[Windows]Fix for AdaptiveTrigger Not Firing When Changing Window Width Programmatically

src/Controls/src/Core/Window/Window.cs

@@ -44,11 +44,13 @@ public partial class Window : NavigableElement, IWindow, IToolbarElement, IMenuB
 
 		/// <summary>Bindable property for <see cref="Width"/>.</summary>
 		public static readonly BindableProperty WidthProperty = BindableProperty.Create(
-			nameof(Width), typeof(double), typeof(Window), Primitives.Dimension.Unset);
+			nameof(Width), typeof(double), typeof(Window), Primitives.Dimension.Unset,
+			propertyChanged: OnSizePropertyChanged);
 
 		/// <summary>Bindable property for <see cref="Height"/>.</summary>
 		public static readonly BindableProperty HeightProperty = BindableProperty.Create(
-			nameof(Height), typeof(double), typeof(Window), Primitives.Dimension.Unset);
+			nameof(Height), typeof(double), typeof(Window), Primitives.Dimension.Unset,
+			propertyChanged: OnSizePropertyChanged);        
 
 		/// <summary>Bindable property for <see cref="MaximumWidth"/>.</summary>
 		public static readonly BindableProperty MaximumWidthProperty = BindableProperty.Create(
@@ -228,6 +230,16 @@ double GetSizeCoordinate(BindableProperty property)
 
 		int _batchFrameUpdate = 0;
 
+		static void OnSizePropertyChanged(BindableObject bindable, object oldValue, object newValue)
+		{
+			var window = (Window)bindable;
+			// Only trigger SizeChanged if not being updated from platform (FrameChanged)
+			if (window._batchFrameUpdate == 0)
+			{
+				window.SizeChanged?.Invoke(window, EventArgs.Empty);
+			}
+		}
+
 		void IWindow.FrameChanged(Rect frame)
 		{
 			if (new Rect(X, Y, Width, Height) == frame)

src/Controls/tests/TestCases.HostApp/Issues/Issue27646.cs

@@ -0,0 +1,99 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 27646, "AdaptiveTrigger not firing when changing window width programmatically only", PlatformAffected.UWP)]
+public class Issue27646 : ContentPage
+{
+	Label indicatorLabel;
+	Label statusLabel;
+
+	public Issue27646()
+	{
+		var stackLayout = new VerticalStackLayout
+		{
+			Padding = 20,
+			Spacing = 10
+		};
+
+		var instructionLabel = new Label
+		{
+			Text = "Click button to resize window. Label text should change at 600px window width.",
+			AutomationId = "InstructionLabel"
+		};
+		stackLayout.Add(instructionLabel);
+
+		statusLabel = new Label
+		{
+			Text = "Window width: Unknown",
+			AutomationId = "StatusLabel",
+			FontAttributes = FontAttributes.Bold
+		};
+		stackLayout.Add(statusLabel);
+
+		var resizeButton = new Button
+		{
+			Text = "Resize Window",
+			AutomationId = "ResizeButton"
+		};
+		resizeButton.Clicked += OnResizeClicked;
+		stackLayout.Add(resizeButton);
+
+		indicatorLabel = new Label
+		{
+			Text = "Initial",
+			WidthRequest = 200,
+			HeightRequest = 100,
+			HorizontalTextAlignment = TextAlignment.Center,
+			VerticalTextAlignment = TextAlignment.Center,
+			AutomationId = "IndicatorLabel"
+		};
+		stackLayout.Add(indicatorLabel);
+
+		Content = stackLayout;
+
+		VisualStateManager.SetVisualStateGroups(indicatorLabel, new VisualStateGroupList
+		{
+			new VisualStateGroup
+			{
+				Name = "WindowWidthStates",
+				States =
+				{
+					new VisualState
+					{
+						Name = "Narrow",
+						StateTriggers =
+						{
+							new AdaptiveTrigger { MinWindowWidth = 0 }
+						},
+						Setters =
+						{
+							new Setter { Property = Label.TextProperty, Value = "Narrow Window" }
+						}
+					},
+					new VisualState
+					{
+						Name = "Wide",
+						StateTriggers =
+						{
+							new AdaptiveTrigger { MinWindowWidth = 600 }
+						},
+						Setters =
+						{
+							new Setter { Property = Label.TextProperty, Value = "Wide Window" }
+						}
+					}
+				}
+			}
+		});
+	}
+
+	void OnResizeClicked(object sender, EventArgs e)
+	{
+		if (Window is not null)
+		{
+			double newWidth = Window.Width >= 600 ? 550 : 650;
+			Window.Width = newWidth;
+
+			statusLabel.Text = $"Window width: {newWidth}px";
+		}
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue27646.cs

@@ -0,0 +1,33 @@
+#if WINDOWS // MacCatalyst don't support programmatic window resizing. So, ignored test on MacCatalyst.
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue27646 : _IssuesUITest
+{
+	public override string Issue => "AdaptiveTrigger not firing when changing window width programmatically only";
+
+	public Issue27646(TestDevice device) : base(device) { }
+
+	[Test]
+	[Category(UITestCategories.Window)]
+	public void AdaptiveTriggerShouldFireWhenWindowWidthChangedProgrammatically()
+	{
+		App.WaitForElement("ResizeButton");
+
+		App.Tap("ResizeButton");
+
+		var indicatorAfterFirstClick = App.FindElement("IndicatorLabel");
+		Assert.That(indicatorAfterFirstClick.GetText(), Is.EqualTo("Narrow Window"),
+			"Label should show 'Narrow Window' after resizing to 550px");
+
+		App.Tap("ResizeButton");
+
+		var indicatorAfterSecondClick = App.FindElement("IndicatorLabel");
+		Assert.That(indicatorAfterSecondClick.GetText(), Is.EqualTo("Wide Window"),
+			"Label should show 'Wide Window' after resizing to 650px");
+	}
+}
+#endif