Use Adorner Focus styling for focused DropDownItem

src/Avalonia.Controls/DropDown.cs

@@ -165,10 +165,10 @@ namespace Avalonia.Controls
             else if (IsDropDownOpen && SelectedIndex < 0 && ItemCount > 0 &&
                       (e.Key == Key.Up || e.Key == Key.Down))
             {
-                var firstChild = Presenter?.Panel?.Children.FirstOrDefault(c => c.Focusable);
+                var firstChild = Presenter?.Panel?.Children.FirstOrDefault(c => CanFocus(c));
                 if (firstChild != null)
                 {
-                    firstChild.Focus();
+                    FocusManager.Instance?.Focus(firstChild, NavigationMethod.Directional);
                     e.Handled = true;
                 }
             }
@@ -223,7 +223,7 @@ namespace Avalonia.Controls
 
         private void PopupClosed(object sender, EventArgs e)
         {
-            if (Focusable)
+            if (CanFocus(this))
             {
                 Focus();
             }
@@ -246,13 +246,15 @@ namespace Avalonia.Controls
             if (IsDropDownOpen && selectedIndex != -1)
             {
                 var container = ItemContainerGenerator.ContainerFromIndex(selectedIndex);
-                if (container != null && container.Focusable)
+                if (container != null && CanFocus(container))
                 {
                     container.Focus();
                 }
             }
         }
 
+        private bool CanFocus(IControl control) => control.Focusable && control.IsEnabledCore && control.IsVisible;
+
         private void UpdateSelectionBoxItem(object item)
         {
             var contentControl = item as IContentControl;

src/Avalonia.Themes.Default/DropDown.xaml

@@ -39,15 +39,17 @@
                    StaysOpen="False">
               <Border BorderBrush="{DynamicResource ThemeBorderMidBrush}"
                       BorderThickness="1">
-                <ScrollViewer>
-                  <ItemsPresenter Name="PART_ItemsPresenter"
-                                  Items="{TemplateBinding Items}"
-                                  ItemsPanel="{TemplateBinding ItemsPanel}"
-                                  ItemTemplate="{TemplateBinding ItemTemplate}"
-                                  MemberSelector="{TemplateBinding MemberSelector}"
-                                  VirtualizationMode="{TemplateBinding VirtualizationMode}"
+                  <AdornerDecorator Margin="-1 -1 0 0">
+                      <ScrollViewer>
+                          <ItemsPresenter Name="PART_ItemsPresenter"
+                                          Items="{TemplateBinding Items}"
+                                          ItemsPanel="{TemplateBinding ItemsPanel}"
+                                          ItemTemplate="{TemplateBinding ItemTemplate}"
+                                          MemberSelector="{TemplateBinding MemberSelector}"
+                                          VirtualizationMode="{TemplateBinding VirtualizationMode}"
                                   />
-                </ScrollViewer>
+                      </ScrollViewer>
+                  </AdornerDecorator>
               </Border>
             </Popup>
           </Grid>
@@ -58,4 +60,4 @@
   <Style Selector="DropDown:pointerover /template/ Border#border">
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderHighBrush}"/>
   </Style>
-</Styles>
+</Styles>

src/Avalonia.Themes.Default/DropDownItem.xaml

@@ -4,7 +4,6 @@
     <Setter Property="Padding" Value="2"/>
     <Setter Property="HorizontalAlignment" Value="Stretch"/>
     <Setter Property="HorizontalContentAlignment" Value="Left"/>
-    <Setter Property="BorderThickness" Value="1"/>
     <Setter Property="Template">
       <ControlTemplate>
         <ContentPresenter Name="PART_ContentPresenter"
@@ -20,10 +19,6 @@
     </Setter>
   </Style>
     
-  <Style Selector="DropDownItem:focus /template/ ContentPresenter">
-      <Setter Property="BorderBrush" Value="{DynamicResource ThemeAccentBrush3}"/>
-  </Style>
-    
   <Style Selector="DropDownItem:pointerover /template/ ContentPresenter">
     <Setter Property="Background" Value="{DynamicResource ThemeControlHighlightMidBrush}"/>
   </Style>

src/Avalonia.Themes.Default/FocusAdorner.xaml

@@ -3,7 +3,8 @@
     <FocusAdornerTemplate>
       <Rectangle Stroke="Black"
                  StrokeThickness="1"
-                 StrokeDashArray="1,2"/>
+                 StrokeDashArray="1,2"
+                 Margin="1"/>
     </FocusAdornerTemplate>
   </Setter>
-</Style>
+</Style>