Make ScrollIntoView accept an index, not an item.

Fixes #2569.

src/Avalonia.Controls/ComboBox.cs

@@ -291,7 +291,7 @@ namespace Avalonia.Controls
 
                 if (container == null && SelectedIndex != -1)
                 {
-                    ScrollIntoView(Selection.SelectedItem);
+                    ScrollIntoView(Selection.SelectedIndex);
                     container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);
                 }
 

src/Avalonia.Controls/Presenters/IItemsPresenter.cs

@@ -14,6 +14,6 @@ namespace Avalonia.Controls.Presenters
 
         void ItemsChanged(NotifyCollectionChangedEventArgs e);
 
-        void ScrollIntoView(object item);
+        void ScrollIntoView(int index);
     }
 }

src/Avalonia.Controls/Presenters/ItemVirtualizer.cs

@@ -257,8 +257,8 @@ namespace Avalonia.Controls.Presenters
         /// <summary>
         /// Scrolls the specified item into view.
         /// </summary>
-        /// <param name="item">The item.</param>
-        public virtual void ScrollIntoView(object item)
+        /// <param name="index">The index of the item.</param>
+        public virtual void ScrollIntoView(int index)
         {
         }
 

src/Avalonia.Controls/Presenters/ItemVirtualizerNone.cs

@@ -67,18 +67,13 @@ namespace Avalonia.Controls.Presenters
         /// <summary>
         /// Scrolls the specified item into view.
         /// </summary>
-        /// <param name="item">The item.</param>
-        public override void ScrollIntoView(object item)
+        /// <param name="index">The index of the item.</param>
+        public override void ScrollIntoView(int index)
         {
-            if (Items != null)
+            if (index != -1)
             {
-                var index = Items.IndexOf(item);
-
-                if (index != -1)
-                {
-                    var container = Owner.ItemContainerGenerator.ContainerFromIndex(index);
-                    container?.BringIntoView();
-                }
+                var container = Owner.ItemContainerGenerator.ContainerFromIndex(index);
+                container?.BringIntoView();
             }
         }
 

src/Avalonia.Controls/Presenters/ItemVirtualizerSimple.cs

@@ -289,20 +289,15 @@ namespace Avalonia.Controls.Presenters
                     break;
             }
 
-            return ScrollIntoView(newItemIndex);
+            return ScrollIntoViewCore(newItemIndex);
         }
 
         /// <inheritdoc/>
-        public override void ScrollIntoView(object item)
+        public override void ScrollIntoView(int index)
         {
-            if (Items != null)
+            if (index != -1)
             {
-                var index = Items.IndexOf(item);
-
-                if (index != -1)
-                {
-                    ScrollIntoView(index);
-                }
+                ScrollIntoViewCore(index);
             }
         }
 
@@ -514,7 +509,7 @@ namespace Avalonia.Controls.Presenters
         /// </summary>
         /// <param name="index">The item index.</param>
         /// <returns>The container that was brought into view.</returns>
-        private IControl ScrollIntoView(int index)
+        private IControl ScrollIntoViewCore(int index)
         {
             var panel = VirtualizingPanel;
             var generator = Owner.ItemContainerGenerator;

src/Avalonia.Controls/Presenters/ItemsPresenter.cs

@@ -120,9 +120,9 @@ namespace Avalonia.Controls.Presenters
             return Virtualizer?.GetControlInDirection(direction, from);
         }
 
-        public override void ScrollIntoView(object item)
+        public override void ScrollIntoView(int index)
         {
-            Virtualizer?.ScrollIntoView(item);
+            Virtualizer?.ScrollIntoView(index);
         }
 
         /// <inheritdoc/>

src/Avalonia.Controls/Presenters/ItemsPresenterBase.cs

@@ -142,7 +142,7 @@ namespace Avalonia.Controls.Presenters
         }
 
         /// <inheritdoc/>
-        public virtual void ScrollIntoView(object item)
+        public virtual void ScrollIntoView(int index)
         {
         }
 

src/Avalonia.Controls/Primitives/SelectingItemsControl.cs

@@ -339,11 +339,17 @@ namespace Avalonia.Controls.Primitives
             base.EndInit();
         }
 
+        /// <summary>
+        /// Scrolls the specified item into view.
+        /// </summary>
+        /// <param name="index">The index of the item.</param>
+        public void ScrollIntoView(int index) => Presenter?.ScrollIntoView(index);
+
         /// <summary>
         /// Scrolls the specified item into view.
         /// </summary>
         /// <param name="item">The item.</param>
-        public void ScrollIntoView(object item) => Presenter?.ScrollIntoView(item);
+        public void ScrollIntoView(object item) => ScrollIntoView(IndexOf(Items, item));
 
         /// <summary>
         /// Tries to get the container that was the source of an event.
@@ -665,12 +671,9 @@ namespace Avalonia.Controls.Primitives
         {
             if (e.PropertyName == nameof(SelectionModel.AnchorIndex) && AutoScrollToSelectedItem)
             {
-                var index = Selection.AnchorIndex.GetSize() > 0 ? Selection.AnchorIndex.GetAt(0) : -1;
-                var item = index != -1 ? ElementAt(Items, index) : null;
-
-                if (item != null)
+                if (Selection.AnchorIndex.GetSize() > 0)
                 {
-                    ScrollIntoView(item);
+                    ScrollIntoView(Selection.AnchorIndex.GetAt(0));
                 }
             }
         }

src/Avalonia.Dialogs/ManagedFileChooser.xaml.cs

@@ -81,7 +81,7 @@ namespace Avalonia.Dialogs
 
             if (indexOfPreselected > 1)
             {
-                _filesView.ScrollIntoView(model.Items[indexOfPreselected - 1]);
+                _filesView.ScrollIntoView(indexOfPreselected - 1);
             }
         }
     }

tests/Avalonia.Controls.UnitTests/Presenters/ItemsPresenterTests_Virtualization_Simple.cs

@@ -575,7 +575,7 @@ namespace Avalonia.Controls.UnitTests.Presenters
                 target.Arrange(Rect.Empty);
 
                 // Check for issue #591: this should not throw.
-                target.ScrollIntoView(items[0]);
+                target.ScrollIntoView(0);
             }
         }
 
@@ -729,7 +729,7 @@ namespace Avalonia.Controls.UnitTests.Presenters
 
             var last = (target.Items as IList)[10];
 
-            target.ScrollIntoView(last);
+            target.ScrollIntoView(10);
 
             Assert.Equal(new Vector(0, 1), ((ILogicalScrollable)target).Offset);
             Assert.Same(target.Panel.Children[9].DataContext, last);
@@ -746,12 +746,12 @@ namespace Avalonia.Controls.UnitTests.Presenters
 
             var last = (target.Items as IList)[10];
 
-            target.ScrollIntoView(last);
+            target.ScrollIntoView(10);
 
             Assert.Equal(new Vector(0, 1), ((ILogicalScrollable)target).Offset);
             Assert.Same(target.Panel.Children[9].DataContext, last);
 
-            target.ScrollIntoView(last);
+            target.ScrollIntoView(10);
 
             Assert.Equal(new Vector(0, 1), ((ILogicalScrollable)target).Offset);
             Assert.Same(target.Panel.Children[9].DataContext, last);