public void RegisterListener(GameEventMultipleListener listener, int index)
 {
     if (eventListeners.Find(ltn => ltn.listener == listener) == null)
     {
         eventListeners.Add(new ElementListener(listener, index));
     }
 }
 public ElementListener(GameEventMultipleListener listener, int index)
 {
     this.listener = listener;
     this.index    = index;
 }
 public void UnregisterListener(GameEventMultipleListener listener, int index)
 {
     var count = eventListeners.RemoveAll(lmt => lmt.listener == listener && lmt.index == index);
 }