feat: Add support for EventTrigger

src/SamplesApp/UITests.Shared/Windows_UI_Xaml/EventTrigger_Loaded.xaml

@@ -0,0 +1,36 @@
+<Page x:Class="UITests.Shared.Windows_UI_Xaml.EventTrigger_Loaded"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+
+	<Page.Resources>
+		<Storyboard x:Name="FadeInStoryboard">
+			<DoubleAnimation Storyboard.TargetName="TargetBorder"
+			                 Storyboard.TargetProperty="Opacity"
+			                 From="0"
+			                 To="1"
+			                 Duration="0:0:1" />
+		</Storyboard>
+	</Page.Resources>
+
+	<Grid>
+		<Border x:Name="TargetBorder"
+		        Width="200"
+		        Height="200"
+		        Background="{ThemeResource SystemAccentColorBrush}"
+		        HorizontalAlignment="Center"
+		        VerticalAlignment="Center"
+		        Opacity="0">
+			<TextBlock Text="Fading In..."
+			           HorizontalAlignment="Center"
+			           VerticalAlignment="Center"
+			           Foreground="{ThemeResource SystemControlForegroundBaseHighBrush}" />
+
+			<Border.Triggers>
+				<EventTrigger>
+					<BeginStoryboard Storyboard="{StaticResource FadeInStoryboard}" />
+				</EventTrigger>
+			</Border.Triggers>
+		</Border>
+	</Grid>
+</Page>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml/EventTrigger_Loaded.xaml.cs

@@ -0,0 +1,12 @@
+using Microsoft.UI.Xaml.Controls;
+
+namespace UITests.Shared.Windows_UI_Xaml
+{
+	public sealed partial class EventTrigger_Loaded : Page
+	{
+		public EventTrigger_Loaded()
+		{
+			this.InitializeComponent();
+		}
+	}
+}

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml/Given_EventTrigger.cs

@@ -0,0 +1,176 @@
+using System.Threading.Tasks;
+using Private.Infrastructure;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Media.Animation;
+
+namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml;
+
+[TestClass]
+[RunsOnUIThread]
+public class Given_EventTrigger
+{
+	[TestMethod]
+	public async Task When_EventTrigger_With_BeginStoryboard_On_Loaded()
+	{
+		var grid = new Grid
+		{
+			Width = 100,
+			Height = 100
+		};
+
+		var border = new Border
+		{
+			Width = 50,
+			Height = 50,
+			Opacity = 0
+		};
+
+		// Create storyboard to animate opacity
+		var storyboard = new Storyboard();
+		var animation = new DoubleAnimation
+		{
+			From = 0,
+			To = 1,
+			Duration = new Duration(TimeSpan.FromMilliseconds(100))
+		};
+		Storyboard.SetTarget(animation, border);
+		Storyboard.SetTargetProperty(animation, "Opacity");
+		storyboard.Children.Add(animation);
+
+		// Create BeginStoryboard action
+		var beginStoryboard = new BeginStoryboard
+		{
+			Storyboard = storyboard
+		};
+
+		// Create EventTrigger
+		var eventTrigger = new EventTrigger();
+		eventTrigger.Actions.Add(beginStoryboard);
+
+		// Add trigger to border
+		border.Triggers.Add(eventTrigger);
+
+		grid.Children.Add(border);
+
+		// Add to visual tree
+		TestServices.WindowHelper.WindowContent = grid;
+		await TestServices.WindowHelper.WaitForLoaded(grid);
+		await TestServices.WindowHelper.WaitForIdle();
+
+		// Give the animation time to start and complete
+		await Task.Delay(200);
+
+		// Verify that the storyboard ran and opacity changed
+		Assert.AreEqual(1.0, border.Opacity, 0.01, "Border opacity should be 1 after storyboard completes");
+	}
+
+	[TestMethod]
+	public async Task When_EventTrigger_Without_RoutedEvent_Defaults_To_Loaded()
+	{
+		bool storyboardStarted = false;
+
+		var border = new Border
+		{
+			Width = 50,
+			Height = 50
+		};
+
+		// Create storyboard
+		var storyboard = new Storyboard();
+		storyboard.Completed += (s, e) => storyboardStarted = true;
+
+		// Create BeginStoryboard action
+		var beginStoryboard = new BeginStoryboard
+		{
+			Storyboard = storyboard
+		};
+
+		// Create EventTrigger without setting RoutedEvent
+		var eventTrigger = new EventTrigger();
+		eventTrigger.Actions.Add(beginStoryboard);
+
+		// Add trigger to border
+		border.Triggers.Add(eventTrigger);
+
+		// Add to visual tree
+		TestServices.WindowHelper.WindowContent = border;
+		await TestServices.WindowHelper.WaitForLoaded(border);
+		await TestServices.WindowHelper.WaitForIdle();
+
+		// Wait for storyboard to complete
+		await TestServices.WindowHelper.WaitFor(() => storyboardStarted);
+
+		Assert.IsTrue(storyboardStarted, "Storyboard should have started when element loaded");
+	}
+
+	[TestMethod]
+	public async Task When_Multiple_Actions_In_EventTrigger()
+	{
+		int action1Executed = 0;
+		int action2Executed = 0;
+
+		var border = new Border
+		{
+			Width = 50,
+			Height = 50
+		};
+
+		// Create first storyboard
+		var storyboard1 = new Storyboard();
+		storyboard1.Completed += (s, e) => action1Executed++;
+
+		// Create second storyboard
+		var storyboard2 = new Storyboard();
+		storyboard2.Completed += (s, e) => action2Executed++;
+
+		// Create BeginStoryboard actions
+		var beginStoryboard1 = new BeginStoryboard { Storyboard = storyboard1 };
+		var beginStoryboard2 = new BeginStoryboard { Storyboard = storyboard2 };
+
+		// Create EventTrigger with multiple actions
+		var eventTrigger = new EventTrigger();
+		eventTrigger.Actions.Add(beginStoryboard1);
+		eventTrigger.Actions.Add(beginStoryboard2);
+
+		// Add trigger to border
+		border.Triggers.Add(eventTrigger);
+
+		// Add to visual tree
+		TestServices.WindowHelper.WindowContent = border;
+		await TestServices.WindowHelper.WaitForLoaded(border);
+		await TestServices.WindowHelper.WaitForIdle();
+
+		// Wait for storyboards to complete
+		await TestServices.WindowHelper.WaitFor(() => action1Executed > 0 && action2Executed > 0);
+
+		Assert.AreEqual(1, action1Executed, "First storyboard should have executed");
+		Assert.AreEqual(1, action2Executed, "Second storyboard should have executed");
+	}
+
+	[TestMethod]
+	public void When_EventTrigger_With_Non_Loaded_Event_Throws()
+	{
+		var eventTrigger = new EventTrigger();
+
+		// Create a custom routed event (not Loaded)
+		var customEvent = new RoutedEvent(Uno.UI.Xaml.RoutedEventFlag.None, "CustomEvent");
+
+		// Attempting to set a non-Loaded RoutedEvent should throw
+		Assert.ThrowsException<NotSupportedException>(() =>
+		{
+			eventTrigger.RoutedEvent = customEvent;
+		}, "Setting a non-Loaded RoutedEvent should throw NotSupportedException");
+	}
+
+	[TestMethod]
+	public void When_EventTrigger_With_Loaded_Event_Succeeds()
+	{
+		var eventTrigger = new EventTrigger();
+
+		// Setting the Loaded event should succeed
+		eventTrigger.RoutedEvent = FrameworkElement.LoadedEvent;
+
+		Assert.AreEqual(FrameworkElement.LoadedEvent, eventTrigger.RoutedEvent);
+	}
+}

src/Uno.UI/Generated/3.0.0.0/Microsoft.UI.Xaml.Media.Animation/BeginStoryboard.cs

@@ -4,40 +4,14 @@
 namespace Microsoft.UI.Xaml.Media.Animation
 {
 	[global::Microsoft.UI.Xaml.Markup.ContentPropertyAttribute(Name = "Storyboard")]
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
+#if false || false || false || false || false || false || false
 	[global::Uno.NotImplemented]
 #endif
 	public partial class BeginStoryboard : global::Microsoft.UI.Xaml.TriggerAction
 	{
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public global::Microsoft.UI.Xaml.Media.Animation.Storyboard Storyboard
-		{
-			get
-			{
-				return (global::Microsoft.UI.Xaml.Media.Animation.Storyboard)this.GetValue(StoryboardProperty);
-			}
-			set
-			{
-				this.SetValue(StoryboardProperty, value);
-			}
-		}
-#endif
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public static global::Microsoft.UI.Xaml.DependencyProperty StoryboardProperty { get; } =
-		Microsoft.UI.Xaml.DependencyProperty.Register(
-			nameof(Storyboard), typeof(global::Microsoft.UI.Xaml.Media.Animation.Storyboard),
-			typeof(global::Microsoft.UI.Xaml.Media.Animation.BeginStoryboard),
-			new Microsoft.UI.Xaml.FrameworkPropertyMetadata(default(global::Microsoft.UI.Xaml.Media.Animation.Storyboard)));
-#endif
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public BeginStoryboard()
-		{
-			global::Windows.Foundation.Metadata.ApiInformation.TryRaiseNotImplemented("Microsoft.UI.Xaml.Media.Animation.BeginStoryboard", "BeginStoryboard.BeginStoryboard()");
-		}
-#endif
+		// Skipping already declared property Storyboard
+		// Skipping already declared property StoryboardProperty
+		// Skipping already declared method Microsoft.UI.Xaml.Media.Animation.BeginStoryboard.BeginStoryboard()
 		// Forced skipping of method Microsoft.UI.Xaml.Media.Animation.BeginStoryboard.BeginStoryboard()
 		// Forced skipping of method Microsoft.UI.Xaml.Media.Animation.BeginStoryboard.Storyboard.get
 		// Forced skipping of method Microsoft.UI.Xaml.Media.Animation.BeginStoryboard.Storyboard.set

src/Uno.UI/Generated/3.0.0.0/Microsoft.UI.Xaml/EventTrigger.cs

@@ -4,42 +4,14 @@
 namespace Microsoft.UI.Xaml
 {
 	[global::Microsoft.UI.Xaml.Markup.ContentPropertyAttribute(Name = "Actions")]
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
+#if false || false || false || false || false || false || false
 	[global::Uno.NotImplemented]
 #endif
 	public partial class EventTrigger : global::Microsoft.UI.Xaml.TriggerBase
 	{
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public global::Microsoft.UI.Xaml.RoutedEvent RoutedEvent
-		{
-			get
-			{
-				throw new global::System.NotImplementedException("The member RoutedEvent EventTrigger.RoutedEvent is not implemented. For more information, visit https://aka.platform.uno/notimplemented#m=RoutedEvent%20EventTrigger.RoutedEvent");
-			}
-			set
-			{
-				global::Windows.Foundation.Metadata.ApiInformation.TryRaiseNotImplemented("Microsoft.UI.Xaml.EventTrigger", "RoutedEvent EventTrigger.RoutedEvent");
-			}
-		}
-#endif
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public global::Microsoft.UI.Xaml.TriggerActionCollection Actions
-		{
-			get
-			{
-				throw new global::System.NotImplementedException("The member TriggerActionCollection EventTrigger.Actions is not implemented. For more information, visit https://aka.platform.uno/notimplemented#m=TriggerActionCollection%20EventTrigger.Actions");
-			}
-		}
-#endif
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public EventTrigger()
-		{
-			global::Windows.Foundation.Metadata.ApiInformation.TryRaiseNotImplemented("Microsoft.UI.Xaml.EventTrigger", "EventTrigger.EventTrigger()");
-		}
-#endif
+		// Skipping already declared property RoutedEvent
+		// Skipping already declared property Actions
+		// Skipping already declared method Microsoft.UI.Xaml.EventTrigger.EventTrigger()
 		// Forced skipping of method Microsoft.UI.Xaml.EventTrigger.EventTrigger()
 		// Forced skipping of method Microsoft.UI.Xaml.EventTrigger.RoutedEvent.get
 		// Forced skipping of method Microsoft.UI.Xaml.EventTrigger.RoutedEvent.set

src/Uno.UI/Generated/3.0.0.0/Microsoft.UI.Xaml/FrameworkElement.cs

@@ -63,16 +63,7 @@ public string Language
 		// Skipping already declared property BaseUri
 		// Skipping already declared property IsLoaded
 		// Skipping already declared property Parent
-#if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
-		public global::Microsoft.UI.Xaml.TriggerCollection Triggers
-		{
-			get
-			{
-				throw new global::System.NotImplementedException("The member TriggerCollection FrameworkElement.Triggers is not implemented. For more information, visit https://aka.platform.uno/notimplemented#m=TriggerCollection%20FrameworkElement.Triggers");
-			}
-		}
-#endif
+		// Skipping already declared property Triggers
 #if __ANDROID__ || __IOS__ || __TVOS__ || IS_UNIT_TESTS || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "__TVOS__", "IS_UNIT_TESTS", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__")]
 		public static global::Microsoft.UI.Xaml.DependencyProperty ActualHeightProperty { get; } =