void OnPreviewKeyDown(object sender, System.Windows.Input.KeyEventArgs e)
{
if (e.Key == Key.Back)
{
AssociatedObject.EditValue = null;
}
else if (e.Key >= Key.A && e.Key < Key.Z)
{
AssociatedObject.EditValue = HotKeyHelper.GetString(e.Key, e.KeyboardDevice.Modifiers);
}
e.Handled = true;
}
