Merge pull request #11418 from workgroupengineering/fixes/Issue_6263

Fixes Issue #6263

samples/ControlCatalog/ViewModels/ListBoxPageViewModel.cs

@@ -21,7 +21,7 @@ namespace ControlCatalog.ViewModels
         public ListBoxPageViewModel()
         {
             Items = new ObservableCollection<ItemModel>(Enumerable.Range(1, 10000).Select(i => GenerateItem()));
-            
+
             Selection = new SelectionModel<ItemModel>();
             Selection.Select(1);
 
@@ -34,7 +34,13 @@ namespace ControlCatalog.ViewModels
                     (t ? Avalonia.Controls.SelectionMode.Toggle : 0) |
                     (a ? Avalonia.Controls.SelectionMode.AlwaysSelected : 0));
 
-            AddItemCommand = MiniCommand.Create(() => Items.Add(GenerateItem()));
+            AddItemCommand = MiniCommand.Create(() =>
+                {
+                    var item = GenerateItem();
+                    Items.Add(item);
+                    Selection.Clear();
+                    Selection.Select(Items.Count - 1);
+                });
 
             RemoveItemCommand = MiniCommand.Create(() =>
             {
@@ -96,7 +102,7 @@ namespace ControlCatalog.ViewModels
         public MiniCommand RemoveItemCommand { get; }
         public MiniCommand SelectRandomItemCommand { get; }
 
-        private ItemModel GenerateItem() => new ItemModel(_counter ++);  
+        private ItemModel GenerateItem() => new ItemModel(_counter++);
     }
 
     /// <summary>

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -5,9 +5,7 @@ using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Xml.Linq;
 using Avalonia.Controls.Selection;
-using Avalonia.Controls.Utils;
 using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.Input.Platform;
@@ -171,7 +169,7 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         public event EventHandler<SelectionChangedEventArgs>? SelectionChanged
         {
-            add => AddHandler(SelectionChangedEvent, value); 
+            add => AddHandler(SelectionChangedEvent, value);
             remove => RemoveHandler(SelectionChangedEvent, value);
         }
 
@@ -369,7 +367,7 @@ namespace Avalonia.Controls.Primitives
         /// </summary>
         public bool WrapSelection
         {
-            get => GetValue(WrapSelectionProperty); 
+            get => GetValue(WrapSelectionProperty);
             set => SetValue(WrapSelectionProperty, value);
         }
 
@@ -382,7 +380,7 @@ namespace Avalonia.Controls.Primitives
         /// </remarks>
         protected SelectionMode SelectionMode
         {
-            get => GetValue(SelectionModeProperty); 
+            get => GetValue(SelectionModeProperty);
             set => SetValue(SelectionModeProperty, value);
         }
 
@@ -465,7 +463,10 @@ namespace Avalonia.Controls.Primitives
         protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
         {
             base.OnAttachedToVisualTree(e);
-            AutoScrollToSelectedItemIfNecessary();
+            if (Selection?.AnchorIndex is int index)
+            {
+                AutoScrollToSelectedItemIfNecessary(index);
+            }
         }
 
         /// <inheritdoc />
@@ -476,7 +477,10 @@ namespace Avalonia.Controls.Primitives
             void ExecuteScrollWhenLayoutUpdated(object? sender, EventArgs e)
             {
                 LayoutUpdated -= ExecuteScrollWhenLayoutUpdated;
-                AutoScrollToSelectedItemIfNecessary();
+                if (Selection?.AnchorIndex is int index)
+                {
+                    AutoScrollToSelectedItemIfNecessary(index);
+                }
             }
 
             if (AutoScrollToSelectedItem)
@@ -625,7 +629,10 @@ namespace Avalonia.Controls.Primitives
 
             if (change.Property == AutoScrollToSelectedItemProperty)
             {
-                AutoScrollToSelectedItemIfNecessary();
+                if (Selection?.AnchorIndex is int index)
+                {
+                    AutoScrollToSelectedItemIfNecessary(index);
+                }
             }
             else if (change.Property == SelectionModeProperty && _selection is object)
             {
@@ -909,8 +916,11 @@ namespace Avalonia.Controls.Primitives
             if (e.PropertyName == nameof(ISelectionModel.AnchorIndex))
             {
                 _hasScrolledToSelectedItem = false;
-                KeyboardNavigation.SetTabOnceActiveElement(this, ContainerFromIndex(Selection.AnchorIndex));
+                if (Selection?.AnchorIndex is int index)
-                AutoScrollToSelectedItemIfNecessary();
+                {
+                    KeyboardNavigation.SetTabOnceActiveElement(this, ContainerFromIndex(index));
+                    AutoScrollToSelectedItemIfNecessary(index);
+                }
             }
             else if (e.PropertyName == nameof(ISelectionModel.SelectedIndex) && _oldSelectedIndex != SelectedIndex)
             {
@@ -1038,7 +1048,7 @@ namespace Avalonia.Controls.Primitives
                     return value;
                 }
                 else
-                { 
+                {
                     return AvaloniaProperty.UnsetValue;
                 }
             }
@@ -1096,16 +1106,19 @@ namespace Avalonia.Controls.Primitives
             }
         }
 
-        private void AutoScrollToSelectedItemIfNecessary()
+        private void AutoScrollToSelectedItemIfNecessary(int anchorIndex)
         {
             if (AutoScrollToSelectedItem &&
                 !_hasScrolledToSelectedItem &&
                 Presenter is object &&
-                Selection.AnchorIndex >= 0 &&
+                anchorIndex >= 0 &&
                 IsAttachedToVisualTree)
             {
-                ScrollIntoView(Selection.AnchorIndex);
+                Dispatcher.UIThread.Post(state =>
-                _hasScrolledToSelectedItem = true;
+                {
+                    ScrollIntoView((int)state!);
+                    _hasScrolledToSelectedItem = true;
+                }, anchorIndex);
             }
         }
 

tests/Avalonia.Controls.UnitTests/ListBoxTests.cs

@@ -432,6 +432,8 @@ namespace Avalonia.Controls.UnitTests
                 items.Remove("1");
                 lm.ExecuteLayoutPass();
 
+                Threading.Dispatcher.UIThread.RunJobs();
+
                 Assert.Equal("30", target.ContainerFromIndex(items.Count - 1).DataContext);
                 Assert.Equal("29", target.ContainerFromIndex(items.Count - 2).DataContext);
                 Assert.Equal("28", target.ContainerFromIndex(items.Count - 3).DataContext);
@@ -457,8 +459,13 @@ namespace Avalonia.Controls.UnitTests
 
                 Prepare(target);
 
+                Threading.Dispatcher.UIThread.RunJobs();
+
                 // First an item that is not index 0 must be selected.
                 _mouse.Click(target.Presenter.Panel.Children[1]);
+
+                Threading.Dispatcher.UIThread.RunJobs();
+
                 Assert.Equal(1, target.Selection.AnchorIndex);
 
                 // We're going to be clicking on item 9.
@@ -471,6 +478,7 @@ namespace Avalonia.Controls.UnitTests
                 // into view due to SelectionMode.AlwaysSelected.
                 target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) =>
                 {
+
                     Assert.Same(item, e.TargetObject);
                     ++raised;
                 });
@@ -478,6 +486,8 @@ namespace Avalonia.Controls.UnitTests
                 // Click item 9.
                 _mouse.Click(item);
 
+                Threading.Dispatcher.UIThread.RunJobs();
+
                 Assert.Equal(1, raised);
             }
         }
@@ -744,6 +754,8 @@ namespace Avalonia.Controls.UnitTests
             items.Reverse();
             Layout(target);
 
+            Threading.Dispatcher.UIThread.RunJobs();
+
             realized = target.GetRealizedContainers()
                 .Cast<ListBoxItem>()
                 .Select(x => (string)x.DataContext)

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

@@ -1536,7 +1536,7 @@ namespace Avalonia.Controls.UnitTests.Primitives
             Prepare(target);
             target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
             target.SelectedIndex = 2;
-
+            Threading.Dispatcher.UIThread.RunJobs();
             Assert.True(raised);
         }
 
@@ -1561,7 +1561,7 @@ namespace Avalonia.Controls.UnitTests.Primitives
             target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
             target.SelectedIndex = 2;
             Prepare(target);
-
+            Threading.Dispatcher.UIThread.RunJobs();
             Assert.True(raised);
         }
 
@@ -1632,7 +1632,7 @@ namespace Avalonia.Controls.UnitTests.Primitives
             root.Child = null;
             target.SelectedIndex = 1;
             root.Child = target;
-
+            Threading.Dispatcher.UIThread.RunJobs();
             Assert.True(raised);
         }
 
@@ -1689,11 +1689,11 @@ namespace Avalonia.Controls.UnitTests.Primitives
             var raised = false;
             target.AddHandler(Control.RequestBringIntoViewEvent, (s, e) => raised = true);
             target.SelectedIndex = 2;
-
+            Threading.Dispatcher.UIThread.RunJobs();
             Assert.False(raised);
 
             target.AutoScrollToSelectedItem = true;
-
+            Threading.Dispatcher.UIThread.RunJobs();
             Assert.True(raised);
         }