[Windows] - Fix Grid layout not updating when Row/Column changed dynamically

src/Controls/src/Core/Layout/Grid.cs

@@ -406,6 +406,16 @@ static void Invalidate(BindableObject bindable, object oldValue, object newValue
 			if (bindable is Grid grid)
 			{
 				grid.InvalidateMeasure();
+#if WINDOWS
+				// Windows requires explicit parent invalidation for Grid.Row/Column/RowSpan/ColumnSpan changes.
+				// Unlike iOS/Android, Windows doesn't auto-propagate layout invalidation up the hierarchy,
+				// causing dynamic attached property changes to not arrange its children correctly.
+				if (grid.Parent is Grid containerGrid)
+				{
+					containerGrid.InvalidateMeasure();
+					return;
+				}
+#endif
 			}
 			else if (bindable is Element element && element.Parent is Grid parentGrid)
 			{

src/Controls/tests/TestCases.HostApp/Issues/Issue20404.cs

@@ -0,0 +1,138 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 20404, "Dynamic Grid Row/Column changes don't trigger layout update on Windows until window resize", PlatformAffected.UWP)]
+public class Issue20404 : TestContentPage
+{
+	Grid dynamicGrid;
+	Button toggleRowButton;
+	Button toggleColumnButton;
+
+	protected override void Init()
+	{
+		Content = CreateMainGrid();
+	}
+
+	Grid CreateMainGrid()
+	{
+		Grid mainGrid = new Grid
+		{
+			RowSpacing = 8,
+			ColumnSpacing = 8,
+			RowDefinitions =
+			{
+				new RowDefinition { Height = GridLength.Star },
+				new RowDefinition { Height = GridLength.Star },
+				new RowDefinition { Height = GridLength.Auto },
+				new RowDefinition { Height = GridLength.Auto }
+			},
+			ColumnDefinitions =
+			{
+				new ColumnDefinition { Width = GridLength.Star },
+				new ColumnDefinition { Width = GridLength.Star }
+			}
+		};
+
+		AddStaticGrids(mainGrid);
+		AddDynamicGrid(mainGrid);
+		AddControlButtons(mainGrid);
+		return mainGrid;
+	}
+
+	void AddStaticGrids(Grid parent)
+	{
+		Grid topLeft = CreateStaticGrid("Static\n(0,0)", Colors.LightBlue);
+		Grid.SetRow(topLeft, 0);
+		Grid.SetColumn(topLeft, 0);
+		parent.Children.Add(topLeft);
+
+		Grid topRight = CreateStaticGrid("Static\n(0,1)", Colors.LightCoral);
+		Grid.SetRow(topRight, 0);
+		Grid.SetColumn(topRight, 1);
+		parent.Children.Add(topRight);
+
+		Grid bottomLeft = CreateStaticGrid("Static\n(1,0)", Colors.LightGreen);
+		Grid.SetRow(bottomLeft, 1);
+		Grid.SetColumn(bottomLeft, 0);
+		parent.Children.Add(bottomLeft);
+	}
+
+	Grid CreateStaticGrid(string labelText, Color backgroundColor)
+	{
+		Grid grid = new Grid { BackgroundColor = backgroundColor };
+		Label label = new Label
+		{
+			Text = labelText,
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center,
+			TextColor = Colors.Black
+		};
+
+		grid.Children.Add(label);
+		return grid;
+	}
+
+	void AddDynamicGrid(Grid parent)
+	{
+		dynamicGrid = new Grid
+		{
+			BackgroundColor = Colors.DarkBlue,
+			AutomationId = "DynamicGrid"
+		};
+
+		Label label = new Label
+		{
+			Text = "DYNAMIC\nGRID",
+			TextColor = Colors.White,
+			FontAttributes = FontAttributes.Bold,
+			HorizontalOptions = LayoutOptions.Center,
+			VerticalOptions = LayoutOptions.Center,
+			AutomationId = "DynamicLabel"
+		};
+
+		dynamicGrid.Children.Add(label);
+		Grid.SetRow(dynamicGrid, 1);
+		Grid.SetColumn(dynamicGrid, 1);
+
+		parent.Children.Add(dynamicGrid);
+	}
+
+	void AddControlButtons(Grid parent)
+	{
+		toggleRowButton = new Button
+		{
+			Text = "Toggle Row (Current: 1)",
+			AutomationId = "ToggleRowButton"
+		};
+		toggleRowButton.Clicked += OnToggleRowClicked;
+
+		toggleColumnButton = new Button
+		{
+			Text = "Toggle Column (Current: 1)",
+			AutomationId = "ToggleColumnButton"
+		};
+		toggleColumnButton.Clicked += OnToggleColumnClicked;
+
+		StackLayout buttonStack = new StackLayout
+		{
+			Orientation = StackOrientation.Horizontal,
+			HorizontalOptions = LayoutOptions.Center,
+			Children = { toggleRowButton, toggleColumnButton }
+		};
+
+		Grid.SetRow(buttonStack, 3);
+		Grid.SetColumnSpan(buttonStack, 2);
+		parent.Children.Add(buttonStack);
+	}
+
+	void OnToggleRowClicked(object sender, EventArgs e)
+	{
+		Grid.SetRow(dynamicGrid, 0);
+		toggleRowButton.Text = $"Toggle Row (Current: 0)";
+	}
+
+	void OnToggleColumnClicked(object sender, EventArgs e)
+	{
+		Grid.SetColumn(dynamicGrid, 0);
+		toggleColumnButton.Text = $"Toggle Column (Current: 0)";
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue20404.cs

@@ -0,0 +1,24 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue20404 : _IssuesUITest
+{
+	public Issue20404(TestDevice testDevice) : base(testDevice) { }
+
+	public override string Issue => "Dynamic Grid Row/Column changes don't trigger layout update on Windows until window resize";
+
+	[Test]
+	[Category(UITestCategories.Layout)]
+	public void DynamicGridRowColumnChangeShouldInvalidate()
+	{
+		App.WaitForElement("ToggleRowButton");
+		App.Tap("ToggleRowButton");
+		VerifyScreenshot("AfterGridRowToggled");
+		App.WaitForElement("ToggleColumnButton");
+		App.Tap("ToggleColumnButton");
+		VerifyScreenshot("AfterGridColumnToggled");
+	}
+}