Fix for Page OnAppearing triggered twice when navigating via ShellItem change with PresentationMode set to Modal

src/Controls/src/Core/Shell/ShellSection.cs

@@ -992,12 +992,22 @@ protected virtual void OnRemovePage(Page page)
 		}
 
 		internal bool IsVisibleSection => Parent?.Parent is Shell shell && shell.CurrentItem?.CurrentItem == this;
+
 		void PresentedPageDisappearing()
 		{
 			if (this is IShellSectionController sectionController)
 			{
 				CurrentItem?.SendDisappearing();
-				sectionController.PresentedPage?.SendDisappearing();
+				var presentedPage = sectionController.PresentedPage;
+				if (presentedPage is not null)
+				{
+					// Don't send disappearing to a modal page if we're switching ShellItems
+					// The modal belongs to the new ShellItem, not the old one being disappeared
+					if (IsVisibleSection)
+					{
+						presentedPage.SendDisappearing();
+					}
+				}
 			}
 		}
 

src/Controls/tests/Core.UnitTests/ShellModalAppearingTests.cs

@@ -0,0 +1,164 @@
+using System.Threading.Tasks;
+using Microsoft.Maui.Controls.Internals;
+using Xunit;
+
+namespace Microsoft.Maui.Controls.Core.UnitTests
+{
+	public class ShellModalAppearingTests : ShellTestBase
+	{
+		[Fact]
+		public async Task ModalPageOnAppearingTriggeredOnceWithShellItemChangeToModal()
+		{
+			// Test the exact scenario from the issue: navigating from one ShellItem to another with a modal page
+			TestShell shell = new TestShell();
+
+			Routing.RegisterRoute("ModalPage", typeof(ModalPage31584));
+
+			var mainItem = CreateShellItem(shellItemRoute: "MainPage", shellSectionRoute: "MainSection", shellContentRoute: "MainContent");
+			var homeItem = CreateShellItem(shellItemRoute: "Home", shellSectionRoute: "HomeSection", shellContentRoute: "HomeContent");
+
+			shell.Items.Add(mainItem);
+			shell.Items.Add(homeItem);
+
+			// Start on MainPage
+			Assert.Equal(mainItem, shell.CurrentItem);
+
+			// Navigate to //Home/ModalPage (changes ShellItem AND pushes modal)
+			await shell.GoToAsync("//Home/ModalPage");
+
+			// Verify we switched to Home ShellItem
+			Assert.Equal(homeItem, shell.CurrentItem);
+
+			// Get the modal page from the Home ShellItem's section
+			var homeSection = homeItem.Items[0];
+			var modalPage = (homeSection as IShellSectionController).PresentedPage as ModalPage31584;
+
+			Assert.NotNull(modalPage);
+
+			// The bug would cause OnAppearing to be called twice:
+			// 1. When the modal is pushed to the new ShellItem
+			// 2. When the old ShellItem's section tries to send disappearing to it
+			// The fix ensures OnAppearing is only called once
+			Assert.Equal(1, modalPage.AppearingCount);
+		}
+
+		[Fact]
+		public async Task ModalPageDisappearingNotCalledByOldShellItemDuringSwitch()
+		{
+			// This test verifies the core fix: when switching ShellItems with a modal page,
+			// the old ShellItem's section should NOT call SendDisappearing on the modal page
+			// because the modal belongs to the new ShellItem, not the old one
+			TestShell shell = new TestShell();
+
+			Routing.RegisterRoute("ModalPage", typeof(ModalPage31584));
+
+			var mainItem = CreateShellItem(shellItemRoute: "MainPage", shellSectionRoute: "MainSection", shellContentRoute: "MainContent");
+			var homeItem = CreateShellItem(shellItemRoute: "Home", shellSectionRoute: "HomeSection", shellContentRoute: "HomeContent");
+
+			shell.Items.Add(mainItem);
+			shell.Items.Add(homeItem);
+
+			// Navigate to //Home/ModalPage
+			await shell.GoToAsync("//Home/ModalPage");
+
+			var homeSection = homeItem.Items[0];
+			var modalPage = (homeSection as IShellSectionController).PresentedPage as ModalPage31584;
+
+			Assert.NotNull(modalPage);
+
+			// The modal should have appeared once
+			Assert.Equal(1, modalPage.AppearingCount);
+
+			// And should not have disappeared (because it's still visible)
+			Assert.Equal(0, modalPage.DisappearingCount);
+		}
+
+		[Fact]
+		public async Task ModalPageLifecycleCorrectWithNormalModalPush()
+		{
+			// Verify that normal modal push/pop still works correctly after the fix
+			TestShell shell = new TestShell();
+
+			Routing.RegisterRoute("ModalPage", typeof(ModalPage31584));
+
+			shell.Items.Add(CreateShellItem(shellItemRoute: "MainPage", shellSectionRoute: "MainSection", shellContentRoute: "MainContent"));
+
+			// Normal modal navigation (no ShellItem change)
+			await shell.GoToAsync("ModalPage");
+
+			var mainSection = shell.Items[0].Items[0];
+			var modalPage = (mainSection as IShellSectionController).PresentedPage as ModalPage31584;
+
+			Assert.NotNull(modalPage);
+			Assert.Equal(1, modalPage.AppearingCount);
+			Assert.Equal(0, modalPage.DisappearingCount);
+
+			// Pop the modal
+			await shell.GoToAsync("..");
+
+			// Modal should have disappeared once
+			Assert.Equal(1, modalPage.AppearingCount);
+			Assert.Equal(1, modalPage.DisappearingCount);
+		}
+
+		[Fact]
+		public async Task RapidShellItemSwitchingWithModal()
+		{
+			// Test rapidly switching between ShellItems with modals to ensure lifecycle stays correct
+			TestShell shell = new TestShell();
+
+			Routing.RegisterRoute("ModalPage1", typeof(ModalPage31584));
+			Routing.RegisterRoute("ModalPage2", typeof(ModalPage31584));
+
+			shell.Items.Add(CreateShellItem(shellItemRoute: "Item1", shellSectionRoute: "Section1", shellContentRoute: "Content1"));
+			shell.Items.Add(CreateShellItem(shellItemRoute: "Item2", shellSectionRoute: "Section2", shellContentRoute: "Content2"));
+			shell.Items.Add(CreateShellItem(shellItemRoute: "Item3", shellSectionRoute: "Section3", shellContentRoute: "Content3"));
+
+			// Navigate to modal on Item2
+			await shell.GoToAsync("//Item2/ModalPage1");
+			var section2 = shell.Items[1].Items[0];
+			var modal1 = (section2 as IShellSectionController).PresentedPage as ModalPage31584;
+
+			Assert.NotNull(modal1);
+			Assert.Equal(1, modal1.AppearingCount);
+
+			// Switch to Item3 with another modal
+			await shell.GoToAsync("//Item3/ModalPage2");
+			var section3 = shell.Items[2].Items[0];
+			var modal2 = (section3 as IShellSectionController).PresentedPage as ModalPage31584;
+
+			Assert.NotNull(modal2);
+			// Second modal should have appeared exactly once (the bug would cause it to appear twice)
+			Assert.Equal(1, modal2.AppearingCount);
+			Assert.Equal(0, modal2.DisappearingCount);
+		}
+
+		public class ModalPage31584 : ContentPage
+		{
+			public int AppearingCount { get; private set; }
+			public int DisappearingCount { get; private set; }
+
+			public ModalPage31584()
+			{
+				Shell.SetPresentationMode(this, PresentationMode.Modal);
+			}
+
+			protected override void OnAppearing()
+			{
+				base.OnAppearing();
+				AppearingCount++;
+			}
+
+			protected override void OnDisappearing()
+			{
+				base.OnDisappearing();
+				DisappearingCount++;
+			}
+		}
+
+		public ShellModalAppearingTests()
+		{
+			// Routes are already registered in the test methods as needed
+		}
+	}
+}