TCP通信需要通信雙方都在線，所以需要先啟動服務端進行監聽，客戶端才能獲得連接，服務端代碼：

 static void Main(string[] args)        {            TcpClient client = null;            NetworkStream stream = null;            byte[] buffer = null;            string receiveString = null;            ipAddress localIP = IPAddress.Parse("127.0.0.1");            int localPort = 11000;            TcpListener listener = new TcpListener(localIP, localPort);//用本地IP和端口實例化Listener            listener.Start();//開始監聽            while (true)            {                client = listener.AcceptTcpClient();//接受一個Client                buffer = new byte[client.ReceiveBufferSize];                stream = client.GetStream();//獲取網絡流                stream.Read(buffer, 0, buffer.Length);//讀取網絡流中的數據                stream.Close();//關閉流                client.Close();//關閉Client                receiveString = Encoding.Default.GetString(buffer).Trim('/0');//轉換成字符串                Console.WriteLine(receiveString);            }        }

只有服務端開啟監聽后，客戶端才能正確連接，所以服務端要一直開啟監聽，客戶端每次發送數據，都要首先與服務端建立連接，連接建立完成后才進行數據發送。客戶端代碼：

static void Main(string[] args)        {            string sendString = null;//要發送的字符串            byte[] sendData = null;//要發送的字節數組            TcpClient client = null;//TcpClient實例            NetworkStream stream = null;//網絡流            IPAddress remoteIP = IPAddress.Parse("127.0.0.1");//遠程主機IP            int remotePort = 11000;//遠程主機端口            while (true)//死循環            {                sendString = Console.ReadLine();//獲取要發送的字符串                sendData = Encoding.Default.GetBytes(sendString);//獲取要發送的字節數組                client = new TcpClient();//實例化TcpClient                try                {                    client.Connect(remoteIP, remotePort);//連接遠程主機                }                catch (System.Exception ex)                {                    Console.WriteLine("連接超時，服務器沒有響應！");//連接失敗                    Console.ReadKey();                    return;                }                stream = client.GetStream();//獲取網絡流                stream.Write(sendData, 0, sendData.Length);//將數據寫入網絡流                stream.Close();//關閉網絡流                client.Close();//關閉客戶端            }        }