Merge pull request #5817 from AvaloniaUI/fixes/selecteditems-binding

Don't update SelectedItems when setting items source.

src/Avalonia.Controls/Selection/InternalSelectionModel.cs

@@ -80,10 +80,12 @@ namespace Avalonia.Controls.Selection
             try
             {
                 _ignoreSelectedItemsChanges = true;
+                ++_ignoreModelChanges;
                 base.SetSource(value);
             }
             finally
             {
+                --_ignoreModelChanges;
                 _ignoreSelectedItemsChanges = false;
             }
 
@@ -93,17 +95,14 @@ namespace Avalonia.Controls.Selection
             }
             else
             {
-                foreach (var i in oldSelection)
-                {
-                    var index = ItemsView!.IndexOf(i);
-                    Select(index);
-                }
+                SyncFromSelectedItems();
             }
         }
 
         private void SyncToSelectedItems()
         {
-            if (_writableSelectedItems is object)
+            if (_writableSelectedItems is object &&
+                !SequenceEqual(_writableSelectedItems, base.SelectedItems))
             {
                 try
                 {
@@ -224,6 +223,7 @@ namespace Avalonia.Controls.Selection
             if (_isResetting)
             {
                 --_ignoreModelChanges;
+                _isResetting = false;
             }
         }
 
@@ -310,5 +310,27 @@ namespace Avalonia.Controls.Selection
 
             return -1;
         }
+
+        private static bool SequenceEqual(IList first, IReadOnlyList<object?> second)
+        {
+            if (first is IEnumerable<object?> e)
+            {
+                return e.SequenceEqual(second);
+            }
+
+            var comparer = EqualityComparer<object?>.Default;
+            var e1 = first.GetEnumerator();
+            using var e2 = second.GetEnumerator();
+
+            while (e1.MoveNext())
+            {
+                if (!(e2.MoveNext() && comparer.Equals(e1.Current, e2.Current)))
+                {
+                    return false;
+                }
+            }
+
+            return !e2.MoveNext();
+        }
     }
 }

tests/Avalonia.Controls.UnitTests/ListBoxTests.cs

@@ -1,3 +1,4 @@
+using System.Collections.ObjectModel;
 using System.Linq;
 using System.Reactive.Subjects;
 using Avalonia.Collections;
@@ -457,6 +458,33 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Initial_Binding_Of_SelectedItems_Should_Not_Cause_Write_To_SelectedItems()
+        {
+            var target = new ListBox
+            {
+                [!ListBox.ItemsProperty] = new Binding("Items"),
+                [!ListBox.SelectedItemsProperty] = new Binding("SelectedItems"),
+            };
+
+            var viewModel = new
+            {
+                Items = new[] { "Foo", "Bar", "Baz " },
+                SelectedItems = new ObservableCollection<string> { "Bar" },
+            };
+
+            var raised = 0;
+
+            viewModel.SelectedItems.CollectionChanged += (s, e) => ++raised;
+
+            target.DataContext = viewModel;
+
+            Assert.Equal(0, raised);
+            Assert.Equal(new[] { "Bar" }, viewModel.SelectedItems);
+            Assert.Equal(new[] { "Bar" }, target.SelectedItems);
+            Assert.Equal(new[] { "Bar" }, target.Selection.SelectedItems);
+        }
+
         private FuncControlTemplate ListBoxTemplate()
         {
             return new FuncControlTemplate<ListBox>((parent, scope) =>