Scroll and focus to selected item when dropdown is shown

src/Avalonia.Controls/DropDown.cs

@@ -190,6 +190,14 @@ namespace Avalonia.Controls
             base.OnTemplateApplied(e);
         }
 
+        internal void ItemFocused(DropDownItem dropDownItem)
+        {
+            if (IsDropDownOpen && dropDownItem.IsFocused && dropDownItem.IsArrangeValid)
+            {
+                dropDownItem.BringIntoView();
+            }
+        }
+
         private void PopupClosed(object sender, EventArgs e)
         {
             if (Focusable)

src/Avalonia.Controls/DropDownItem.cs

@@ -2,43 +2,19 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System;
+using System.Reactive.Linq;
 
 namespace Avalonia.Controls
 {
     /// <summary>
     /// A selectable item in a <see cref="DropDown"/>.
     /// </summary>
-    public class DropDownItem : ContentControl, ISelectable
+    public class DropDownItem : ListBoxItem
     {
-        /// <summary>
-        /// Defines the <see cref="IsSelected"/> property.
-        /// </summary>
-        public static readonly StyledProperty<bool> IsSelectedProperty =
-            AvaloniaProperty.Register<DropDownItem, bool>(nameof(IsSelected));
-
-        /// <summary>
-        /// Initializes static members of the <see cref="DropDownItem"/> class.
-        /// </summary>
-        static DropDownItem()
-        {
-            FocusableProperty.OverrideDefaultValue<DropDownItem>(true);
-        }
-
         public DropDownItem()
         {
-            this.GetObservable(DropDownItem.IsFocusedProperty).Subscribe(focused =>
-            {
-                PseudoClasses.Set(":selected", focused);                
-            });
-        }
-
-        /// <summary>
-        /// Gets or sets the selection state of the item.
-        /// </summary>
-        public bool IsSelected
-        {
-            get { return GetValue(IsSelectedProperty); }
-            set { SetValue(IsSelectedProperty, value); }
+            this.GetObservable(DropDownItem.IsFocusedProperty).Where(focused => focused)
+                .Subscribe(_ => (Parent as DropDown)?.ItemFocused(this));
         }
     }
 }