Fix null reference exception in KeyboardAutoManagerScroll when UIWindow is null

src/Controls/samples/Controls.Sample.UITests/Issues/Issue21726.xaml

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue21726"
+             Title="Issue21726">
+    <VerticalStackLayout>
+        <Button Text="AddVC" AutomationId="AddVC" Clicked="AddVC"/>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue21726.xaml.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Linq;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+using System.Threading.Tasks;
+
+namespace Maui.Controls.Sample.Issues;
+
+[XamlCompilation(XamlCompilationOptions.Compile)]
+[Issue(IssueTracker.Github, 21726, "Modal with a bottom sheet should not crash iOS Keyboard Scroll", PlatformAffected.iOS)]
+public partial class Issue21726 : ContentPage
+{
+	public Issue21726()
+	{
+		InitializeComponent();
+	}
+
+	void AddVC (object sender, EventArgs e)
+	{
+#if IOS
+		var window = UIKit.UIApplication.SharedApplication
+        .ConnectedScenes
+        .OfType<UIKit.UIWindowScene>()
+        .SelectMany(s => s.Windows)
+        .FirstOrDefault(w => w.IsKeyWindow);
+
+		var rootVC = window?.RootViewController;
+		while (rootVC?.PresentedViewController != null)
+		{
+			rootVC = rootVC.PresentedViewController;
+		}
+
+		if (rootVC is not null) {
+			var testVC = new TestViewController();
+
+			var testNC = new UIKit.UINavigationController(testVC)
+			{
+				ModalPresentationStyle = UIKit.UIModalPresentationStyle.FullScreen
+			};
+
+			rootVC.PresentViewController(testNC, true, null);
+		}
+#endif
+	}
+
+#if IOS
+	public class TestViewController: UIKit.UIViewController {
+
+		UIKit.UITextField TextField1;
+		UIKit.UIButton Button1;
+
+		public override void ViewDidLoad() {
+			base.ViewDidLoad();
+
+			View.BackgroundColor = UIKit.UIColor.White;
+
+			TextField1 = new UIKit.UITextField(new CoreGraphics.CGRect(20, 120, 200, 20))
+			{
+				Placeholder = "TextField1",
+				BorderStyle = UIKit.UITextBorderStyle.RoundedRect,
+				AccessibilityIdentifier = "TextField1"
+			};
+
+			Button1 = new UIKit.UIButton(new CoreGraphics.CGRect(20, 320, 200, 40));
+			Button1.SetTitle("Dismiss", UIKit.UIControlState.Normal);
+			Button1.BackgroundColor = UIKit.UIColor.SystemBlue;
+			Button1.AccessibilityIdentifier = "Button1";
+			Button1.TouchUpInside += (sender, e) => {
+				DismissViewController(true, null);
+			};
+
+			View.AddSubview(TextField1);
+			View.AddSubview(Button1);
+		}
+	}
+#endif
+}

src/Controls/tests/UITests/Tests/Issues/Issue21726.cs

@@ -0,0 +1,28 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+    public class Issue21726 : _IssuesUITest
+    {
+        public Issue21726(TestDevice device) : base(device)
+        {
+        }
+
+        public override string Issue => "Modal with a bottom sheet should not crash iOS Keyboard Scroll";
+
+        [Test]
+        public void PushViewControllerWithNullWindow()
+        {
+            this.IgnoreIfPlatforms([TestDevice.Android, TestDevice.Mac, TestDevice.Windows]);
+
+            App.WaitForElement("AddVC");
+            App.Click("AddVC");
+            App.WaitForElement("TextField1").Click();
+            App.WaitForElement("Button1").Click();
+            var mainPageElement = App.WaitForElement("AddVC");
+            Assert.NotNull(mainPageElement);
+        }
+    }
+}

src/Core/src/Platform/iOS/KeyboardAutoManagerScroll.cs

@@ -299,7 +299,8 @@ internal static async Task AdjustPositionDebounce()
 	internal static void AdjustPosition()
 	{
 		if (ContainerView is null
-			|| (View is not UITextField && View is not UITextView))
+			|| (View is not UITextField && View is not UITextView)
+			|| !View.IsDescendantOfView(ContainerView))
 		{
 			IsKeyboardAutoScrollHandling = false;
 			return;
@@ -311,6 +312,12 @@ internal static void AdjustPosition()
 		var rootViewOrigin = new CGPoint(ContainerView.Frame.GetMinX(), ContainerView.Frame.GetMinY());
 		var window = ContainerView.Window;
 
+		if (window is null)
+		{
+			IsKeyboardAutoScrollHandling = false;
+			return;
+		}
+
 		var intersectRect = CGRect.Intersect(KeyboardFrame, window.Frame);
 		var kbSize = intersectRect == CGRect.Empty ? new CGSize(KeyboardFrame.Width, 0) : intersectRect.Size;