// 启动服务器
    // 根据博客中协议的设计部分
    // 客户端先向服务器发送登录请求，然后通过服务器返回的端口号
    // 再与服务器建立连接
    // 所以启动服务按钮事件中有两个套接字：一个是接收客户端信息套接字和
    // 监听客户端连接套接字
    private void btnStart_Click(object sender, EventArgs e)
    {
      // 创建接收套接字
      serverIp = IPAddress.Parse(txbServerIP.Text);
      serverIPEndPoint = new IPEndPoint(serverIp, int.Parse(txbServerport.Text));
      receiveUdpClient = new UdpClient(serverIPEndPoint);
      // 启动接收线程
      Thread receiveThread = new Thread(ReceiveMessage);
      receiveThread.Start();
      btnStart.Enabled = false;
      btnStop.Enabled = true;

      // 随机指定监听端口
      Random random = new Random();
      tcpPort = random.Next(port + 1, 65536);

      // 创建监听套接字
      tcpListener = new TcpListener(serverIp, tcpPort);
      tcpListener.Start();

      // 启动监听线程
      Thread listenThread = new Thread(ListenClientConnect);
      listenThread.Start();
      AddItemToListBox(string.Format("服务器线程{0}启动，监听端口{1}",serverIPEndPoint,tcpPort));
    }

    // 接收客户端发来的信息
    private void ReceiveMessage()
    {
      IPEndPoint remoteIPEndPoint = new IPEndPoint(IPAddress.Any, 0);
      while (true)
      {
        try
        {
          // 关闭receiveUdpClient时下面一行代码会产生异常
          byte[] receiveBytes = receiveUdpClient.Receive(ref remoteIPEndPoint);
          string message = Encoding.Unicode.GetString(receiveBytes, 0, receiveBytes.Length);

          // 显示消息内容
          AddItemToListBox(string.Format("{0}:{1}",remoteIPEndPoint,message));

          // 处理消息数据
          // 根据协议的设计部分，从客户端发送来的消息是具有一定格式的
          // 服务器接收消息后要对消息做处理
          string[] splitstring = message.Split(',');
          // 解析用户端地址
          string[] splitsubstring = splitstring[2].Split(':');
          IPEndPoint clientIPEndPoint = new IPEndPoint(IPAddress.Parse(splitsubstring[0]), int.Parse(splitsubstring[1]));
          switch (splitstring[0])
          {
            // 如果是登录信息，向客户端发送应答消息和广播有新用户登录消息
            case "login":
              User user = new User(splitstring[1], clientIPEndPoint);
              // 往在线的用户列表添加新成员
              userList.Add(user);
              AddItemToListBox(string.Format("用户{0}({1})加入", user.GetName(), user.GetIPEndPoint()));
              string sendString = "Accept," + tcpPort.ToString();
              // 向客户端发送应答消息
              SendtoClient(user, sendString);
              AddItemToListBox(string.Format("向{0}({1})发出：[{2}]", user.GetName(), user.GetIPEndPoint(), sendString));
              for (int i = 0; i < userList.Count; i++)
              {
                if (userList[i].GetName() != user.GetName())
                {
                  // 给在线的其他用户发送广播消息
                  // 通知有新用户加入
                  SendtoClient(userList[i], message);
                }
              }

              AddItemToListBox(string.Format("广播：[{0}]", message));
              break;
            case "logout":
              for (int i = 0; i < userList.Count; i++)
              {
                if (userList[i].GetName() == splitstring[1])
                {
                  AddItemToListBox(string.Format("用户{0}({1})退出",userList[i].GetName(),userList[i].GetIPEndPoint()));
                  userList.RemoveAt(i); // 移除用户
                }
              }
              for (int i = 0; i < userList.Count; i++)
              {
                // 广播注销消息
                SendtoClient(userList[i], message);
              }
              AddItemToListBox(string.Format("广播:[{0}]", message));
              break;
          }
        }
        catch
        {
          // 发送异常退出循环
          break;
        }
      }
      AddItemToListBox(string.Format("服务线程{0}终止", serverIPEndPoint));
    }

    // 向客户端发送消息
    private void SendtoClient(User user, string message)
    {
      // 匿名方式发送
      sendUdpClient = new UdpClient(0);
      byte[] sendBytes = Encoding.Unicode.GetBytes(message);
      IPEndPoint remoteIPEndPoint =user.GetIPEndPoint();
      sendUdpClient.Send(sendBytes,sendBytes.Length,remoteIPEndPoint);
      sendUdpClient.Close();
    }
    
    // 接受客户端的连接
    private void ListenClientConnect()
    {
      TcpClient newClient = null;
      while (true)
      {
        try
        {
          newClient = tcpListener.AcceptTcpClient();
          AddItemToListBox(string.Format("接受客户端{0}的TCP请求",newClient.Client.RemoteEndPoint));
        }
        catch
        {
          AddItemToListBox(string.Format("监听线程({0}:{1})", serverIp, tcpPort));
          break;
        }

        Thread sendThread = new Thread(SendData);
        sendThread.Start(newClient);
      }
    }

    // 向客户端发送在线用户列表信息
    // 服务器通过TCP连接把在线用户列表信息发送给客户端
    private void SendData(object userClient)
    {
      TcpClient newUserClient = (TcpClient)userClient;
      userListstring = null;
      for (int i = 0; i < userList.Count; i++)
      {
        userListstring += userList[i].GetName() + ","
          + userList[i].GetIPEndPoint().ToString() + ";";
      }

      userListstring += "end";
      networkStream = newUserClient.GetStream();
      binaryWriter = new BinaryWriter(networkStream);
      binaryWriter.Write(userListstring);
      binaryWriter.Flush();
      AddItemToListBox(string.Format("向{0}发送[{1}]", newUserClient.Client.RemoteEndPoint, userListstring));
      binaryWriter.Close();
      newUserClient.Close();
    }

// 登录服务器
    private void btnlogin_Click(object sender, EventArgs e)
    {
      // 创建接受套接字
      IPAddress clientIP = IPAddress.Parse(txtLocalIP.Text);
      clientIPEndPoint = new IPEndPoint(clientIP, int.Parse(txtlocalport.Text));
      receiveUdpClient = new UdpClient(clientIPEndPoint);
      // 启动接收线程
      Thread receiveThread = new Thread(ReceiveMessage);
      receiveThread.Start();

      // 匿名发送
      sendUdpClient = new UdpClient(0);
      // 启动发送线程
      Thread sendThread = new Thread(SendMessage);
      sendThread.Start(string.Format("login,{0},{1}", txtusername.Text, clientIPEndPoint));

      btnlogin.Enabled = false;
      btnLogout.Enabled = true;
      this.Text = txtusername.Text;
    }

    // 客户端接受服务器回应消息 
    private void ReceiveMessage()
    {
      IPEndPoint remoteIPEndPoint = new IPEndPoint(IPAddress.Any,0);
      while (true)
      {
        try
        {
          // 关闭receiveUdpClient时会产生异常
          byte[] receiveBytes = receiveUdpClient.Receive(ref remoteIPEndPoint);
          string message = Encoding.Unicode.GetString(receiveBytes,0,receiveBytes.Length);

          // 处理消息
          string[] splitstring = message.Split(',');

          switch (splitstring[0])
          {
            case "Accept":
              try
              {
                tcpClient = new TcpClient();
                tcpClient.Connect(remoteIPEndPoint.Address, int.Parse(splitstring[1]));
                if (tcpClient != null)
                {
                  // 表示连接成功
                  networkStream = tcpClient.GetStream();
                  binaryReader = new BinaryReader(networkStream);
                }
              }
              catch
              {
                MessageBox.Show("连接失败", "异常");
              }

              Thread getUserListThread = new Thread(GetUserList);
              getUserListThread.Start();
              break;
            case "login":
              string userItem = splitstring[1] + "," + splitstring[2];
              AddItemToListView(userItem);
              break;
            case "logout":
              RemoveItemFromListView(splitstring[1]);
              break;
            case "talk":
              for (int i = 0; i < chatFormList.Count; i++)
              {
                if (chatFormList[i].Text == splitstring[2])
                {
                  chatFormList[i].ShowTalkInfo(splitstring[2], splitstring[1], splitstring[3]);
                }
              }

              break;
          }
        }
        catch
        {
          break;
        }
      }
    }

    // 从服务器获取在线用户列表
    private void GetUserList()
    {
      while (true)
      {
        userListstring = null;
        try
        {
          userListstring = binaryReader.ReadString();
          if (userListstring.EndsWith("end"))
          {
            string[] splitstring = userListstring.Split(';');
            for (int i = 0; i < splitstring.Length - 1; i++)
            {
              AddItemToListView(splitstring[i]);
            }

            binaryReader.Close();
            tcpClient.Close();
            break;
          }
        }
        catch
        {
          break;
        }
      }
    }
  // 发送登录请求
    private void SendMessage(object obj)
    {
      string message = (string)obj;
      byte[] sendbytes = Encoding.Unicode.GetBytes(message);
      IPAddress remoteIp = IPAddress.Parse(txtserverIP.Text);
      IPEndPoint remoteIPEndPoint = new IPEndPoint(remoteIp, int.Parse(txtServerport.Text));
      sendUdpClient.Send(sendbytes, sendbytes.Length, remoteIPEndPoint);
      sendUdpClient.Close();
    }