Question

I have created a TreeViewComboBox control, in this I am having a ComboBox with items as TreeView, but Keyboard Navigation doesn’t work on the TreeView. I am not able to navigate through the TreeViewItems using keyboard. Any help plz?

Answer 1

I has a similar issue when implementing our property grid control. The issue in our specific, which could be similar to yours, was that the keyboard focus events were not routing to the TreeViewItem.

The way we solved it was by adding an AttachedProperty to the TreeViewItem style and selecting the node when it gets keyboard focus. I implemented this using a Service pattern. See below:

In XAML:

<Style x:Key="EditorBorder" TargetType="{x:Type Border}">
    <Setter Property="Controls_Services:TreeViewItemService.SelectWhenKeyboardIsFocused" Value="True"/>
</Style>

In Codebehind:

  public class TreeViewItemService
  {
    public static readonly DependencyProperty SelectWhenKeyboardIsFocusedProperty = DependencyProperty.RegisterAttached("SelectWhenKeyboardIsFocused",
      typeof(bool), typeof(TreeViewItemService), new FrameworkPropertyMetadata(false, TreeViewItemService.OnSelectWhenKeyboardIsFocusedPropertyChanged));

    static void OnSelectWhenKeyboardIsFocusedPropertyChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
      FrameworkElement element = sender as FrameworkElement;
      if (element == null)
        return;

      TreeViewItem target = MTVisualTreeHelper.FindParent<TreeViewItem>(element as DependencyObject);
      if (target != null)
        new IsSelectedOnKeyboardFocusAction(element, target);
    }

    public static bool GetSelectWhenKeyboardIsFocused(FrameworkElement target)
    {
      return (bool)target.GetValue(SelectWhenKeyboardIsFocusedProperty);
    }

    public static void SetSelectWhenKeyboardIsFocused(FrameworkElement target, bool value)
    {
      target.SetValue(SelectWhenKeyboardIsFocusedProperty, value);
    }

    private class IsSelectedOnKeyboardFocusAction
    {
      TreeViewItem m_Target;
      FrameworkElement m_Source;

      public IsSelectedOnKeyboardFocusAction(FrameworkElement source, TreeViewItem item)
      {
        m_Source = source;
        m_Target = item;
        m_Source.Loaded += OnSource_Loaded;
        m_Source.Unloaded += OnSource_Unloaded;
      }

      void OnSource_Loaded(object sender, RoutedEventArgs e)
      {
        m_Source.PreviewMouseLeftButtonDown += OnSource_PreviewMouseLeftButtonDown;
        m_Source.GotFocus += OnSource_GotFocus;
        m_Source.LostFocus += OnSource_LostFocus;
        m_Source.GotKeyboardFocus += OnSource_GotKeyboardFocus;
        m_Source.LostKeyboardFocus += OnSource_LostKeyboardFocus;
      }

      void OnSource_Unloaded(object sender, RoutedEventArgs e)
      {
        m_Source.PreviewMouseLeftButtonDown -= OnSource_PreviewMouseLeftButtonDown;
        m_Source.GotFocus -= OnSource_GotFocus;
        m_Source.LostFocus -= OnSource_LostFocus;
        m_Source.GotKeyboardFocus -= OnSource_GotKeyboardFocus;
        m_Source.LostKeyboardFocus -= OnSource_LostKeyboardFocus;
      }

      void OnSource_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
      {
        if (!m_Target.IsSelected)
          m_Target.IsSelected = true;
      }

      void OnSource_GotFocus(object sender, RoutedEventArgs e)
      {
        if (!m_Target.IsSelected)
          m_Target.IsSelected = true;
      }

      void OnSource_LostFocus(object sender, RoutedEventArgs e)
      {
        if (m_Target.IsSelected)
          m_Target.IsSelected = false;
      }

      void OnSource_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
      {
        if (!m_Target.IsSelected)
          m_Target.IsSelected = true;
      }

      void OnSource_LostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
      {
        if (m_Target.IsSelected)
          m_Target.IsSelected = false;
      }

    }

  }

HTH,