[Android] Fix App Unresponsive when prompting the user from a new page

src/Controls/src/Core/Platform/AlertManager/AlertManager.Android.cs

@@ -109,6 +109,12 @@ void OnPageBusy(IView sender, bool enabled)
 
 			void OnActionSheetRequested(IView sender, ActionSheetArguments arguments)
 			{
+				// Wait for handler to be ready before showing dialog
+				if (WaitForHandlerIfNeeded(sender, () => OnActionSheetRequested(sender, arguments)))
+				{
+					return;
+				}
+
 				// Verify that the page making the request is part of this activity 
 				if (!PageIsInThisContext(sender))
 				{
@@ -168,6 +174,12 @@ void OnActionSheetRequested(IView sender, ActionSheetArguments arguments)
 
 			void OnAlertRequested(IView sender, AlertArguments arguments)
 			{
+				// Wait for handler to be ready before showing dialog
+				if (WaitForHandlerIfNeeded(sender, () => OnAlertRequested(sender, arguments)))
+				{
+					return;
+				}
+
 				// Verify that the page making the request is part of this activity 
 				if (!PageIsInThisContext(sender))
 				{
@@ -248,6 +260,12 @@ TextDirection GetTextDirection(IView sender, FlowDirection flowDirection)
 
 			void OnPromptRequested(IView sender, PromptArguments arguments)
 			{
+				// Wait for handler to be ready before showing dialog
+				if (WaitForHandlerIfNeeded(sender, () => OnPromptRequested(sender, arguments)))
+				{
+					return;
+				}
+
 				// Verify that the page making the request is part of this activity 
 				if (!PageIsInThisContext(sender))
 				{
@@ -290,6 +308,22 @@ void OnPromptRequested(IView sender, PromptArguments arguments)
 				editText.RequestFocus();
 			}
 
+			bool WaitForHandlerIfNeeded(IView sender, System.Action action)
+			{
+				if (sender.Handler is null && sender is VisualElement ve)
+				{
+					void OnHandlerReady(object s, EventArgs e)
+					{
+						ve.HandlerChanged -= OnHandlerReady;
+						action();
+					}
+
+					ve.HandlerChanged += OnHandlerReady;
+					return true;
+				}
+				return false;
+			}
+
 			void UpdateProgressBarVisibility(bool isBusy)
 			{
 				int progressLayoutId = 16908999;

src/Controls/tests/TestCases.HostApp/Issues/Issue25585.cs

@@ -0,0 +1,52 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 25585, "App Unresponsive when prompting the user from a new page", PlatformAffected.Android)]
+
+public class Issue25585 : Shell
+{
+	public Issue25585()
+	{
+		this.FlyoutBehavior = FlyoutBehavior.Flyout;
+
+		var shellContent = new ShellContent
+		{
+			Title = "Second Page",
+			Route = "MainPage",
+			Content = new Issue25585ContentPage()
+		};
+
+		Items.Add(new ShellContent
+		{
+			Title = "First Page",
+			Route = "First",
+			Content = new ContentPage
+			{
+				Content = new Label
+				{
+					HorizontalOptions = LayoutOptions.Center,
+					VerticalOptions = LayoutOptions.Center,
+					Text = "Go to SecondPage",
+					AutomationId = "GoToSecondPage",
+				}
+			}
+		});
+		Items.Add(shellContent);
+	}
+}
+
+public class Issue25585ContentPage : ContentPage
+{
+	public Issue25585ContentPage()
+	{
+		Content = new StackLayout
+		{
+			Children =
+				{
+					new Label { Text = "If DisplayAlert is shown, the test passed" },
+				}
+		};
+		DisplayAlert("Hi", "This is from Constructor", "OK", "Cancel");
+	}
+}
+
+

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue25585.cs

@@ -0,0 +1,25 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue25585 : _IssuesUITest
+{
+	public Issue25585(TestDevice device) : base(device) { }
+
+	public override string Issue => "App Unresponsive when prompting the user from a new page";
+	[Test]
+	[Category(UITestCategories.DisplayAlert)]
+	public void VerifyDisplayAlertIsShown()
+	{
+		App.WaitForElement("GoToSecondPage");
+		App.TapShellFlyoutIcon();
+		App.Tap("Second Page");
+#if MACCATALYST
+		App.WaitForElement(AppiumQuery.ById($"action-button--{999 - 0}"));
+#else
+		App.WaitForElement("OK");
+#endif
+	}
+}