New Post: CheckListBox : SelectedValue not updated on SelectedItems.Add/Remove

<StackPanel>
        <xctk:CheckListBox x:Name="_checkListBox"/>
       <TextBlock Text="{Binding SelectedValue, ElementName=_checkListBox}"/>
       <Button Content="ADD" Click="Button_Click"/>
    </StackPanel>

 public MainWindow()
    {
      InitializeComponent();

      _checkListBox.ItemsSource = new ObservableCollection<string>()
      {
         "Price",
        "Subban",
        "Galchenyuk",
      };
    }

    private void Button_Click( object sender, RoutedEventArgs e )
    {
      _checkListBox.SelectedItems.Add( "Subban" );
    }