程序代码：

/// <summary>
        /// 不停的接收服务器发送来的消息
        /// </summary>
        /// <param name="o"></param>
        void Recive(object o)
        {
            try
            {
                Socket socketSend = o as Socket;
                while (true)
                {
                    byte[] buffer = new byte[1024 * 1024 * 3];
                    //实际接收到的有效字节数
                    int r = socketSend.Receive(buffer);
                    if (r == 0)
                    {
                        break;
                    }
                    //发送的文字消息
                    if (buffer[0] == 0)
                    {
                        string s = Encoding.UTF8.GetString(buffer, 1, r - 1);
                        ShowMsg(socketSend.RemoteEndPoint + ":" + s);
                    }
                    if (buffer[0] == 9)
                    {
                    }
                    if (buffer[0] == 1)
                    {
                        SaveFileDialog sfd = new SaveFileDialog();
                        sfd.InitialDirectory = @"C:\Users\Administrator.SKY-20181116FAG\Desktop";
                        sfd.Title = "请选择要保存的文件";
                        sfd.Filter = "所有文件|*.*";
                        sfd.ShowDialog(this);
                        string path = sfd.FileName;
                        using (FileStream fsWrite = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write))
                        {
                            fsWrite.Write(buffer, 1, r - 1);
                        }
                        MessageBox.Show("保存成功");
                    }
                    if (buffer[0] == 2)
                    {
                        ZD();
                    }
                }
            }
            catch { }
        }

程序代码：

//发送消息
        private void btnSend_Click(object sender, EventArgs e)
        {
            try
            {
                string str = this.txtSendMsg.Text.Trim();
                byte[] buffer = System.Text.Encoding.UTF8.GetBytes(str);
                List<byte> list = new List<byte>();
                list.Add(0);
                list.AddRange(buffer);
                //将集合转为数组
                byte[] newbuffer = list.ToArray();

                //判断所有选中项集合大于0
                if (this.lstClient.SelectedItems.Count > 0)
                {
                    //获取选中的值
                    string ip = this.lstClient.SelectedItem.ToString();
                    Console.WriteLine(ip);
                    Console.WriteLine(dicSocket[ip]);
                    dicSocket[ip].Send(newbuffer);
                }
                else
                {
                    MessageBox.Show("未选中listbox集合的值");
                }
            }
            catch { }
            
        }

程序代码：

/// <summary>
        /// 心跳测试
        /// </summary>
        public void HeartbeatClient()
        {
            while (true)
            {
                string str = "69";
                byte[] buffer = System.Text.Encoding.UTF8.GetBytes(str);
                List<byte> list = new List<byte>();
                list.Add(9);
                list.AddRange(buffer);
                //将集合转为数组
                byte[] newbuffer = list.ToArray();
                for (int i = 0; i < lstClient.Items.Count; i++)
                {
                    int flag=0;
                    string ip = lstClient.Items[i].ToString();//获得这一列的IPEndPoint信息
                    if (dicSocket[ip].Connected)
                    {
                        try
                        {
                            flag = dicSocket[ip].Send(newbuffer);//返回的参数是发送到的字节数
                        }
                        catch {}
                    }
                    if (flag <= 0)
                    {
                        ShowMsg(ip + "已掉线。");
                        this.lstClient.Items.Remove(ip);
                    }
                }
            }
            
        }