先來講述下我自己對于整個Socket通信過程的理解，畢竟初學，說錯見諒，知道錯了會改正~ 

首先在服務端新建一個serverSocket，對其進行初始化（一般包含AddressFamily:IP地址類型，SocketType:Socket傳輸數據方式，ProtoType:傳輸協議）; 

接著我們要設置server端要綁定的IP:port;然后開始監聽，并設置最多同時監聽多少個Client.

這時，服務端就在等待狀態，直到某一個Client連接到這個ip:port上，這時serverSocket.Accept()工作，獲得這個連接。（此時的連接是有地址信息的哦！記得保存） 

獲得連接之后，server就可以和這個Client進行通信了,當加入第二個Client（我們稱其為ClientB）時，Server接收到ClientB的消息，可以將這個消息轉發給前一個Client（我們稱其為ClientA），當受到ClientA的消息，也可以轉發給ClientB。這樣就實現了Clients之間的通信了。（重點在保存連接信息！！）

那么現在貼上代碼講解：

Server端代碼 

namespace SocketServer{  class Program  {    private static byte[] result = new byte[1024];       static Socket serverSocket;    private static string client;    private static Socket clientSocket;    //我這里存了兩個Client，因為自己電腦開了兩個Client，不會有多的    //理論上應該開一個Socket[]來保存信息，最好用一個二元組將client的信息和連接綁定起來    //這樣就可以實現斷開連接后下次登陸還是可以識別是這個Client    private static Socket clientSocketA=null;    private static Socket clientSocketB=null;        static void Main(string[] args)    {      Program.SetPort(8885);    }    private static void SetPort(int port)    {      IPAddress ip = IPAddress.Parse("127.0.0.1");//set ip      serverSocket = new Socket(AddressFamily.InterNetwork,        SocketType.Stream, ProtocolType.Tcp);//initialize      serverSocket.Bind(new IPEndPoint(ip, port));//bind      serverSocket.Listen(10);      //進入監聽狀態      Console.WriteLine("監聽{0}成功", serverSocket.LocalEndPoint.ToString());      //開啟一個線程來監聽客戶端連接      Thread myThread = new Thread(ListenClientConnect);      myThread.Start();      Console.ReadLine();    }    /// <summary>    /// 監聽客戶端連接    /// </summary>    private static void ListenClientConnect()    {      while (true)      {        //Client連接上后 得到這個連接        clientSocket = serverSocket.Accept();        //這里我因為只有兩個Client，所以就簡單寫了        if (clientSocketA == null)        {          clientSocketA = clientSocket;        }        else if (clientSocketB == null)        {          clientSocketB = clientSocket;        }        else        {          //當其中一個斷開了，又重新連接時，需要再次保存連接          if (clientSocketB.IsBound)          {            clientSocketA = clientSocketB;            clientSocketB = clientSocket;          }          else          {            clientSocketB = clientSocketA;            clientSocketA = clientSocket;          }                  }        clientSocket.Send(Encoding.ASCII.GetBytes("say hello"));        //開個線程接收Client信息        Thread receivedThread = new Thread(ReceiveMessage);        receivedThread.Start(clientSocket);      }    }       private static void ReceiveMessage(object clientSocket)    {      Socket myClientSocket = (Socket) clientSocket;            while (true)      {        try        {          int revceiveNumber = myClientSocket.Receive(result);          //Console.WriteLine("接受客戶端{0}消息{1}", myClientSocket.RemoteEndPoint.ToString()          //  , Encoding.ASCII.GetString(result, 0, revceiveNumber));          Console.WriteLine(Encoding.ASCII.GetString(result, 0, revceiveNumber));          if (myClientSocket == clientSocketA)          {            Console.WriteLine("receive from A");            if (clientSocketB!=null&&clientSocketB.IsBound)            {              Console.WriteLine("a IS BOUND");              clientSocketB.Send(result, 0, revceiveNumber, SocketFlags.None);            }            else            {              myClientSocket.Send(Encoding.ASCII.GetBytes("the people is not online! Send Failed!"));              Console.WriteLine("對方不在線上，發送失敗！");            }          }          else          {            Console.WriteLine("receive from B");            if (clientSocketA != null && clientSocketA.IsBound)            {              Console.WriteLine("a IS BOUND");              clientSocketA.Send(result, 0, revceiveNumber, SocketFlags.None);            }              else            {              myClientSocket.Send(Encoding.ASCII.GetBytes("the people is not online! Send Failed!"));              Console.WriteLine("對方不在線上，發送失敗！");            }          }                  }        catch(Exception ex)        {          Console.WriteLine(ex.Message);          myClientSocket.Shutdown(SocketShutdown.Both);          myClientSocket.Close();          break;        }      }    }  }}