Allow selection of elements outside viewport.

Allow selection of elements outside viewport when using keyboard to select.

src/Avalonia.Controls/VirtualizingStackPanel.cs

@@ -70,8 +70,8 @@ namespace Avalonia.Controls
         private ScrollViewer? _scrollViewer;
         private Rect _viewport = s_invalidViewport;
         private Dictionary<object, Stack<Control>>? _recyclePool;
-        private Control? _unrealizedFocusedElement;
-        private int _unrealizedFocusedIndex = -1;
+        private Control? _outOfViewportFocusedElement;
+        private int _outOfViewportFocusedIndex = -1;
 
         public VirtualizingStackPanel()
         {
@@ -332,14 +332,21 @@ namespace Avalonia.Controls
         {
             if (index < 0 || index >= Items.Count)
                 return null;
-            if (_realizedElements?.GetElement(index) is { } realized)
+            if (GetRealizedElement(index) is { } realized)
                 return realized;
             if (Items[index] is Control c && c.GetValue(RecycleKeyProperty) == s_itemIsItsOwnContainer)
                 return c;
             return null;
         }
 
-        protected internal override int IndexFromContainer(Control container) => _realizedElements?.GetIndex(container) ?? -1;
+        protected internal override int IndexFromContainer(Control container)
+        {
+            if (container == _scrollToElement)
+                return _scrollToIndex;
+            if (container == _outOfViewportFocusedElement)
+                return _outOfViewportFocusedIndex;
+            return _realizedElements?.GetIndex(container) ?? -1;
+        }
 
         protected internal override Control? ScrollIntoView(int index)
         {
@@ -590,6 +597,8 @@ namespace Avalonia.Controls
         {
             if (_scrollToIndex == index)
                 return _scrollToElement;
+            if (_outOfViewportFocusedIndex == index)
+                return _outOfViewportFocusedElement;
             return _realizedElements?.GetElement(index);
         }
 
@@ -621,15 +630,6 @@ namespace Avalonia.Controls
 
             var generator = ItemContainerGenerator!;
 
-            if (_unrealizedFocusedIndex == index && _unrealizedFocusedElement is not null)
-            {
-                var element = _unrealizedFocusedElement;
-                _unrealizedFocusedElement.LostFocus -= OnUnrealizedFocusedElementLostFocus;
-                _unrealizedFocusedElement = null;
-                _unrealizedFocusedIndex = -1;
-                return element;
-            }
-
             if (_recyclePool?.TryGetValue(recycleKey, out var recyclePool) == true && recyclePool.Count > 0)
             {
                 var recycled = recyclePool.Pop();
@@ -672,9 +672,9 @@ namespace Avalonia.Controls
             }
             else if (element.IsKeyboardFocusWithin)
             {
-                _unrealizedFocusedElement = element;
-                _unrealizedFocusedIndex = index;
-                _unrealizedFocusedElement.LostFocus += OnUnrealizedFocusedElementLostFocus;
+                _outOfViewportFocusedElement = element;
+                _outOfViewportFocusedIndex = index;
+                _outOfViewportFocusedElement.LostFocus += OnUnrealizedFocusedElementLostFocus;
             }
             else
             {
@@ -744,13 +744,13 @@ namespace Avalonia.Controls
 
         private void OnUnrealizedFocusedElementLostFocus(object? sender, RoutedEventArgs e)
         {
-            if (_unrealizedFocusedElement is null || sender != _unrealizedFocusedElement)
+            if (_outOfViewportFocusedElement is null || sender != _outOfViewportFocusedElement)
                 return;
 
-            _unrealizedFocusedElement.LostFocus -= OnUnrealizedFocusedElementLostFocus;
-            RecycleElement(_unrealizedFocusedElement, _unrealizedFocusedIndex);
-            _unrealizedFocusedElement = null;
-            _unrealizedFocusedIndex = -1;
+            _outOfViewportFocusedElement.LostFocus -= OnUnrealizedFocusedElementLostFocus;
+            RecycleElement(_outOfViewportFocusedElement, _outOfViewportFocusedIndex);
+            _outOfViewportFocusedElement = null;
+            _outOfViewportFocusedIndex = -1;
         }
 
         /// <inheritdoc/>

tests/Avalonia.Controls.UnitTests/ListBoxTests.cs

@@ -893,6 +893,37 @@ namespace Avalonia.Controls.UnitTests
             Assert.True(target.ContainerFromIndex(1).IsFocused);
         }
 
+        [Fact]
+        public void Down_Key_Brings_Unrealized_Selection_Into_View()
+        {
+            using var app = UnitTestApplication.Start(TestServices.RealFocus);
+            var items = Enumerable.Range(0, 100).Select(x => $"Item {x}").ToArray();
+            var target = new ListBox
+            {
+                Template = ListBoxTemplate(),
+                ItemsSource = items,
+                ItemTemplate = new FuncDataTemplate<string>((x, _) => new TextBlock { Width = 20, Height = 10 }),
+                Width = 100,
+                Height = 100,
+                SelectedIndex = 0,
+            };
+
+            Prepare(target);
+
+            target.ContainerFromIndex(0)!.Focus();
+            target.Scroll.Offset = new Vector(0, 100);
+            Layout(target);
+
+            var panel = (VirtualizingStackPanel)target.ItemsPanelRoot;
+            Assert.Equal(10, panel.FirstRealizedIndex);
+
+            RaiseKeyEvent(target, Key.Down);
+
+            Assert.Equal(1, target.SelectedIndex);
+            Assert.True(target.ContainerFromIndex(1).IsFocused);
+            Assert.Equal(new Vector(0, 10), target.Scroll.Offset);
+        }
+
         [Fact]
         public void WrapSelection_Should_Wrap()
         {