IAsyncResult BeginAccept(AsyncCallback callback, object state);

Socket socket = new Socket(
                  AddressFamily.InterNetwork,
                  SocketType.Stream,
                  ProtocolType.Tcp);
IPEndPoint iep = new IPEndPoint(IPAddress.Any, 8888);
socket.Bind(iep);
socket.Listen(5);
socket.BeginAccept (new AsyncCallback(CallbackAccept), socket);

private void CallbackAccept(IAsyncResult iar)
{
  Socket server = (Socket)iar.AsyncState;
  Socket client = server.EndAccept(iar);
}

private List<TcpClientState> clients;

/// <summary>
   /// 異步TCP服務(wù)器
   /// </summary>
   public class AsyncTcpServer : IDisposable
   {
     #region Fields

     private TcpListener listener;
     private List<TcpClientState> clients;
     private bool disposed = false;

     #endregion

     #region Ctors

     /// <summary>
     /// 異步TCP服務(wù)器
     /// </summary>
     /// <param name="listenPort">監(jiān)聽的端口</param>
     public AsyncTcpServer(int listenPort)
       : this(IPAddress.Any, listenPort)
     {
     }

     /// <summary>
     /// 異步TCP服務(wù)器
     /// </summary>
     /// <param name="localEP">監(jiān)聽的終結(jié)點</param>
     public AsyncTcpServer(IPEndPoint localEP)
       : this(localEP.Address, localEP.Port)
     {
     }

     /// <summary>
     /// 異步TCP服務(wù)器
     /// </summary>
     /// <param name="localIPAddress">監(jiān)聽的IP地址</param>
     /// <param name="listenPort">監(jiān)聽的端口</param>
     public AsyncTcpServer(IPAddress localIPAddress, int listenPort)
     {
       Address = localIPAddress;
       Port = listenPort;
       this.Encoding = Encoding.Default;

       clients = new List<TcpClientState>();

       listener = new TcpListener(Address, Port);
       listener.AllowNatTraversal(true);
     }

     #endregion

     #region Properties

     /// <summary>
     /// 服務(wù)器是否正在運行
     /// </summary>
     public bool IsRunning { get; private set; }
     /// <summary>
     /// 監(jiān)聽的IP地址
     /// </summary>
     public IPAddress Address { get; private set; }
     /// <summary>
     /// 監(jiān)聽的端口
     /// </summary>
     public int Port { get; private set; }
     /// <summary>
     /// 通信使用的編碼
     /// </summary>
     public Encoding Encoding { get; set; }

     #endregion

     #region Server

     /// <summary>
     /// 啟動服務(wù)器
     /// </summary>
     /// <returns>異步TCP服務(wù)器</returns>
     public AsyncTcpServer Start()
     {
       if (!IsRunning)
       {
         IsRunning = true;
         listener.Start();
         listener.BeginAcceptTcpClient(
           new AsyncCallback(HandleTcpClientAccepted), listener);
       }
       return this;
     }

     /// <summary>
     /// 啟動服務(wù)器
     /// </summary>
     /// <param name="backlog">
     /// 服務(wù)器所允許的掛起連接序列的最大長度
     /// </param>
     /// <returns>異步TCP服務(wù)器</returns>
     public AsyncTcpServer Start(int backlog)
     {
       if (!IsRunning)
       {
         IsRunning = true;
         listener.Start(backlog);
         listener.BeginAcceptTcpClient(
           new AsyncCallback(HandleTcpClientAccepted), listener);
       }
       return this;
     }

     /// <summary>
     /// 停止服務(wù)器
     /// </summary>
     /// <returns>異步TCP服務(wù)器</returns>
     public AsyncTcpServer Stop()
     {
       if (IsRunning)
       {
         IsRunning = false;
         listener.Stop();

         lock (this.clients)
         {
           for (int i = 0; i < this.clients.Count; i++)
           {
             this.clients[i].TcpClient.Client.Disconnect(false);
           }
           this.clients.Clear();
         }

       }
       return this;
     }

     #endregion

     #region Receive

     private void HandleTcpClientAccepted(IAsyncResult ar)
     {
       if (IsRunning)
       {
         TcpListener tcpListener = (TcpListener)ar.AsyncState;

         TcpClient tcpClient = tcpListener.EndAcceptTcpClient(ar);
         byte[] buffer = new byte[tcpClient.ReceiveBufferSize];

         TcpClientState internalClient
           = new TcpClientState(tcpClient, buffer);
         lock (this.clients)
         {
           this.clients.Add(internalClient);
           RaiseClientConnected(tcpClient);
         }

         NetworkStream networkStream = internalClient.NetworkStream;
         networkStream.BeginRead(
           internalClient.Buffer,
           0,
           internalClient.Buffer.Length,
           HandleDatagramReceived,
           internalClient);

         tcpListener.BeginAcceptTcpClient(
           new AsyncCallback(HandleTcpClientAccepted), ar.AsyncState);
       }
     }

     private void HandleDatagramReceived(IAsyncResult ar)
     {
       if (IsRunning)
       {
         TcpClientState internalClient = (TcpClientState)ar.AsyncState;
         NetworkStream networkStream = internalClient.NetworkStream;

         int numberOfReadBytes = 0;
         try
         {
           numberOfReadBytes = networkStream.EndRead(ar);
         }
         catch
         {
           numberOfReadBytes = 0;
         }

         if (numberOfReadBytes == 0)
         {
           // connection has been closed
           lock (this.clients)
           {
             this.clients.Remove(internalClient);
             RaiseClientDisconnected(internalClient.TcpClient);
             return;
           }
         }

         // received byte and trigger event notification
         byte[] receivedBytes = new byte[numberOfReadBytes];
         Buffer.BlockCopy(
           internalClient.Buffer, 0,
           receivedBytes, 0, numberOfReadBytes);
         RaiseDatagramReceived(internalClient.TcpClient, receivedBytes);
         RaisePlaintextReceived(internalClient.TcpClient, receivedBytes);

         // continue listening for tcp datagram packets
         networkStream.BeginRead(
           internalClient.Buffer,
           0,
           internalClient.Buffer.Length,
           HandleDatagramReceived,
           internalClient);
       }
     }

     #endregion

     #region Events

     /// <summary>
     /// 接收到數(shù)據(jù)報文事件
     /// </summary>
     public event EventHandler<TcpDatagramReceivedEventArgs<byte[]>> DatagramReceived;
     /// <summary>
     /// 接收到數(shù)據(jù)報文明文事件
     /// </summary>
     public event EventHandler<TcpDatagramReceivedEventArgs<string>> PlaintextReceived;

     private void RaiseDatagramReceived(TcpClient sender, byte[] datagram)
     {
       if (DatagramReceived != null)
       {
         DatagramReceived(this, new TcpDatagramReceivedEventArgs<byte[]>(sender, datagram));
       }
     }

     private void RaisePlaintextReceived(TcpClient sender, byte[] datagram)
     {
       if (PlaintextReceived != null)
       {
         PlaintextReceived(this, new TcpDatagramReceivedEventArgs<string>(
           sender, this.Encoding.GetString(datagram, 0, datagram.Length)));
       }
     }

     /// <summary>
     /// 與客戶端的連接已建立事件
     /// </summary>
     public event EventHandler<TcpClientConnectedEventArgs> ClientConnected;
     /// <summary>
     /// 與客戶端的連接已斷開事件
     /// </summary>
     public event EventHandler<TcpClientDisconnectedEventArgs> ClientDisconnected;

     private void RaiseClientConnected(TcpClient tcpClient)
     {
       if (ClientConnected != null)
       {
         ClientConnected(this, new TcpClientConnectedEventArgs(tcpClient));
       }
     }

     private void RaiseClientDisconnected(TcpClient tcpClient)
     {
       if (ClientDisconnected != null)
       {
         ClientDisconnected(this, new TcpClientDisconnectedEventArgs(tcpClient));
       }
     }

     #endregion

     #region Send

     /// <summary>
     /// 發(fā)送報文至指定的客戶端
     /// </summary>
     /// <param name="tcpClient">客戶端</param>
     /// <param name="datagram">報文</param>
     public void Send(TcpClient tcpClient, byte[] datagram)
     {
       if (!IsRunning)
         throw new InvalidProgramException("This TCP server has not been started.");

       if (tcpClient == null)
         throw new ArgumentNullException("tcpClient");

       if (datagram == null)
         throw new ArgumentNullException("datagram");

       tcpClient.GetStream().BeginWrite(
         datagram, 0, datagram.Length, HandleDatagramWritten, tcpClient);
     }

     private void HandleDatagramWritten(IAsyncResult ar)
     {
       ((TcpClient)ar.AsyncState).GetStream().EndWrite(ar);
     }

     /// <summary>
     /// 發(fā)送報文至指定的客戶端
     /// </summary>
     /// <param name="tcpClient">客戶端</param>
     /// <param name="datagram">報文</param>
     public void Send(TcpClient tcpClient, string datagram)
     {
       Send(tcpClient, this.Encoding.GetBytes(datagram));
     }

     /// <summary>
     /// 發(fā)送報文至所有客戶端
     /// </summary>
     /// <param name="datagram">報文</param>
     public void SendAll(byte[] datagram)
     {
       if (!IsRunning)
         throw new InvalidProgramException("This TCP server has not been started.");

       for (int i = 0; i < this.clients.Count; i++)
       {
         Send(this.clients[i].TcpClient, datagram);
       }
     }

     /// <summary>
     /// 發(fā)送報文至所有客戶端
     /// </summary>
     /// <param name="datagram">報文</param>
     public void SendAll(string datagram)
     {
       if (!IsRunning)
         throw new InvalidProgramException("This TCP server has not been started.");

       SendAll(this.Encoding.GetBytes(datagram));
     }

     #endregion

     #region IDisposable Members

     /// <summary>
     /// Performs application-defined tasks associated with freeing,
     /// releasing, or resetting unmanaged resources.
     /// </summary>
     public void Dispose()
     {
       Dispose(true);
       GC.SuppressFinalize(this);
     }

     /// <summary>
     /// Releases unmanaged and - optionally - managed resources
     /// </summary>
     /// <param name="disposing"><c>true</c> to release
     /// both managed and unmanaged resources; <c>false</c>
     /// to release only unmanaged resources.</param>
     protected virtual void Dispose(bool disposing)
     {
       if (!this.disposed)
       {
         if (disposing)
         {
           try
           {
             Stop();

             if (listener != null)
             {
               listener = null;
             }
           }
           catch (SocketException ex)
           {
             ExceptionHandler.Handle(ex);
           }
         }

         disposed = true;
       }
     }

     #endregion
   }

class Program
   {
     static AsyncTcpServer server;

     static void Main(string[] args)
     {
       LogFactory.Assign(new ConsoleLogFactory());

       server = new AsyncTcpServer(9999);
       server.Encoding = Encoding.UTF8;
       server.ClientConnected +=
         new EventHandler<TcpClientConnectedEventArgs>(server_ClientConnected);
       server.ClientDisconnected +=
         new EventHandler<TcpClientDisconnectedEventArgs>(server_ClientDisconnected);
       server.PlaintextReceived +=
         new EventHandler<TcpDatagramReceivedEventArgs<string>>(server_PlaintextReceived);
       server.Start();

       Console.WriteLine("TCP server has been started.");
       Console.WriteLine("Type something to send to client...");
       while (true)
       {
         string text = Console.ReadLine();
         server.SendAll(text);
       }
     }

     static void server_ClientConnected(object sender, TcpClientConnectedEventArgs e)
     {
       Logger.Debug(string.Format(CultureInfo.InvariantCulture,
         "TCP client {0} has connected.",
         e.TcpClient.Client.RemoteEndPoint.ToString()));
     }

     static void server_ClientDisconnected(object sender, TcpClientDisconnectedEventArgs e)
     {
       Logger.Debug(string.Format(CultureInfo.InvariantCulture,
         "TCP client {0} has disconnected.",
         e.TcpClient.Client.RemoteEndPoint.ToString()));
     }

     static void server_PlaintextReceived(object sender, TcpDatagramReceivedEventArgs<string> e)
     {
       if (e.Datagram != "Received")
       {
         Console.Write(string.Format("Client : {0} --> ",
           e.TcpClient.Client.RemoteEndPoint.ToString()));
         Console.WriteLine(string.Format("{0}", e.Datagram));
         server.Send(e.TcpClient, "Server has received you text : " + e.Datagram);
       }
     }
   }