Combobox select item only by mouse or Enter key

Question

I have a WPF ComboBox
I need to change default behaivor in popup list.

Now, by pressing up and down keys SelectedItem changes automatically.
I need change SelectedItem only by pressing Enter key, or clicking by mouse.

How can it be done?

I've subclassed ComboBox:

protected override void OnPreviewKeyDown(System.Windows.Input.KeyEventArgs e)
{
    Debug.Write("Pressed " + e.Key+ " ");
    if (e.Key == System.Windows.Input.Key.Up || e.Key == System.Windows.Input.Key.Down)
    {
        // ???
        e.Handled = true;
        return;
    }
    base.OnPreviewKeyDown(e);
}

This code doesn't work - no popup is shown and user can't select items. What I shoud write and where? :)

Thanks.

UPD1:

I need same functionality as ComboBox's popup is open and user can select items by mouse.
Each item can be hovered by mouse, but not selected. Selection become only by pressing mouse button. I need the same. 'Up' and 'Down' only highlights items in popup, but SelectedItem will be changed only by pressing Enter or mouse clicking.

UPD2: If I press by mouse on button, that opens Popup in ComboCox, I can highlight items in Popup by mouse, but SelectedItem will change only if I click on item.

I need same functionality by keyboard. If I start typing somewhat in ComboBox, Popup opens. And I have to hightlight items by keyboard Up and Down. TextBox in ComboBox must not change during highlighting and SelectedItem must change only if I press Enter (or mouse click)

UPD3: Link to demo solution: download

Answer 1

You should have this event handled on all the ComboBoxItems in a combobox.

   <ComboBox.Resources>
        <Style TargetType="{x:Type ComboBoxItem}">
           <EventSetter Event="PreviewKeyDown" Handler="OnPreviewKeyDown" />
        </Style> 
  </ComboBox.Resources>

EDIT:

In code behind, you can add folowing code in MyComboBox's constructor after InitializeComponent() do this...

  var comboBoxItemstyle = new Style(typeof (ComboBoxItem));  
  comboBoxItemstyle.Setters.Add(
        new EventSetter(PreviewKeyDownEvent,
                new KeyEventHandler(OnPreviewKeyDown)));
  this.Resources.Add(typeof (ComboBoxItem), comboBoxItemstyle);

Hope this helps.

Answer 2

The code you have seems to work fine, just add a check to see if the DropDown is open before cancelling the Key Event

protected override void OnPreviewKeyDown(KeyEventArgs e)
{
    Debug.Write("Pressed " + e.Key + " ");
    if (!base.IsDropDownOpen && (e.Key == Key.Up || e.Key == Key.Down))
    {
        e.Handled = true;
        return;
    }
    base.OnPreviewKeyDown(e);
}