feat: working on selection. add a demo to AutoCompleteBoxDemo to show the keyboard navigation actually changed selection.

demo/Ursa.Demo/Pages/AutoCompleteBoxDemo.axaml

@@ -23,10 +23,14 @@
             </Style>
         </StackPanel.Styles>
 
+        <TextBlock Text="{Binding #box.((viewModels:StateData)SelectedItem).Name}" />
+        
         <u:AutoCompleteBox
+            Name="box"
             Watermark="Please select a State"
             Classes="ClearButton"
             ValueMemberBinding="{ReflectionBinding Name}" />
+        
         <u:AutoCompleteBox
             Classes="Large"
             ValueMemberBinding="{ReflectionBinding Name}" />

demo/Ursa.Demo/Pages/MultiAutoCompleteBoxDemo.axaml

@@ -10,6 +10,7 @@
     <StackPanel Spacing="20">
         <TextBlock Text="Multi-AutoCompleteBox"/>
         <u:MultiAutoCompleteBox ItemsSource="{Binding Items}" 
+                                SelectedItems="{Binding SelectedItems}"
                                 ItemFilter="{Binding FilterPredicate }"
                                 FilterMode="Custom">
             <u:MultiAutoCompleteBox.ItemTemplate>
@@ -22,6 +23,11 @@
                     </TextBlock>
                 </DataTemplate>
             </u:MultiAutoCompleteBox.ItemTemplate>
+            <u:MultiAutoCompleteBox.SelectedItemTemplate>
+                <DataTemplate DataType="vm:ControlData">
+                    <TextBlock Text="{Binding MenuHeader}" />
+                </DataTemplate>
+            </u:MultiAutoCompleteBox.SelectedItemTemplate>
         </u:MultiAutoCompleteBox>
     </StackPanel>
 </UserControl>

demo/Ursa.Demo/ViewModels/MultiAutoCompleteBoxDemoViewModel.cs

@@ -8,10 +8,12 @@ namespace Ursa.Demo.ViewModels;
 public class MultiAutoCompleteBoxDemoViewModel: ObservableObject
 {
     public ObservableCollection<ControlData> Items { get; set; }
+    public ObservableCollection<ControlData> SelectedItems { get; set; }
     public AutoCompleteFilterPredicate<object> FilterPredicate { get; set; }
 
     public MultiAutoCompleteBoxDemoViewModel()
     {
+        SelectedItems = new ObservableCollection<ControlData>();
         Items = new ObservableCollection<ControlData>
         {
             new() { MenuHeader = "Button Group", Chinese = "按钮组" },