => this.ToFont();
+		/// <summary>
+		/// Determines if the label can grow in any direction based on the constraints. If the
+		/// label cannot grow in any direction, then we usually don't need to do anything.
+		/// </summary>
+		internal static bool IsLabelSizeable(Label label)
+		{
+			// Determine in which direction the label can grow/shrink.
+			var constraint = label.Constraint;
+			var isVerticallySizeable = (constraint & LayoutConstraint.VerticallyFixed) == 0;
+			var isHorizontallySizeable = (constraint & LayoutConstraint.HorizontallyFixed) == 0;
+			var isSizeable = isVerticallySizeable || isHorizontallySizeable;
+
+			// If the label cannot grow in any direction, then we usually don't need to do anything.
+			if (!isSizeable)
+				return false;
+
+			// The label may grow/shrink based on the constraints, so we may need to invalidate.
+			return true;
+		}
+
+		/// <summary>
+		/// Determines if the text has changed in a way that would require a measure invalidation.
+		/// Unlike FormattedText changes, Text changes may not always require invalidation because
+		/// the text size and spacing is all uniform. Formatted text may have a case where even
+		/// though the label is a single line, the font size of a span may cause the label to grow
+		/// vertically.
+		/// </summary>
+		internal static bool TextChangedShouldInvalidateMeasure(Label label)
+		{
+			// If the label cannot grow in any direction, then we don't need to invalidate.
+			var isSizeable = IsLabelSizeable(label);
+			if (!isSizeable)
+				return false;
+
+			// Determine if the label can grow vertically (wrapping means it may grow vertically).
+			var constraint = label.Constraint;
+			var breakMode = label.LineBreakMode;
+			var isHorizontallySizeable = (constraint & LayoutConstraint.HorizontallyFixed) == 0;
+			var isMultiline = breakMode == LineBreakMode.CharacterWrap || breakMode == LineBreakMode.WordWrap;
+			var isSingleLine = !isMultiline;
+
+			// If the label cannot grow horizontally and is only single line,
+			// then we don't need to invalidate since the only direction it can grow in
+			// is vertically but it never will.
+			if (!isHorizontallySizeable && isSingleLine)
+				return false;
+
+			// The label may grow/shrink based on the constraints, so we need to invalidate.
+			return true;
+		}
 	}
 }

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

@@ -1628,11 +1628,11 @@ static void OnRequestChanged(BindableObject bindable, object oldvalue, object ne
 		{
 			var constraint = LayoutConstraint.None;
 			var element = (VisualElement)bindable;
-			if (element.WidthRequest >= 0 && element.MinimumWidthRequest >= 0)
+			if (element.WidthRequest >= 0)
 			{
 				constraint |= LayoutConstraint.HorizontallyFixed;
 			}
-			if (element.HeightRequest >= 0 && element.MinimumHeightRequest >= 0)
+			if (element.HeightRequest >= 0)
 			{
 				constraint |= LayoutConstraint.VerticallyFixed;
 			}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/ReduceInvalidateMeasure.cs

@@ -0,0 +1,57 @@
+#if IOS
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+    internal class ReduceInvalidateMeasure : _IssuesUITest
+	{
+		public ReduceInvalidateMeasure(TestDevice device)
+			: base(device)
+		{ }
+
+		public override string Issue => "https://github.com/dotnet/maui/pull/21801";
+
+		[Test]
+		public void ReduceInvalidateMeasuresUpdatingLabel()
+		{
+			App.WaitForElement("UpdateTextLabel");
+
+			const int repeats = 2;
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateTextButton");
+			}
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateSizeButton");
+			}
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateFontSizeButton");
+			}
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateLineBreakModeButton");
+			}
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateLineHeightButton");
+			}
+
+			for (int i = 0; i < repeats; i++)
+			{
+				App.Tap("UpdateVisibilityButton");
+			}
+
+			VerifyScreenshot();
+		}
+	}
+}
+#endif

src/Controls/tests/TestCases/Issues/ReduceInvalidateMeasure.xaml

@@ -0,0 +1,75 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.ReduceInvalidateMeasure">
+  <ScrollView>
+    <VerticalStackLayout
+      Padding="12">
+      <Label 
+        x:Name="UpdateTextLabel"
+        AutomationId="UpdateTextLabel"
+        BackgroundColor="Red"
+        Text="Lorem ipsum dolor sit amet"/>
+      <Button 
+        x:Name="UpdateTextButton"
+        AutomationId="UpdateTextButton"
+        Text="Update Text"
+        Clicked="OnUpdateTextButtonClicked"/>
+      <Label 
+        x:Name="UpdateSizeLabel"
+        AutomationId="UpdateSizeLabel"
+        BackgroundColor="Blue"
+        Text="Lorem ipsum dolor"
+        HorizontalOptions="Start"
+        WidthRequest="200"/>
+      <Button 
+        x:Name="UpdateSizeButton"
+        AutomationId="UpdateSizeButton"
+        Text="Update Label Size"
+        Clicked="OnUpdateSizeButtonClicked"/>
+      <Label 
+        x:Name="UpdateFontSizeLabel"
+        AutomationId="UpdateFontSizeLabel"
+        TextColor="Green"
+        FontSize="16"
+        Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit"/>
+      <Button 
+        x:Name="UpdateFontSizeButton"
+        AutomationId="UpdateFontSizeButton"
+        Text="Update Label FontSize"
+        Clicked="OnUpdateFontSizeButtonClicked"/>
+      <Label 
+        x:Name="UpdateLineBreakModeLabel"
+        AutomationId="UpdateLineBreakModeLabel"
+        Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit."
+        LineBreakMode="WordWrap"/>
+      <Button 
+        x:Name="UpdateLineBreakModeButton"
+        AutomationId="UpdateLineBreakModeButton"
+        Text="Update Label LineBreakMode"
+        Clicked="OnUpdateLineBreakModeButtonClicked"/>
+      <Label 
+        x:Name="UpdateLineHeightLabel"
+        AutomationId="UpdateLineHeightLabel"
+        LineHeight="1"
+        Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Lorem ipsum dolor sit amet, consectetur adipiscing elit."/>
+      <Button 
+        x:Name="UpdateLineHeightButton"
+        AutomationId="UpdateLineHeightButton"
+        Text="Update Label LineHeight"
+        Clicked="OnUpdateLineHeightButtonClicked"/>
+      <Label 
+        x:Name="UpdateVisibilityLabel"
+        AutomationId="UpdateVisibilityLabel"
+        FontSize="Medium"
+        TextColor="Orange"
+        Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit."
+        LineBreakMode="WordWrap"/>
+      <Button 
+        x:Name="UpdateVisibilityButton"
+        AutomationId="UpdateVisibilityButton"
+        Text="Update Label Visibility"
+        Clicked="OnUpdateVisibilityButtonClicked"/>
+    </VerticalStackLayout>
+  </ScrollView>
+</ContentPage>