ComboBox PreviewKeyDown doesn't fire for Return key

Question

I'm want to conditionally prevent the Enter/Return key from selecting the highlighted item in a ComboBox drop down. So I wired up an event handler to the ComboBox.PreviewKeyDown so that I could set the Handled property, but the event handler is never entered. When I use Snoop to watch the events, the PreviewKeyDown event is fired for other keys but it never fires when I press the return key; not even at the Window level. Why isn't the event firing?

EDIT: The ComboBox needs to be editable (IsEditable=true). Then open the drop down list. Begin typing in an item in your list and it should select it for you. Press the return key.

Answer 1

That's because WPF internally handles the event when the drop-down is open and enter key is pressed. That's the default WPF behavior.

To solve, extend the ComboBox and override the OnPreviewKeyDown method.

public class MyComboBox : ComboBox
{
    protected override void OnPreviewKeyDown(KeyEventArgs e)
    {
        bool isDropDownOpen = IsDropDownOpen;

        base.OnPreviewKeyDown(e);

        if (isDropDownOpen)
        {
            e.Handled = false;
        }
    }
}