Merge pull request #10759 from AvaloniaUI/fixes/treeview-selecteditem-inside-selectionchanged-event

Fix TreeView SelectedItem sync

src/Avalonia.Controls/TreeView.cs

@@ -307,12 +307,14 @@ namespace Avalonia.Controls
 
         private void SelectSingleItem(object item)
         {
+            var oldValue = _selectedItem;
             _syncingSelectedItems = true;
-            SelectedItems.Clear();            
+            SelectedItems.Clear();
+            _selectedItem = item;
             SelectedItems.Add(item);
             _syncingSelectedItems = false;
 
-            SetAndRaise(SelectedItemProperty, ref _selectedItem, item);            
+            RaisePropertyChanged(SelectedItemProperty, oldValue, _selectedItem);    
         }
 
         /// <summary>

tests/Avalonia.Controls.UnitTests/TreeViewTests.cs

@@ -722,6 +722,33 @@ namespace Avalonia.Controls.UnitTests
             Assert.True(called);
         }
 
+        [Fact]
+        public void SelectedItem_Should_Be_Valid_When_SelectedItemChanged_Event_Raised()
+        {
+            using var app = Start();
+            var data = CreateTestTreeData();
+            var target = CreateTarget(data: data);
+
+            var item = data[0].Children[1].Children[0];
+            var container = Assert.IsType<TreeViewItem>(target.TreeContainerFromItem(item));
+
+            Assert.NotNull(container);
+
+            var called = false;
+            target.SelectionChanged += (s, e) =>
+            {
+                Assert.Same(item, e.AddedItems[0]);
+                Assert.Same(item, target.SelectedItem);
+                called = true;
+            };
+
+            _mouse.Click(container);
+
+            Assert.Equal(item, target.SelectedItem);
+            Assert.True(container.IsSelected);
+            Assert.True(called);
+        }
+
         [Fact]
         public void Bound_SelectedItem_Should_Not_Be_Cleared_when_Changing_Selection()
         {
@@ -756,7 +783,7 @@ namespace Avalonia.Controls.UnitTests
             using var app = Start();
             var data = CreateTestTreeData();
             var target = CreateTarget(data: data, expandAll: false);
-            
+
             target.SelectedItem = data[0].Children[1];
 
             var rootItem = Assert.IsType<TreeViewItem>(target.ContainerFromIndex(0));