[iOS 26] Fix Shell TitleView not resizing on device rotation

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellPageRendererTracker.cs

@@ -371,6 +371,28 @@ TitleViewContainer CreateTitleViewContainer(View titleView)
 			return new TitleViewContainer(titleView);
 		}
 
+		/// <summary>
+		/// Re-applies the navigation bar frame to the current TitleView container.
+		/// On iOS 26+ the TitleView container uses autoresizing masks with an explicitly set frame
+		/// (see <see cref="CreateTitleViewContainer"/>), so the frame is not automatically recomputed
+		/// when the navigation bar resizes during rotation or window size changes. This explicitly
+		/// resizes the container to match the navigation bar's new dimensions.
+		/// </summary>
+		internal void UpdateTitleViewFrameForOrientation()
+		{
+			if (NavigationItem?.TitleView is not TitleViewContainer titleViewContainer)
+			{
+				return;
+			}
+
+			var navigationBarFrame = ViewController?.NavigationController?.NavigationBar.Frame;
+			if (navigationBarFrame.HasValue)
+			{
+				titleViewContainer.Frame = new CGRect(0, 0, navigationBarFrame.Value.Width, navigationBarFrame.Value.Height);
+				titleViewContainer.LayoutIfNeeded();
+			}
+		}
+
 		void OnTitleViewParentSet(object? sender, EventArgs e)
 		{
 			if (sender is Element element)

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellSectionRenderer.cs

@@ -5,6 +5,7 @@
 using System.Linq;
 using System.Threading.Tasks;
 using System.Windows.Input;
+using CoreGraphics;
 using Foundation;
 using Microsoft.Maui.Controls.Handlers.Compatibility;
 using Microsoft.Maui.Controls.Internals;
@@ -300,6 +301,25 @@ public override void DidMoveToParentViewController(UIViewController parent)
 			base.DidMoveToParentViewController(parent);
 		}
 
+		public override void ViewWillTransitionToSize(CGSize toSize, IUIViewControllerTransitionCoordinator coordinator)
+		{
+			base.ViewWillTransitionToSize(toSize, coordinator);
+
+			// On iOS 26+ the TitleView container uses autoresizing masks with an explicitly set frame,
+			// so it does not automatically resize when the navigation bar changes width during rotation.
+			// Re-apply the frame for the pushed pages' TitleViews alongside the transition.
+			if (OperatingSystem.IsIOSVersionAtLeast(26) || OperatingSystem.IsMacCatalystVersionAtLeast(26))
+			{
+				coordinator.AnimateAlongsideTransition(_ =>
+				{
+					foreach (var tracker in _trackers.Values)
+					{
+						(tracker as ShellPageRendererTracker)?.UpdateTitleViewFrameForOrientation();
+					}
+				}, null);
+			}
+		}
+
 		public override void ViewDidLoad()
 		{
 			if (_disposed)

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellSectionRootRenderer.cs

@@ -76,6 +76,17 @@ public override void ViewWillTransitionToSize(CGSize toSize, IUIViewControllerTr
 		{
 			base.ViewWillTransitionToSize(toSize, coordinator);
 			_isRotating = true;
+
+			// On iOS 26+ the TitleView container uses autoresizing masks with an explicitly set frame,
+			// so it does not automatically resize when the navigation bar changes width during rotation.
+			// Re-apply the frame alongside the transition so the TitleView fills the navigation bar.
+			if (OperatingSystem.IsIOSVersionAtLeast(26) || OperatingSystem.IsMacCatalystVersionAtLeast(26))
+			{
+				coordinator.AnimateAlongsideTransition(_ =>
+				{
+					(_tracker as ShellPageRendererTracker)?.UpdateTitleViewFrameForOrientation();
+				}, null);
+			}
 		}
 
 		public override void ViewDidLoad()

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

@@ -10,6 +10,7 @@ override Microsoft.Maui.Controls.GraphicsView.OnBindingContextChanged() -> void
 ~override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.NumberOfSections(UIKit.UICollectionView collectionView) -> nint
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellItemRenderer.ViewDidAppear(bool animated) -> void
 ~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.DidMoveToParentViewController(UIKit.UIViewController parent) -> void
+~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.ViewWillTransitionToSize(CoreGraphics.CGSize toSize, UIKit.IUIViewControllerTransitionCoordinator coordinator) -> void
 ~override Microsoft.Maui.Controls.RadioButton.OnPropertyChanged(string propertyName = null) -> void
 override Microsoft.Maui.Controls.TitleBar.OnBindingContextChanged() -> void
 override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.UpdateFlowDirection() -> void

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

@@ -10,6 +10,7 @@ override Microsoft.Maui.Controls.GraphicsView.OnBindingContextChanged() -> void
 ~override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.NumberOfSections(UIKit.UICollectionView collectionView) -> nint
 override Microsoft.Maui.Controls.Platform.Compatibility.ShellItemRenderer.ViewDidAppear(bool animated) -> void
 ~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.DidMoveToParentViewController(UIKit.UIViewController parent) -> void
+~override Microsoft.Maui.Controls.Platform.Compatibility.ShellSectionRenderer.ViewWillTransitionToSize(CoreGraphics.CGSize toSize, UIKit.IUIViewControllerTransitionCoordinator coordinator) -> void
 ~override Microsoft.Maui.Controls.RadioButton.OnPropertyChanged(string propertyName = null) -> void
 override Microsoft.Maui.Controls.TitleBar.OnBindingContextChanged() -> void
 override Microsoft.Maui.Controls.Handlers.Items2.StructuredItemsViewController2<TItemsView>.UpdateFlowDirection() -> void

src/Controls/tests/TestCases.HostApp/Issues/Issue35844.cs

@@ -0,0 +1,74 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 35844, "Shell TitleView does not resize after rotation on iOS 26+", PlatformAffected.iOS)]
+public class Issue35844Shell : Shell
+{
+	public Issue35844Shell()
+	{
+		Issue35844 contentPage = new Issue35844();
+
+		ShellContent shellContent = new ShellContent
+		{
+			Content = contentPage,
+			Route = "Issue35844"
+		};
+
+		Items.Add(shellContent);
+	}
+}
+
+public class Issue35844 : ContentPage
+{
+	public Issue35844()
+	{
+		Shell.SetTitleView(this, new Grid
+		{
+			BackgroundColor = Colors.LightBlue,
+			AutomationId = "TitleViewGrid",
+			HorizontalOptions = LayoutOptions.Fill,
+			Children =
+			{
+				new Label
+				{
+					Text = "Shell TitleView",
+					AutomationId = "TitleLabel",
+					TextColor = Colors.White,
+					FontSize = 18,
+					FontAttributes = FontAttributes.Bold,
+					VerticalOptions = LayoutOptions.Center,
+					HorizontalOptions = LayoutOptions.Center
+				}
+			}
+		});
+
+		Content = new VerticalStackLayout
+		{
+			Padding = new Thickness(20),
+			Spacing = 10,
+			Children =
+			{
+				new Label
+				{
+					Text = "Issue 35844",
+					FontSize = 20,
+					FontAttributes = FontAttributes.Bold,
+					AutomationId = "HeaderLabel",
+					HorizontalOptions = LayoutOptions.Center
+				},
+				new Label
+				{
+					Text = "Shell TitleView should fill the navigation bar width after rotation on iOS 26+.",
+					FontSize = 14,
+					AutomationId = "DescriptionLabel"
+				},
+				new Label
+				{
+					Text = "Rotate device to test",
+					AutomationId = "StatusLabel",
+					FontSize = 16,
+					TextColor = Colors.Gray
+				}
+			}
+		};
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue35844.cs

@@ -0,0 +1,46 @@
+#if TEST_FAILS_ON_WINDOWS && TEST_FAILS_ON_CATALYST // SetOrientationLandscape/Portrait is only supported on iOS and Android.
+
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue35844 : _IssuesUITest
+	{
+		public override string Issue => "Shell TitleView does not resize after rotation on iOS 26+";
+
+		public Issue35844(TestDevice device) : base(device) { }
+
+		[Test]
+		[Category(UITestCategories.Shell)]
+		public void ShellTitleViewResizesOnRotation()
+		{
+			App.WaitForElement("TitleViewGrid");
+			App.WaitForElement("StatusLabel");
+
+			// Capture portrait width
+			var portraitRect = App.WaitForElement("TitleViewGrid").GetRect();
+			var portraitWidth = portraitRect.Width;
+
+			App.SetOrientationLandscape();
+
+			// After rotation, TitleView width must change to fill the wider nav bar
+			var landscapeRect = App.WaitForElement("TitleViewGrid").GetRect();
+			var landscapeWidth = landscapeRect.Width;
+
+			Assert.That(landscapeWidth, Is.Not.EqualTo(portraitWidth).Within(100),
+				"Shell TitleView width should expand after rotating to landscape on iOS 26+");
+			Assert.That(landscapeWidth, Is.GreaterThan(portraitWidth),
+				"Shell TitleView should be wider in landscape than portrait");
+
+			// Rotate back and verify TitleView returns to original width
+			App.SetOrientationPortrait();
+
+			var finalRect = App.WaitForElement("TitleViewGrid").GetRect();
+			Assert.That(finalRect.Width, Is.EqualTo(portraitWidth).Within(5),
+				"Shell TitleView should return to original portrait width after rotating back");
+		}
+	}
+}
+#endif