[Windows, Catalyst] Fix IsPresented=true Not Working on Initial Value in FlyoutPage

src/Controls/src/Core/Compatibility/Handlers/FlyoutPage/iOS/PhoneFlyoutPageRenderer.cs

@@ -124,6 +124,11 @@ public override void ViewDidAppear(bool animated)
 		{
 			base.ViewDidAppear(animated);
 			Page.SendAppearing();
+			if (!_intialLayoutFinished)
+			{
+				_intialLayoutFinished = true;
+				SetInitialPresented();
+			}
 		}
 
 		public override void ViewDidDisappear(bool animated)
@@ -158,19 +163,6 @@ void SetInitialPresented()
 			UpdateLeftBarButton();
 		}
 
-		public override void ViewWillLayoutSubviews()
-		{
-			// Orientation doesn't seem to be set to a stable correct value until here.
-			// So, we officially process orientation here.
-			if (!_intialLayoutFinished)
-			{
-				_intialLayoutFinished = true;
-				SetInitialPresented();
-			}
-
-			base.ViewWillLayoutSubviews();
-		}
-
 		public override void ViewDidLoad()
 		{
 			base.ViewDidLoad();

src/Controls/src/Core/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+*REMOVED*override Microsoft.Maui.Controls.Handlers.Compatibility.PhoneFlyoutPageRenderer.ViewWillLayoutSubviews() -> void
 ~Microsoft.Maui.Controls.Element.transientNamescope -> Microsoft.Maui.Controls.Internals.INameScope
 Microsoft.Maui.Controls.FlexLayout.CrossPlatformMeasure(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
 override Microsoft.Maui.Controls.ContentPresenter.OnSizeAllocated(double width, double height) -> void

src/Controls/src/Core/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+*REMOVED*override Microsoft.Maui.Controls.Handlers.Compatibility.PhoneFlyoutPageRenderer.ViewWillLayoutSubviews() -> void
 ~Microsoft.Maui.Controls.Element.transientNamescope -> Microsoft.Maui.Controls.Internals.INameScope
 Microsoft.Maui.Controls.FlexLayout.CrossPlatformMeasure(double widthConstraint, double heightConstraint) -> Microsoft.Maui.Graphics.Size
 override Microsoft.Maui.Controls.ContentPresenter.OnSizeAllocated(double width, double height) -> void

src/Controls/tests/TestCases.HostApp/Issues/Issue31372.cs

@@ -0,0 +1,59 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 31372, "IsPresented=true Not Working on Initial Value in FlyoutPage", PlatformAffected.UWP | PlatformAffected.macOS)]
+
+public class Issue31372 : NavigationPage
+{
+	public Issue31372()
+	{
+		PushAsync(new Issue31372Page());
+	}
+}
+
+public class Issue31372Page : FlyoutPage
+{
+	public Issue31372Page()
+	{
+
+		// Create Flyout Page
+		var flyoutPage = new ContentPage
+		{
+			Title = "Flyout",
+			Content = new StackLayout
+			{
+				Children =
+				{
+					new Label
+					{
+						Text = "This is Flyout",
+						AutomationId = "FlyoutLabel"
+					}
+				}
+			}
+		};
+
+		// Create Detail Page
+		var detailPage = new ContentPage
+		{
+			Title = "Detailpage",
+			Content = new StackLayout
+			{
+				Padding = 16,
+				Spacing = 16,
+				Children =
+				{
+					new Label
+					{
+						Text = "This is Detail Page which displays additional information."
+					},
+				}
+			}
+		};
+
+		// Assign Flyout and Detail
+		Flyout = flyoutPage;
+		Detail = new NavigationPage(detailPage);
+		FlyoutLayoutBehavior = FlyoutLayoutBehavior.Popover;
+		IsPresented = true;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31372.cs

@@ -0,0 +1,22 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue31372 : _IssuesUITest
+	{
+		public override string Issue => "IsPresented=true Not Working on Initial Value in FlyoutPage";
+
+		public Issue31372(TestDevice device)
+		: base(device)
+		{ }
+
+		[Test]
+		[Category(UITestCategories.FlyoutPage)]
+		public void VerifyIsPresentedInitialValue()
+		{
+			App.WaitForElement("FlyoutLabel");
+		}
+	}
+}

src/Core/src/Handlers/FlyoutView/FlyoutViewHandler.Windows.cs

@@ -21,12 +21,22 @@ protected override void ConnectHandler(RootNavigationView platformView)
 			_navigationRootManager = MauiContext?.GetNavigationRootManager();
 			platformView.PaneOpened += OnPaneOpened;
 			platformView.PaneClosed += OnPaneClosed;
+			platformView.Loaded += OnLoaded;
+		}
+
+		void OnLoaded(object sender, RoutedEventArgs e)
+		{
+			if (VirtualView is not null)
+			{
+				PlatformView.IsPaneOpen = VirtualView.IsPresented;
+			}
 		}
 
 		protected override void DisconnectHandler(RootNavigationView platformView)
 		{
 			platformView.PaneOpened -= OnPaneOpened;
 			platformView.PaneClosed -= OnPaneClosed;
+			platformView.Loaded -= OnLoaded;
 		}
 
 		void OnPaneOpened(NavigationView sender, object args)