//接收和发送信息
        private void ReceiveData()
        {
            bool keepalive = true;
            TcpClient s = clientTcp;
            NetworkStream ns = s.GetStream();   //可以获取网络流对象，以此来发送和接收信息
            byte[] buffer = new byte[s.Available];
            
            //根据收到的客户端套接字向客户端发送消息
            //IPEndPoint clientiep = (IPEndPoint)s.Client.RemoteEndPoint;   //获取远程终结点
            //string welcome = "已收到！";
            //byte[] data = new byte[1024];
            //data = Encoding.ASCII.GetBytes(welcome);
            //ns.Write(data, 0, data.Length);


            screenStr = "";  //暂存一次截屏的内容

            while(keepalive)
            {
                //在套接字上接收客户端发送的消息
                int bufLen = 0;
                try
                {
                    bufLen = s.Available;
                    ns.Read(buffer, 0, bufLen); //来到这里出错：超出有效值范围size
                    screenStr += Encoding.ASCII.GetString(buffer);

                    if (bufLen == 0)
                        continue;
                }
                catch(Exception ex)
                {
                    MessageBox.Show("server Receive Error：" + ex.Message);
                    return;
                }
            }
            //接收完处理显示截屏
            //screenByte = Encoding.ASCII.GetBytes(screenStr);
            showImg simg = new showImg(showScreen);
            isInvoke(simg);
        }