Added failing tests for #11119.

tests/Avalonia.Controls.UnitTests/CarouselTests.cs

@@ -261,6 +261,71 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Can_Move_Forward_Back_Forward()
+        {
+            using var app = Start();
+            var items = new[] { "foo", "bar" };
+            var target = new Carousel
+            {
+                Template = CarouselTemplate(),
+                ItemsSource = items,
+            };
+
+            Prepare(target);
+
+            target.SelectedIndex = 1;
+            Layout(target);
+
+            Assert.Equal(1, target.SelectedIndex);
+
+            target.SelectedIndex = 0;
+            Layout(target);
+
+            Assert.Equal(0, target.SelectedIndex);
+
+            target.SelectedIndex = 1;
+            Layout(target);
+
+            Assert.Equal(1, target.SelectedIndex);
+        }
+
+        [Fact]
+        public void Can_Move_Forward_Back_Forward_With_Control_Items()
+        {
+            // Issue #11119
+            using var app = Start();
+            var items = new[] { new Canvas(), new Canvas() };
+            var target = new Carousel
+            {
+                Template = CarouselTemplate(),
+                ItemsSource = items,
+            };
+
+            Prepare(target);
+
+            target.SelectedIndex = 1;
+            Layout(target);
+
+            Assert.Equal(1, target.SelectedIndex);
+
+            target.SelectedIndex = 0;
+            Layout(target);
+
+            Assert.Equal(0, target.SelectedIndex);
+
+            target.SelectedIndex = 1;
+            target.PropertyChanged += (s, e) =>
+            {
+                if (e.Property == Carousel.SelectedIndexProperty)
+                {
+                }
+            };
+            Layout(target);
+
+            Assert.Equal(1, target.SelectedIndex);
+        }
+
         private static IDisposable Start() => UnitTestApplication.Start(TestServices.MockPlatformRenderInterface);
 
         private static void Prepare(Carousel target)

tests/Avalonia.Controls.UnitTests/Primitives/SelectingItemsControlTests_Multiple.cs

@@ -1024,6 +1024,56 @@ namespace Avalonia.Controls.UnitTests.Primitives
             Assert.Equal(new[] { 15 }, SelectedContainers(target));
         }
 
+        [Fact]
+        public void Can_Change_Selection_For_Containers_Outside_Of_Viewport()
+        {
+            // Issue #11119
+            using var app = Start();
+            var items = Enumerable.Range(0, 100).Select(x => new TestContainer 
+            { 
+                Content = $"Item {x}",
+                Height = 100,
+            }).ToList();
+
+            // Create a SelectingItemsControl with a virtualizing stack panel.
+            var target = CreateTarget(itemsSource: items, virtualizing: true);
+            target.AutoScrollToSelectedItem = false;
+
+            var panel = Assert.IsType<VirtualizingStackPanel>(target.ItemsPanelRoot);
+            var scroll = panel.FindAncestorOfType<ScrollViewer>()!;
+
+            // Select item 1.
+            target.SelectedIndex = 1;
+
+            // Scroll item 1 and 2 out of view.
+            scroll.Offset = new(0, 1000);
+            Layout(target);
+
+            Assert.Equal(10, panel.FirstRealizedIndex);
+            Assert.Equal(19, panel.LastRealizedIndex);
+
+            // Select item 2 now that items 1 and 2 are both unrealized.
+            target.SelectedIndex = 2;
+
+            // The selection should be updated.
+            Assert.Empty(SelectedContainers(target));
+            Assert.Equal(2, target.SelectedIndex);
+            Assert.Same(items[2], target.SelectedItem);
+            Assert.Equal(new[] { 2 }, target.Selection.SelectedIndexes);
+            Assert.Equal(new[] { items[2] }, target.Selection.SelectedItems);
+
+            // Scroll selected item back into view.
+            scroll.Offset = new(0, 0);
+            Layout(target);
+
+            // The selection should be preserved.
+            Assert.Equal(new[] { 2 }, SelectedContainers(target));
+            Assert.Equal(2, target.SelectedIndex);
+            Assert.Same(items[2], target.SelectedItem);
+            Assert.Equal(new[] { 2 }, target.Selection.SelectedIndexes);
+            Assert.Equal(new[] { items[2] }, target.Selection.SelectedItems);
+        }
+
         [Fact]
         public void Selection_State_Change_On_Unrealized_Item_Is_Respected_With_IsSelected_Binding()
         {
@@ -1197,7 +1247,7 @@ namespace Avalonia.Controls.UnitTests.Primitives
             {
                 Setters =
                 {
-                    new Setter(TreeView.TemplateProperty, CreateTestContainerTemplate()),
+                    new Setter(TestContainer.TemplateProperty, CreateTestContainerTemplate()),
                 },
             };
         }