perf: Make VisualState and VisualTransition lazy loaded

Setting `UnoXamlLazyVisualStateManagerEnabled` to false as an msbuild property disables the feature.

src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlCodeGeneration.cs

@@ -54,6 +54,11 @@ internal partial class XamlCodeGeneration
 		/// </summary>
 		private readonly bool _shouldAnnotateGeneratedXaml = false;
 
+		/// <summary>
+		/// When set, Visual State Manager children will be initialized lazily for performance
+		/// </summary>
+		private readonly bool _isLazyVisualStateManagerEnabled = true;
+
 		private static DateTime _buildTasksBuildDate = File.GetLastWriteTime(new Uri(typeof(XamlFileGenerator).Assembly.Location).LocalPath);
 		private INamedTypeSymbol[]? _ambientGlobalResources;
 		private readonly bool _isUiAutomationMappingEnabled;
@@ -157,6 +162,11 @@ public XamlCodeGeneration(GeneratorExecutionContext context)
 				_shouldAnnotateGeneratedXaml = shouldAnnotateGeneratedXaml;
 			}
 
+			if (bool.TryParse(context.GetMSBuildPropertyValue("UnoXamlLazyVisualStateManagerEnabled"), out var isLazyVisualStateManagerEnabled))
+			{
+				_isLazyVisualStateManagerEnabled = isLazyVisualStateManagerEnabled;
+			}
+
 			_targetPath = Path.Combine(
 				_projectDirectory,
 				context.GetMSBuildPropertyValue("IntermediateOutputPath")
@@ -286,7 +296,8 @@ public KeyValuePair<string, string>[] Generate()
 									isDebug: _isDebug,
 									skipUserControlsInVisualTree: _skipUserControlsInVisualTree,
 									shouldAnnotateGeneratedXaml: _shouldAnnotateGeneratedXaml,
-									isUnoAssembly: IsUnoAssembly
+									isUnoAssembly: IsUnoAssembly,
+									isLazyVisualStateManagerEnabled: _isLazyVisualStateManagerEnabled
 								)
 								.GenerateFile()
 						)

src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.cs

@@ -80,6 +80,11 @@ internal partial class XamlFileGenerator
 		/// </summary>
 		private bool _isTopLevelDictionary;
 		private readonly bool _isUnoAssembly;
+
+		/// <summary>
+		/// True if VisualStateManager children can be set lazily
+		/// </summary>
+		private readonly bool _isLazyVisualStateManagerEnabled;
 		/// <summary>
 		/// True if the generator is currently creating child subclasses (for templates, etc)
 		/// </summary>
@@ -191,7 +196,8 @@ public XamlFileGenerator(
 			bool isDebug,
 			bool skipUserControlsInVisualTree,
 			bool shouldAnnotateGeneratedXaml,
-			bool isUnoAssembly
+			bool isUnoAssembly,
+			bool isLazyVisualStateManagerEnabled
 		)
 		{
 			_fileDefinition = file;
@@ -210,6 +216,7 @@ bool isUnoAssembly
 			_isDebug = isDebug;
 			_skipUserControlsInVisualTree = skipUserControlsInVisualTree;
 			_shouldAnnotateGeneratedXaml = shouldAnnotateGeneratedXaml;
+			_isLazyVisualStateManagerEnabled = isLazyVisualStateManagerEnabled;
 
 			InitCaches();
 
@@ -2185,6 +2192,10 @@ private bool BuildProperties(IIndentedStringBuilder writer, XamlObjectDefinition
 												.InvariantCultureFormat(contentProperty.Name));
 										}
 									}
+									else if (IsLazyVisualStateManagerProperty(contentProperty))
+									{
+										writer.AppendLineInvariant($"/* Lazy VisualStateManager property {contentProperty}*/");
+									}
 									else // Content is not a collection
 									{
 										var objectUid = GetObjectUid(topLevelControl);
@@ -2765,7 +2776,9 @@ private void BuildExtendedProperties(IIndentedStringBuilder outerwriter, XamlObj
 						writer.AppendLine(GenerateRootPhases(objectDefinition, closureName) ?? "");
 					}
 
-					foreach (var member in extendedProperties)
+					var lazyProperties = extendedProperties.Where(IsLazyVisualStateManagerProperty).ToArray();
+
+					foreach (var member in extendedProperties.Except(lazyProperties))
 					{
 						if (extractionTargetMembers != null)
 						{
@@ -3065,6 +3078,35 @@ private void BuildExtendedProperties(IIndentedStringBuilder outerwriter, XamlObj
 						}
 					}
 
+					var implicitContentChild = FindImplicitContentMember(objectDefinition);
+					var lazyContentProperty = FindLazyContentProperty(implicitContentChild, objectDefinition);
+
+					if (lazyProperties.Any() || lazyContentProperty != null)
+					{
+						// This block is used to generate lazy initializations of some
+						// inner VisualStateManager properties in VisualState and VisualTransition.
+						// This allows for faster materialization of controls, avoiding the construction
+						// of inferequently used objects graphs.
+
+						using (writer.BlockInvariant($"global::Uno.UI.Helpers.MarkupHelper.Set{objectDefinition.Type.Name}Lazy({closureName}, () => "))
+						{
+							BuildLiteralLazyVisualStateManagerProperties(writer, objectDefinition, closureName);
+
+							if (implicitContentChild != null && lazyContentProperty != null)
+							{
+								writer.AppendLineInvariant($"{closureName}.{lazyContentProperty.Name} = ");
+
+								var xamlObjectDefinition = implicitContentChild.Objects.First();
+								using (TryAdaptNative(writer, xamlObjectDefinition, lazyContentProperty.Type as INamedTypeSymbol))
+								{
+									BuildChild(writer, implicitContentChild, xamlObjectDefinition);
+								}
+								writer.AppendLineInvariant($";");
+							}
+						}
+						writer.AppendLineInvariant($");");
+					}
+
 					if (HasXBindMarkupExtension(objectDefinition) || HasMarkupExtensionNeedingComponent(objectDefinition))
 					{
 						writer.AppendLineInvariant($"/* _isTopLevelDictionary:{_isTopLevelDictionary} */");
@@ -3134,6 +3176,26 @@ void BuildCustomMarkupExtensionPropertyValue(IIndentedStringBuilder writer, Xaml
 			}
 		}
 
+		private IPropertySymbol? FindLazyContentProperty(XamlMemberDefinition? implicitContentChild, XamlObjectDefinition objectDefinition)
+		{
+			if (implicitContentChild != null)
+			{
+				var elementType = FindType(objectDefinition.Type);
+
+				if (elementType != null)
+				{
+					var contentProperty = FindContentProperty(elementType);
+
+					if (contentProperty != null && IsLazyVisualStateManagerProperty(contentProperty))
+					{
+						return contentProperty;
+					}
+				}
+			}
+
+			return null;
+		}
+
 		private bool IsXLoadMember(XamlMemberDefinition member) =>
 			member.Member.Name == "Load"
 			&& member.Member.PreferredXamlNamespace == XamlConstants.XamlXmlNamespace;
@@ -4611,26 +4673,51 @@ private string RewriteAttachedPropertyPath(string value)
 
 		private void BuildLiteralProperties(IIndentedStringBuilder writer, XamlObjectDefinition objectDefinition, string? closureName = null)
 		{
-			TryAnnotateWithGeneratorSource(writer);
-			var closingPunctuation = string.IsNullOrWhiteSpace(closureName) ? "," : ";";
+			var extendedProperties = GetExtendedProperties(objectDefinition);
+
+			bool PropertyFilter(XamlMemberDefinition member)
+				=> IsType(objectDefinition.Type, member.Member.DeclaringType)
+						&& !IsAttachedProperty(member)
+						&& !IsLazyVisualStateManagerProperty(member)
+						&& FindEventType(member.Member) == null
+						&& member.Member.Name != "_UnknownContent"; // We are defining the elements of a collection explicitly declared in XAML
+
+			BuildLiteralPropertiesWithFilter(writer, objectDefinition, closureName, extendedProperties, PropertyFilter);
+		}
 
+		private void BuildLiteralLazyVisualStateManagerProperties(IIndentedStringBuilder writer, XamlObjectDefinition objectDefinition, string? closureName = null)
+		{
 			var extendedProperties = GetExtendedProperties(objectDefinition);
 
-			var objectUid = GetObjectUid(objectDefinition);
+			bool PropertyFilter(XamlMemberDefinition member)
+				=> IsLazyVisualStateManagerProperty(member);
+
+			BuildLiteralPropertiesWithFilter(writer, objectDefinition, closureName, extendedProperties, PropertyFilter);
+		}
 
+		private void BuildLiteralPropertiesWithFilter(
+			IIndentedStringBuilder writer,
+			XamlObjectDefinition objectDefinition,
+			string? closureName,
+			IEnumerable<XamlMemberDefinition> extendedProperties,
+			Func<XamlMemberDefinition, bool> propertyPredicate
+		)
+		{
 			if (extendedProperties.Any())
 			{
+				TryAnnotateWithGeneratorSource(writer);
+
+				var objectUid = GetObjectUid(objectDefinition);
+				var closingPunctuation = string.IsNullOrWhiteSpace(closureName) ? "," : ";";
+
 				foreach (var member in extendedProperties)
 				{
 					var fullValueSetter = string.IsNullOrWhiteSpace(closureName) ? member.Member!.Name : "{0}.{1}".InvariantCultureFormat(closureName, member.Member!.Name);
 
 					// Exclude attached properties, must be set in the extended apply section.
 					// If there is no type attached, this can be a binding.
-					if (IsType(objectDefinition.Type, member.Member.DeclaringType)
-						&& !IsAttachedProperty(member)
-						&& FindEventType(member.Member) == null
-						&& member.Member.Name != "_UnknownContent" // We are defining the elements of a collection explicitly declared in XAML
-					)
+					// Exclude lazy initialized properties, those are always in the extended block.
+					if (propertyPredicate(member))
 					{
 						if (member.Objects.None())
 						{
@@ -4740,6 +4827,27 @@ private void BuildLiteralProperties(IIndentedStringBuilder writer, XamlObjectDef
 			}
 		}
 
+		private bool IsLazyVisualStateManagerProperty(XamlMemberDefinition member)
+			=> _isLazyVisualStateManagerEnabled
+				&& member.Owner != null
+				&& member.Owner.Type.Name switch
+				{
+					"VisualState" => member.Member.Name == "Storyboard"
+									|| member.Member.Name == "Setters",
+					"VisualTransition" => member.Member.Name == "Storyboard",
+					_ => false,
+				};
+
+		private bool IsLazyVisualStateManagerProperty(IPropertySymbol property)
+			=> _isLazyVisualStateManagerEnabled
+				&& property.ContainingSymbol.Name switch
+			{
+				"VisualState" => property.Name == "Storyboard"
+								|| property.Name == "Setters",
+				"VisualTransition" => property.Name == "Storyboard",
+				_ => false,
+			};
+
 		/// <summary>
 		/// Determines if the member is inline initializable and the first item is not a new collection instance
 		/// </summary>
@@ -4831,6 +4939,7 @@ private IEnumerable<XamlMemberDefinition> GetExtendedProperties(XamlObjectDefini
 						m.Member.Name == "Style" && HasBindingMarkupExtension(m)
 					)
 					|| IsAttachedProperty(m)
+					|| IsLazyVisualStateManagerProperty(m)
 					||
 					(
 						// If the object is a collection and it has both _UnknownContent (i.e. an item) and other properties defined,

src/Uno.UI.RuntimeTests/Helpers/ThemeHelper.cs

@@ -17,9 +17,14 @@ public static IDisposable UseDarkTheme()
 		{
 			var root = Window.Current.Content as FrameworkElement;
 			Assert.IsNotNull(root);
-			var currentTheme = root!.RequestedTheme;
+			var currentTheme = Application.Current.RequestedTheme;
 			root.RequestedTheme = ElementTheme.Dark;
-			return new DisposableAction(() => root.RequestedTheme = currentTheme);
+			Console.WriteLine($"applying currentTheme={currentTheme}");
+			return new DisposableAction(() =>
+			{
+				Console.WriteLine($"restoring currentTheme={currentTheme}");
+				root.RequestedTheme = currentTheme == ApplicationTheme.Light ? ElementTheme.Light : ElementTheme.Dark;
+			});
 		}
 	}
 }

src/Uno.UI.Tests/Uno.UI.Tests.csproj

@@ -99,6 +99,7 @@
 		<Page Include="Windows_UI_Xaml\**\*.xaml" />
 		<Page Include="Windows_UI_Xaml_Data\**\*.xaml" />
 		<Page Include="Windows_UI_Xaml_Controls\**\*.xaml" />
+		<Page Include="Windows_UI_Xaml_Markup\**\*.xaml" />
 		<Page Include="App\**\*.xaml" />
 		<None Remove="Lottie\animation.json" />
 		<Page Include="..\SamplesApp\UITests.Shared\Windows_UI_Xaml\Resources\Test_Dictionary_Linked.xaml" Link="App/Linked/Test_Dictionary_Linked.xaml" />

src/Uno.UI.Tests/Windows_UI_Xaml_Markup/VisualStateManager_Lazy_Tests/Controls/When_VisualStateManager_Lazy.xaml

@@ -0,0 +1,83 @@
+<UserControl
+    x:Class="Uno.UI.Tests.Windows_UI_Xaml_Markup.VisualStateManager_Lazy_Tests.Controls.When_VisualStateManager_Lazy"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:local="using:Uno.UI.Tests.Windows_UI_Xaml_Markup.VisualStateManager_Lazy_Tests.Controls"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d">
+
+	<Grid>
+		<VisualStateManager.VisualStateGroups>
+			<VisualStateGroup x:Name="CommonStates">
+				<VisualStateGroup.Transitions>
+
+					<VisualTransition From="Normal" To="PointerOver">
+						<Storyboard>
+							<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Background">
+								<DiscreteObjectKeyFrame KeyTime="0" Value="Transparent" />
+							</ObjectAnimationUsingKeyFrames>
+							<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="BorderBrush">
+								<DiscreteObjectKeyFrame KeyTime="0" Value="Transparent" />
+							</ObjectAnimationUsingKeyFrames>
+						</Storyboard>
+					</VisualTransition>
+
+				</VisualStateGroup.Transitions>
+
+				<VisualState x:Name="Normal">
+					<Storyboard>
+						<PointerUpThemeAnimation Storyboard.TargetName="border1" />
+					</Storyboard>
+				</VisualState>
+
+				<VisualState x:Name="PointerOver">
+					<Storyboard>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Background">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBackgroundPointerOver}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="BorderBrush">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBorderBrushPointerOver}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Foreground">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonForegroundPointerOver}" />
+						</ObjectAnimationUsingKeyFrames>
+						<PointerUpThemeAnimation Storyboard.TargetName="border1" />
+					</Storyboard>
+				</VisualState>
+
+				<VisualState x:Name="Pressed">
+					<Storyboard>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Background">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBackgroundPressed}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="BorderBrush">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBorderBrushPressed}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Foreground">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonForegroundPressed}" />
+						</ObjectAnimationUsingKeyFrames>
+						<PointerDownThemeAnimation Storyboard.TargetName="border1" />
+					</Storyboard>
+				</VisualState>
+
+				<VisualState x:Name="Disabled">
+					<Storyboard>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Background">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBackgroundDisabled}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="BorderBrush">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonBorderBrushDisabled}" />
+						</ObjectAnimationUsingKeyFrames>
+						<ObjectAnimationUsingKeyFrames Storyboard.TargetName="border1" Storyboard.TargetProperty="Foreground">
+							<DiscreteObjectKeyFrame KeyTime="0" Value="{ThemeResource ButtonForegroundDisabled}" />
+						</ObjectAnimationUsingKeyFrames>
+					</Storyboard>
+				</VisualState>
+			</VisualStateGroup>
+		</VisualStateManager.VisualStateGroups>
+
+		<ContentPresenter x:Name="border1" x:FieldModifier="public" x:Load="false" />
+
+	</Grid>
+</UserControl>

src/Uno.UI.Tests/Windows_UI_Xaml_Markup/VisualStateManager_Lazy_Tests/Controls/When_VisualStateManager_Lazy.xaml.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices.WindowsRuntime;
+using Windows.Foundation;
+using Windows.Foundation.Collections;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Controls.Primitives;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Media;
+using Windows.UI.Xaml.Navigation;
+
+// The User Control item template is documented at https://go.microsoft.com/fwlink/?LinkId=234236
+
+namespace Uno.UI.Tests.Windows_UI_Xaml_Markup.VisualStateManager_Lazy_Tests.Controls
+{
+	public sealed partial class When_VisualStateManager_Lazy : UserControl
+	{
+		public When_VisualStateManager_Lazy()
+		{
+			this.InitializeComponent();
+		}
+	}
+}