[Windows] Fix Preserve ScrollView offsets when Orientation changes to Neither

src/Controls/tests/TestCases.HostApp/Issues/Issue34671.cs

@@ -0,0 +1,287 @@
+using System.Globalization;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 34671, "[Windows] ScrollView offsets do not preserve when Orientation changes to Neither", PlatformAffected.UWP)]
+public class Issue34671 : ContentPage
+{
+	const double ReproScrollX = 700;
+	const double ReproScrollY = 480;
+	readonly Label _orientationLabel;
+	readonly Label _offsetLabel;
+	readonly Label _lastActionLabel;
+	readonly ScrollView _bugScrollView;
+	string _lastAction = string.Empty;
+
+	public Issue34671()
+	{
+		Title = "ScrollView Orientation Repro";
+
+		_orientationLabel = new Label
+		{
+			AutomationId = "OrientationLabel",
+			Text = "Orientation: Both"
+		};
+
+		_offsetLabel = new Label
+		{
+			AutomationId = "OffsetLabel",
+			Text = "ScrollX: 0 | ScrollY: 0"
+		};
+
+		_lastActionLabel = new Label
+		{
+			AutomationId = "LastActionLabel",
+			Text = "Action: launch the app and tap 'Scroll To Repro Offset'."
+		};
+
+		_bugScrollView = new ScrollView
+		{
+			AutomationId = "BugScrollView",
+			Orientation = ScrollOrientation.Both,
+			Content = CreateScrollContent()
+		};
+		_bugScrollView.Scrolled += OnScrollViewScrolled;
+
+		Content = new Grid
+		{
+			Padding = 16,
+			RowSpacing = 12,
+			RowDefinitions =
+			{
+				new RowDefinition(GridLength.Auto),
+				new RowDefinition(GridLength.Auto),
+				new RowDefinition(GridLength.Auto),
+				new RowDefinition(GridLength.Star)
+			},
+			Children =
+			{
+				new Label
+				{
+					Text = "Repro for dotnet/maui#34671: scroll away from the origin, then set Orientation to Neither. On iOS, ScrollX and ScrollY reset to 0 instead of being preserved.",
+					LineBreakMode = LineBreakMode.WordWrap
+				}.Row(0),
+				new VerticalStackLayout
+				{
+					Spacing = 6,
+					Children =
+					{
+						new HorizontalStackLayout
+						{
+							Spacing = 8,
+							Children =
+							{
+								new Button
+								{
+									Text = "Scroll To Repro Offset",
+									AutomationId = "ScrollToReproOffsetButton"
+								}.Assign(out var scrollToReproOffsetButton),
+								new Button
+								{
+									Text = "Set Both",
+									AutomationId = "SetBothButton"
+								}.Assign(out var setBothButton),
+								new Button
+								{
+									Text = "Set Neither",
+									AutomationId = "SetNeitherButton"
+								}.Assign(out var setNeitherButton),
+								new Button
+								{
+									Text = "Reset",
+									AutomationId = "ResetButton"
+								}.Assign(out var resetButton),
+							}
+						},
+						_orientationLabel,
+						_offsetLabel,
+						_lastActionLabel
+					}
+				}.Row(1),
+				new Border
+				{
+					StrokeThickness = 1,
+					Stroke = Color.FromArgb("#A0A0A0"),
+					Padding = 10,
+					Background = Color.FromArgb("#F7F7F7"),
+					Content = new Label
+					{
+						Text = "Expected: changing to Neither should preserve the current scroll position. Actual bug: the offset snaps back to the origin."
+					}
+				}.Row(2),
+				new Border
+				{
+					StrokeThickness = 1,
+					Stroke = Color.FromArgb("#202020"),
+					Background = Color.FromArgb("#FFFFFF"),
+					HeightRequest = 360,
+					Content = _bugScrollView
+				}.Row(3)
+			}
+		};
+
+		scrollToReproOffsetButton.Clicked += OnScrollToSampleClicked;
+		setBothButton.Clicked += OnSetBothClicked;
+		setNeitherButton.Clicked += OnSetNeitherClicked;
+		resetButton.Clicked += OnResetClicked;
+
+		RefreshState("Launch the app, tap 'Scroll To Repro Offset', then tap 'Set Neither'.");
+	}
+
+	Grid CreateScrollContent()
+	{
+		return new Grid
+		{
+			WidthRequest = 1400,
+			HeightRequest = 1100,
+			Background = Color.FromArgb("#FFF8E7"),
+			RowDefinitions =
+			{
+				new RowDefinition(220),
+				new RowDefinition(220),
+				new RowDefinition(220),
+				new RowDefinition(220),
+				new RowDefinition(220)
+			},
+			ColumnDefinitions =
+			{
+				new ColumnDefinition(280),
+				new ColumnDefinition(280),
+				new ColumnDefinition(280),
+				new ColumnDefinition(280),
+				new ColumnDefinition(280)
+			},
+			Children =
+			{
+				new BoxView { Margin = 16, Color = Color.FromArgb("#F94144"), Opacity = 0.35 }.Row(0).Column(0),
+				new BoxView { Margin = 16, Color = Color.FromArgb("#F3722C"), Opacity = 0.35 }.Row(0).Column(4),
+				new BoxView { Margin = 16, Color = Color.FromArgb("#90BE6D"), Opacity = 0.45 }.Row(2).Column(2),
+				new BoxView { Margin = 16, Color = Color.FromArgb("#577590"), Opacity = 0.35 }.Row(4).Column(0),
+				new BoxView { Margin = 16, Color = Color.FromArgb("#277DA1"), Opacity = 0.35 }.Row(4).Column(4),
+				new Border
+				{
+					Margin = 20,
+					Padding = 12,
+					Background = Color.FromArgb("#FFFFFF"),
+					Stroke = Color.FromArgb("#222222"),
+					Content = new Label
+					{
+						Text = "Origin (0,0)",
+						FontAttributes = FontAttributes.Bold
+					}
+				}.Row(0).Column(0),
+				new Border
+				{
+					Margin = 20,
+					Padding = 12,
+					Background = Color.FromArgb("#FFFFFF"),
+					Stroke = Color.FromArgb("#222222"),
+					Content = new VerticalStackLayout
+					{
+						Spacing = 6,
+						Children =
+						{
+							new Label
+							{
+								Text = "Target zone",
+								FontAttributes = FontAttributes.Bold
+							},
+							new Label
+							{
+								Text = "Tap 'Scroll To Repro Offset', then 'Set Neither'."
+							}
+						}
+					}
+				}.Row(2).Column(2),
+				new Border
+				{
+					Margin = 20,
+					Padding = 12,
+					Background = Color.FromArgb("#FFFFFF"),
+					Stroke = Color.FromArgb("#222222"),
+					Content = new Label
+					{
+						Text = "Bottom-right marker",
+						FontAttributes = FontAttributes.Bold
+					}
+				}.Row(4).Column(4)
+			}
+		};
+	}
+
+	async void OnScrollToSampleClicked(object sender, EventArgs e)
+	{
+		var orientationChanged = _bugScrollView.Orientation != ScrollOrientation.Both;
+		_bugScrollView.Orientation = ScrollOrientation.Both;
+
+		if (orientationChanged)
+		{
+			await Task.Delay(100);
+		}
+
+		await _bugScrollView.ScrollToAsync(ReproScrollX, ReproScrollY, false);
+		await Task.Delay(50);
+		RefreshState($"Scrolled to approx. X={ReproScrollX:0}, Y={ReproScrollY:0}.");
+	}
+
+	void OnSetBothClicked(object sender, EventArgs e)
+	{
+		_bugScrollView.Orientation = ScrollOrientation.Both;
+		RefreshState("Orientation set to Both.");
+	}
+
+	async void OnSetNeitherClicked(object sender, EventArgs e)
+	{
+		var beforeX = _bugScrollView.ScrollX;
+		var beforeY = _bugScrollView.ScrollY;
+
+		_bugScrollView.Orientation = ScrollOrientation.Neither;
+
+		await Task.Delay(100);
+		RefreshState($"Set Orientation to Neither. Before: X={beforeX:0.##}, Y={beforeY:0.##}. After: X={_bugScrollView.ScrollX:0.##}, Y={_bugScrollView.ScrollY:0.##}.");
+	}
+
+	async void OnResetClicked(object sender, EventArgs e)
+	{
+		_bugScrollView.Orientation = ScrollOrientation.Both;
+		await _bugScrollView.ScrollToAsync(0, 0, false);
+		RefreshState("Reset orientation to Both and scrolled back to the origin.");
+	}
+
+	void OnScrollViewScrolled(object sender, ScrolledEventArgs e)
+	{
+		RefreshState(_lastAction);
+	}
+
+	void RefreshState(string action)
+	{
+		_lastAction = action ?? string.Empty;
+		_orientationLabel.Text = $"Orientation: {_bugScrollView.Orientation}";
+		_offsetLabel.Text = $"ScrollX: {_bugScrollView.ScrollX.ToString("0.##", CultureInfo.InvariantCulture)} | ScrollY: {_bugScrollView.ScrollY.ToString("0.##", CultureInfo.InvariantCulture)}";
+		_lastActionLabel.Text = $"Action: {_lastAction}";
+	}
+}
+
+static class Issue34671ViewExtensions
+{
+	public static TView Row<TView>(this TView view, int row)
+		where TView : View
+	{
+		Grid.SetRow(view, row);
+		return view;
+	}
+
+	public static TView Column<TView>(this TView view, int column)
+		where TView : View
+	{
+		Grid.SetColumn(view, column);
+		return view;
+	}
+
+	public static TView Assign<TView>(this TView view, out TView assigned)
+		where TView : View
+	{
+		assigned = view;
+		return view;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue34671.cs

@@ -0,0 +1,41 @@
+#if WINDOWS || ANDROID // Existing PR for iOS : https://github.com/dotnet/maui/pull/34672
+using System.Globalization;
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue34671 : _IssuesUITest
+{
+	public override string Issue => "[Windows] ScrollView offsets do not preserve when Orientation changes to Neither";
+
+	public Issue34671(TestDevice device) : base(device) { }
+
+	[Test]
+	[Category(UITestCategories.ScrollView)]
+	public void Issue34671ScrollPositionIsPreservedWhenOrientationChangesToNeither()
+	{
+		App.WaitForElement("ScrollToReproOffsetButton");
+		App.Tap("ScrollToReproOffsetButton");
+		App.WaitForTextToBePresentInElement("LastActionLabel", "Scrolled to approx");
+		App.WaitForElement("SetNeitherButton");
+		App.Tap("SetNeitherButton");
+
+		var offsetText = App.WaitForElement("OffsetLabel").GetText()
+			?? throw new InvalidOperationException("OffsetLabel text was null.");
+		var offsetParts = offsetText.Split('|', StringSplitOptions.TrimEntries);
+		var scrollXText = offsetParts[0]
+			.Replace("ScrollX:", string.Empty, StringComparison.Ordinal)
+			.Trim();
+		var scrollYText = offsetParts[1]
+			.Replace("ScrollY:", string.Empty, StringComparison.Ordinal)
+			.Trim();
+		var scrollX = double.Parse(scrollXText, CultureInfo.InvariantCulture);
+		var scrollY = double.Parse(scrollYText, CultureInfo.InvariantCulture);
+
+		Assert.That(scrollX, Is.GreaterThan(0d), "ScrollX should remain non-zero after setting orientation to Neither.");
+		Assert.That(scrollY, Is.GreaterThan(0d), "ScrollY should remain non-zero after setting orientation to Neither.");
+	}
+}
+#endif

src/Core/src/Platform/Windows/ScrollViewerExtensions.cs

@@ -20,10 +20,21 @@ public static void UpdateScrollBarVisibility(this ScrollViewer scrollViewer, Scr
 		{
 			if (orientation == ScrollOrientation.Neither)
 			{
-				scrollViewer.HorizontalScrollBarVisibility = scrollViewer.VerticalScrollBarVisibility = WScrollBarVisibility.Disabled;
+				// Use Hidden (not Disabled) so WinUI keeps the current ContentOffset instead of
+				// resetting it to (0,0). ScrollMode.Disabled prevents further user scrolling while
+				// the orientation is Neither.
+				scrollViewer.HorizontalScrollBarVisibility = WScrollBarVisibility.Hidden;
+				scrollViewer.VerticalScrollBarVisibility = WScrollBarVisibility.Hidden;
+				scrollViewer.HorizontalScrollMode = ScrollMode.Disabled;
+				scrollViewer.VerticalScrollMode = ScrollMode.Disabled;
 				return;
 			}
 
+			// When leaving Neither, restore scroll modes to Auto so that they follow
+			// the ScrollBarVisibility settings applied below.
+			scrollViewer.HorizontalScrollMode = ScrollMode.Auto;
+			scrollViewer.VerticalScrollMode = ScrollMode.Auto;
+
 			if (visibility == ScrollBarVisibility.Default)
 			{
 				// If the user has not explicitly set a horizontal scroll bar visibility, then the orientation will