在使用TcpListener/TcpClient同步编程之前，要引入两个命名空间

using System.Net;
using System.Net.Sockets;

服务器代码示例：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;

namespace Net
{
    class Program
    {
        static void Main(string[] args)
        {
            //服务端对端口进行侦听：
            TcpListener listener = new TcpListener(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 10001));
            listener.Start();
            //检测来自客户端的连接请求
            Console.WriteLine("等待连接请求...........");
            TcpClient remoteClient = listener.AcceptTcpClient();
            Console.WriteLine("连接到客户端!!!");
            //建立和连接的客户端的数据流(传输数据)
            NetworkStream streamFromClient = remoteClient.GetStream();
            //创建缓存区
            byte[] buffer = new byte[8096];

            //每次读取缓存中的大小
            int byteRead;
            try
            {
                //为了保证数据的完整性以及安全性锁定数据流
                //读取客户端发送来的数据
                lock (streamFromClient)
                {
                    byteRead = streamFromClient.Read(buffer, 0, 8096);
                    Console.WriteLine(DateTime.Now +":收到来自客户端的消息:"+Encoding.Unicode.GetString(buffer, 0, byteRead));
                }

                //向连接的客户端发送数据
                lock (streamFromClient)

                {
                    //buffer为发送的字符数组
                    streamFromClient.Write(buffer,0, buffer.Length);                  

                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }

            streamFromClient.Dispose();
            remoteClient.Close();

            Console.ReadLine();
        }
    }
}

客户端代码示例：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Sockets;

namespace Client
{
    class Program
    {
        static void Main(string[] args)
        {
            TcpClient tcpClient = new TcpClient();
            tcpClient.Connect("127.0.0.1", 10001);
            if (tcpClient.Connected)
            {
                NetworkStream streamFromServer = tcpClient.GetStream();
                byte[] buffer = Encoding.Unicode.GetBytes("hello world Unity");
                int byteRead;
                try
                {
                    lock (streamFromServer)
                    {
                        //发送到服务器
                        streamFromServer.Write(buffer, 0, buffer.Length);
                        buffer = new byte[8096];
                        
                    }
                    lock (streamFromServer)
                    {
                        byteRead = streamFromServer.Read(buffer, 0, 8096);
                        Console.WriteLine(DateTime.Now + "收到来自服务器的消息:" + Encoding.Unicode.GetString(buffer, 0, byteRead));
                    }
                }
                catch (Exception e)
                {
                    Console.WriteLine(e.Message);
                }
            }
            Console.ReadLine();
        }
    }
}