public void UnRegister(IBackEventReceiver receiver)
 {
     if (_receivers.Count <= 0)
     {
         return;
     }
     _receivers.Pop();
 }
        private void Notify()
        {
            IBackEventReceiver receiver = _receivers.Peek();

            receiver.ReceiveBackButton();
        }
 public void Register(IBackEventReceiver receiver)
 {
     _receivers.Push(receiver);
 }