Merge pull request #18542 from unoplatform/mergify/bp/release/stable/…

…5.5/pr-18492

fix(ios): Tabview Selection when Bindings items (backport #18492)

src/Uno.UI.RuntimeTests/Tests/Microsoft_UI_Xaml_Controls/Given_TabView.cs

@@ -114,4 +114,107 @@ public async Task When_Tab_Removed()
 		Assert.AreEqual(0, SUT.SelectedIndex);
 		Assert.AreEqual("Tab 2", ((TabViewItem)SUT.TabItems[0]).Header);
 	}
+
+	[TestMethod]
+	public async Task When_SelectedItem_Changed()
+	{
+		var SUT = new TabView
+		{
+			TabItems =
+			{
+				new TabViewItem { Header = "Tab 1" },
+				new TabViewItem { Header = "Tab 2" }
+			}
+		};
+
+		await UITestHelper.Load(SUT);
+
+		Assert.AreEqual(0, SUT.SelectedIndex);
+
+		SUT.SelectedItem = SUT.TabItems[1];
+
+		await WindowHelper.WaitForIdle();
+
+		Assert.AreEqual(1, SUT.SelectedIndex);
+	}
+
+	[TestMethod]
+	public async Task When_DataBinding()
+	{
+		var vm = new ViewModel();
+		var SUT = new TabView();
+
+		SUT.SetBinding(TabView.TabItemsSourceProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("TabItems") });
+		SUT.SetBinding(TabView.SelectedItemProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("SelectedItem"), Mode = Microsoft.UI.Xaml.Data.BindingMode.TwoWay });
+
+		SUT.DataContext = vm;
+
+		await UITestHelper.Load(SUT);
+
+		Assert.AreEqual(2, SUT.TabItems.Count);
+		Assert.AreEqual(0, SUT.SelectedIndex);
+	}
+
+	[TestMethod]
+	public async Task When_SelectedItem_Changed_Binding()
+	{
+		var vm = new ViewModel();
+		var SUT = new TabView();
+
+		SUT.SetBinding(TabView.TabItemsSourceProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("TabItems") });
+		SUT.SetBinding(TabView.SelectedItemProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("SelectedItem"), Mode = Microsoft.UI.Xaml.Data.BindingMode.TwoWay });
+
+		SUT.DataContext = vm;
+
+		vm.SelectedItem = vm.TabItems[1];
+
+		await UITestHelper.Load(SUT);
+
+		Assert.AreEqual(1, SUT.SelectedIndex);
+	}
+
+	[TestMethod]
+	public async Task When_AddingTab_While_Binding()
+	{
+		var SUT = new TabView();
+
+		SUT.SetBinding(TabView.TabItemsSourceProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("TabItems") });
+		SUT.SetBinding(TabView.SelectedItemProperty, new Microsoft.UI.Xaml.Data.Binding() { Path = new("SelectedItem"), Mode = Microsoft.UI.Xaml.Data.BindingMode.TwoWay });
+
+		SUT.DataContext = new ViewModel(addTab: true);
+
+		await UITestHelper.Load(SUT);
+
+		// It should select the newly added tab
+		Assert.AreEqual(2, SUT.SelectedIndex);
+
+		var tabviewItem = SUT.ContainerFromItem(SUT.SelectedItem) as TabViewItem;
+		Assert.IsTrue(tabviewItem.ActualWidth > 0, "TabViewItem should have a non-zero width.");
+		Assert.IsTrue(tabviewItem.ActualHeight > 0, "TabViewItem should have a non-zero height.");
+	}
+}
+
+public class ViewModel : ViewModelBase
+{
+	public ViewModel(bool addTab = false)
+	{
+		if (addTab)
+		{
+			TabItems.Add(new TabViewItem { Header = "Main Tab", Content = "Main Content" });
+			SelectedItem = TabItems[^1];
+		}
+	}
+	private TabViewItem _selectedItem;
+
+	public TabViewItem SelectedItem
+	{
+		get => _selectedItem;
+		set => SetAndRaiseIfChanged(ref _selectedItem, value);
+	}
+
+	public ObservableCollection<TabViewItem> TabItems { get; } = new ObservableCollection<TabViewItem>
+	{
+		new TabViewItem { Header = "Tab 1", Content = "Content 1" },
+		new TabViewItem { Header = "Tab 2", Content = "Content 2" }
+	};
 }

src/Uno.UI/Microsoft/UI/Xaml/Controls/TabView/TabView.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 // MUX Reference TabView.cpp, commit ed31e13
 
@@ -551,7 +551,9 @@ private void OnListViewLoaded(object sender, RoutedEventArgs args)
 					TabItems = lvItems;
 				}
 
-				if (ReadLocalValue(SelectedItemProperty) != DependencyProperty.UnsetValue)
+				// ReadLocalValue() is not returning UnsetValue even though SelectedItem is not yet set
+				if (ReadLocalValue(SelectedItemProperty) != DependencyProperty.UnsetValue
+					&& SelectedItem is not null)
 				{
 					UpdateSelectedItem();
 				}
@@ -1268,27 +1270,17 @@ public object ItemFromContainer(DependencyObject container)
 
 		private int GetItemCount()
 		{
-			var itemsSource = TabItemsSource;
-			if (itemsSource != null)
+			if (TabItemsSource is { } itemsSource)
 			{
-				var iterable = itemsSource as IEnumerable;
-				if (iterable != null)
+				if (itemsSource is IEnumerable iterable)
 				{
-					//int i = 1;
-					//var iter = iterable.First();
-					//while (iter.MoveNext())
-					//{
-					//	i++;
-					//}
-					//return i;
 					return iterable.Count();
 				}
 				return 0;
 			}
-
 			else
 			{
-				return (int)TabItems.Count;
+				return TabItems.Count;
 			}
 		}
 

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.managed.cs

@@ -111,8 +111,10 @@ private void ScrollIntoViewFastPath(UIElement element, ScrollIntoViewAlignment a
 #endif
 					);
 
+				var orientation = ItemsPanelRoot?.PhysicalOrientation ?? Orientation.Vertical;
+
 				var (elementOffset, elementLength, presenterOffset, presenterViewportLength) =
-					ItemsPanelRoot.PhysicalOrientation is Orientation.Vertical
+					orientation is Orientation.Vertical
 						? (offsetXY.Y, element.ActualSize.Y, presenter.VerticalOffset, presenter.ViewportHeight)
 						: (offsetXY.X, element.ActualSize.X, presenter.HorizontalOffset, presenter.ViewportWidth);
 
@@ -130,7 +132,7 @@ ItemsPanelRoot.PhysicalOrientation is Orientation.Vertical
 					? elementOffset - presenterViewportLength + elementLength
 					: elementOffset;
 
-				if (ItemsPanelRoot.PhysicalOrientation is Orientation.Vertical)
+				if (orientation is Orientation.Vertical)
 				{
 					sv.ScrollToVerticalOffset(newOffset);
 				}

src/Uno.UI/UI/Xaml/Controls/Primitives/Selector.cs

@@ -193,7 +193,13 @@ internal virtual void OnSelectedItemChanged(object oldSelectedItem, object selec
 #if !IS_UNIT_TESTS
 			if (newIndex != -1 && IsInLiveTree)
 			{
-				if (this is ListViewBase lvb)
+				if (this is ListViewBase lvb
+#if __IOS__
+					// workaround to prevent scrolling when it is not ready
+					// without this, the ios TabView could render blank if the selection happens too early.
+					&& ContainerFromIndex(newIndex) is FrameworkElement { IsLoaded: true }
+#endif
+				)
 				{
 #if __IOS__ || __ANDROID__
 					lvb.InstantScrollToIndex(newIndex);