/// <summary>
 /// 删除一个消息接收器
 /// </summary>
 /// <param name="listener">要删除的消息接收器</param>
 /// <returns></returns>
 public static bool Remove(Listener listener)
 {
     lock (NeedRemoveListeners)
     {
         if (!Contains(listener)) return false;
         NeedRemoveListeners.Add(listener);
         return true;
     }
 }
 /// <summary>
 /// 添加一个消息接收器
 /// </summary>
 /// <param name="listener">要添加的消息接收器</param>
 /// <returns></returns>
 public static bool Add(Listener listener)
 {
     lock (NeedAddListeners)
     {
         if (Contains(listener)) return false;
         NeedAddListeners.Add(listener);
         return true;
     }
 }
 /// <summary>
 /// 确定指定的消息接收器是否已经被添加
 /// </summary>
 /// <param name="listener">目标消息接收器</param>
 /// <returns></returns>
 public static bool Contains(Listener listener)
 {
     lock (NeedRemoveListeners)
     {
         lock (NeedAddListeners)
         {
             lock (Listeners)
             {
                 return Listeners.Contains(listener) || NeedAddListeners.Contains(listener) || NeedRemoveListeners.Contains(listener);
             }
         }
     }
 }