Fix TabbedPage title displaying incorrectly (#17039)

* Fix TabbedPage title displaying incorrectly

Presently, when a navigation page is created and a tabbed page is added to it with children, the navigation page uses the tabbed page's selected child title as its title. This behavior is unexpected when using standard tabs (tabs on the top) in a navigation page on Android.

Without a custom tabbed page, this behavior makes sense, especially for bottom tabs; however, when a custom tabbed page is defined, it seems that the title should not be overridden.

Fixes #8577

* Add device tests

* Add unit tests

* Updated test

* More tests

* Fixed test not being able to fail

* Changed GetTitle to work with more than just TabbedPages

* Removed tests that deal with Child page titles replacing the Toolbar title

---------

Co-authored-by: Javier Suárez <[email protected]>
Co-authored-by: Dustin Wojciechowski <[email protected]>
Co-authored-by: Dustin Wojciechowski <[email protected]>

src/Controls/src/Core/NavigationPage/NavigationPageToolbar.cs

@@ -158,9 +158,9 @@ void UpdateBackButton()
 
 			// Once we have better logic inside core to handle backbutton visiblity this
 			// code should all go away.
-			// Windows currently doesn't have logic in core to handle back button visibility		
+			// Windows currently doesn't have logic in core to handle back button visibility
 			// Android just handles it as part of core which means you get cool animations
-			// that we don't want to interrupt here.	
+			// that we don't want to interrupt here.
 			// Once it's all built into core we can remove this code and simplify visibility logic
 			if (_currentPage.IsSet(NavigationPage.HasBackButtonProperty))
 			{
@@ -273,7 +273,16 @@ void OnPropertyChanged(object sender, System.ComponentModel.PropertyChangedEvent
 
 		Color GetBarTextColor() => _currentNavigationPage?.BarTextColor;
 		Color GetIconColor() => (_currentPage != null) ? NavigationPage.GetIconColor(_currentPage) : null;
-		string GetTitle() => GetTitleView() != null ? String.Empty : _currentPage?.Title;
+
+		string GetTitle()
+		{
+			if (GetTitleView() != null)
+			{
+				return string.Empty;
+			}
+
+			return _currentNavigationPage?.CurrentPage?.Title;
+		}
 
 		VisualElement GetTitleView()
 		{

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

@@ -56,6 +56,22 @@ public async Task TitleAndTitleViewAreMutuallyExclusive()
 			Assert.Equal("Test Title", toolbar.Title);
 		}
 
+		[Fact]
+		public void ToolbarTitle_UsesTabbedPageTitleWhenSet()
+		{
+			var window = new TestWindow();
+			IToolbarElement toolbarElement = window;
+			var tabbedPage = new TabbedPage
+			{
+				Title = "Test Title",
+				Children = { new ContentPage { Title = "Child Test Title" } },
+			};
+			window.Page = new NavigationPage(tabbedPage);
+
+			var toolbar = (Toolbar)toolbarElement.Toolbar;
+			Assert.Equal(tabbedPage.Title, toolbar.Title);
+		}
+
 		[Fact]
 		public async Task InsertPageBeforeRootPageShowsBackButton()
 		{

src/Controls/tests/DeviceTests/Elements/Toolbar/ToolbarTests.cs

@@ -19,6 +19,7 @@
 #if IOS || MACCATALYST
 using FlyoutViewHandler = Microsoft.Maui.Controls.Handlers.Compatibility.PhoneFlyoutPageRenderer;
 using NavigationViewHandler = Microsoft.Maui.Controls.Handlers.Compatibility.NavigationRenderer;
+using TabbedRenderer = Microsoft.Maui.Controls.Handlers.Compatibility.TabbedRenderer;
 #endif
 
 namespace Microsoft.Maui.DeviceTests
@@ -38,7 +39,11 @@ void SetupBuilder()
 					handlers.AddHandler(typeof(Controls.NavigationPage), typeof(NavigationViewHandler));
 					handlers.AddHandler<Page, PageHandler>();
 					handlers.AddHandler<Controls.Window, WindowHandlerStub>();
-					handlers.AddHandler(typeof(TabbedPage), typeof(TabbedViewHandler));
+					#if IOS || MACCATALYST
+                    handlers.AddHandler(typeof(TabbedPage), typeof(TabbedRenderer));
+#else
+                    handlers.AddHandler(typeof(TabbedPage), typeof(TabbedViewHandler));
+#endif
 
 					SetupShellHandlers(handlers);
 				});