Merge pull request #303 from AvaloniaUI/fixes/drag-drop-not-updating

Handle focused item being removed when outside the viewport.

Author: grokys

samples/TreeDataGridDemo/App.axaml.cs

@@ -9,6 +9,7 @@ public class App : Application
         public override void Initialize()
         {
             AvaloniaXamlLoader.Load(this);
+            Bogus.Randomizer.Seed = new System.Random(0);
         }
 
         public override void OnFrameworkInitializationCompleted()

src/Avalonia.Controls.TreeDataGrid/Primitives/TreeDataGridPresenterBase.cs

@@ -663,6 +663,13 @@ private void RecycleElement(Control element, int index)
 
         private void RecycleElementOnItemRemoved(Control element)
         {
+            if (element == _focusedElement)
+            {
+                _focusedElement.LostFocus -= OnUnrealizedFocusedElementLostFocus;
+                _focusedElement = null;
+                _focusedIndex = -1;
+            }
+
             UnrealizeElementOnItemRemoved(element);
             element.IsVisible = false;
             ElementFactory!.RecycleElement(element);
@@ -691,6 +698,12 @@ private void TrimUnrealizedChildren()
 
         private void OnItemsCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
+            void ClearFocusedElement(int index, int count)
+            {
+                if (_focusedElement is not null && _focusedIndex >= index && _focusedIndex < index + count)
+                    RecycleElementOnItemRemoved(_focusedElement);
+            }
+
             InvalidateMeasure();
 
             if (_realizedElements is null)
@@ -703,16 +716,21 @@ private void OnItemsCollectionChanged(object? sender, NotifyCollectionChangedEve
                     break;
                 case NotifyCollectionChangedAction.Remove:
                     _realizedElements.ItemsRemoved(e.OldStartingIndex, e.OldItems!.Count, _updateElementIndex, _recycleElementOnItemRemoved);
+                    ClearFocusedElement(e.OldStartingIndex, e.OldItems!.Count);
                     break;
                 case NotifyCollectionChangedAction.Replace:
                     _realizedElements.ItemsReplaced(e.OldStartingIndex, e.OldItems!.Count, _recycleElementOnItemRemoved);
+                    ClearFocusedElement(e.OldStartingIndex, e.OldItems!.Count);
                     break;
                 case NotifyCollectionChangedAction.Move:
                     _realizedElements.ItemsRemoved(e.OldStartingIndex, e.OldItems!.Count, _updateElementIndex, _recycleElementOnItemRemoved);
                     _realizedElements.ItemsInserted(e.NewStartingIndex, e.NewItems!.Count, _updateElementIndex);
+                    ClearFocusedElement(e.OldStartingIndex, e.OldItems!.Count);
                     break;
                 case NotifyCollectionChangedAction.Reset:
                     _realizedElements.ItemsReset(_recycleElementOnItemRemoved);
+                    if (_focusedElement is not null )
+                        RecycleElementOnItemRemoved(_focusedElement);
                     break;
             }
         }

tests/Avalonia.Controls.TreeDataGrid.Tests/Primitives/TreeDataGridRowsPresenterTests.cs

@@ -352,6 +352,78 @@ public void Handles_Removing_Row_Range_That_Invalidates_Current_Viewport()
             Assert.Equal(new Size(100, 100), target.Bounds.Size);
         }
 
+        [AvaloniaFact(Timeout = 10000)]
+        public void Handles_Removing_Focused_Row_While_Outside_Viewport()
+        {
+            var (target, scroll, items) = CreateTarget();
+            var element = target.RealizedElements.ElementAt(0)!;
+
+            element.Focusable = true;
+            element.Focus();
+
+            // Scroll down one item.
+            scroll.Offset = new Vector(0, 10);
+            Layout(target);
+
+            // Remove the focused element.
+            items.RemoveAt(0);
+
+            // Scroll back to the beginning.
+            scroll.Offset = new Vector(0, 0);
+            Layout(target);
+
+            // The correct element should be shown.
+            Assert.Same(items[0], target.RealizedElements.ElementAt(0)!.DataContext);
+        }
+
+        [AvaloniaFact(Timeout = 10000)]
+        public void Handles_Replacing_Focused_Row_While_Outside_Viewport()
+        {
+            var (target, scroll, items) = CreateTarget();
+            var element = target.RealizedElements.ElementAt(0)!;
+
+            element.Focusable = true;
+            element.Focus();
+
+            // Scroll down one item.
+            scroll.Offset = new Vector(0, 10);
+            Layout(target);
+
+            // Replace the focused element.
+            items[0] = new Model { Id = 100, Title = "New Item" };
+
+            // Scroll back to the beginning.
+            scroll.Offset = new Vector(0, 0);
+            Layout(target);
+
+            // The correct element should be shown.
+            Assert.Same(items[0], target.RealizedElements.ElementAt(0)!.DataContext);
+        }
+
+        [AvaloniaFact(Timeout = 10000)]
+        public void Handles_Moving_Focused_Row_While_Outside_Viewport()
+        {
+            var (target, scroll, items) = CreateTarget();
+            var element = target.RealizedElements.ElementAt(0)!;
+
+            element.Focusable = true;
+            element.Focus();
+
+            // Scroll down one item.
+            scroll.Offset = new Vector(0, 10);
+            Layout(target);
+
+            // Move the focused element.
+            items.Move(0, items.Count - 1);
+
+            // Scroll back to the beginning.
+            scroll.Offset = new Vector(0, 0);
+            Layout(target);
+
+            // The correct element should be shown.
+            Assert.Same(items[0], target.RealizedElements.ElementAt(0)!.DataContext);
+        }
+
         [AvaloniaFact(Timeout = 10000)]
         public void Updates_Star_Column_ActualWidth()
         {