C# socket编程解决办法

C# socket编程
socket中如何判断一个已连接的用户退出,并清空登陆上来的记录.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Net;
using System.Net.Sockets;

namespace Gps_GateWay
{
   
  public partial class Form1 : Form
  {
  public static ManualResetEvent allDone = new ManualResetEvent(false);
  private Thread th;
  private bool listenerRun = true;
  Socket listener;
  private const int maxsocket = 10;
   
  public Form1()
  {
  InitializeComponent();
  }

  private IPAddress GetLocalIP()
  {
  IPHostEntry iphostentry = Dns.GetHostByName(Dns.GetHostName());
  return iphostentry.AddressList[0];
  }

  private void Listen()
  {
  try
  {
  int port = int.Parse(txtPort.Text);
  IPAddress ipaddress = GetLocalIP();
  IPEndPoint ipendpoint = new IPEndPoint(ipaddress, port);
  listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
  listener.Bind(ipendpoint);
  listener.Listen(50);
  while (listenerRun)
  {
  allDone.Reset();
  listener.BeginAccept(new AsyncCallback(AcceptCallBack), listener);
  allDone.WaitOne();
  }
  }
  catch (Exception Err)
  {
  MessageBox.Show(Err.Message);
  }
  }

  private delegate void GetLstControl(string hostname, string remoteip, string remoteport);

  private void GetLstStr(string hostname, string remoteip, string remoteport)
  {
  lstIP.Items.Add("[" + hostname + "] " + remoteip + ":" + remoteport);
  }


  private void AcceptCallBack(IAsyncResult ar)
  {
  try
  {
  allDone.Set();
  Socket sok = (Socket)ar.AsyncState;
  Socket client = sok.EndAccept(ar);
   
  StateObject state = new StateObject();
  state.workSocket = client;


  EndPoint remoteendpoint = client.RemoteEndPoint;
  IPEndPoint ipendpoint = (IPEndPoint)remoteendpoint;
  string remoteip = ipendpoint.Address.ToString();
  string remoteport = ipendpoint.Port.ToString();

  IPHostEntry iphostentry = Dns.GetHostByAddress(ipendpoint.Address);
  string hostname = iphostentry.HostName;
  GetLstControl getlst = new GetLstControl(GetLstStr);
  this.BeginInvoke(getlst,new object[]{hostname,remoteip,remoteport});

  client.BeginReceive(state.buffer, 0,StateObject.BufferSize,0, new AsyncCallback(ReadCallBack), state);
  }
  catch (Exception Err)
  {
  // MessageBox.Show(Err.Message);
  }
  }

  private delegate void GetRchControl(string str);

  private void GetRchMsg(string str)
  {
  rchMsg.AppendText(str);
  }

  private void ReadCallBack(IAsyncResult ar)
  {
  try
  {
   
  StateObject state = (StateObject)ar.AsyncState;
  Socket hander = state.workSocket;

   
  int readbyte = hander.EndReceive(ar);
  if (readbyte > 0)
  {
  string strcontent = "";
  string str_msg = "";
  string strmsg = "";
  strmsg=Encoding.BigEndianUnicode.GetString(state.buffer, 0, readbyte);
  state.sb.Length = 0;
  state.sb.Append(strmsg);
  strcontent = state.sb.ToString() + "\n";

  EndPoint remoteendpoint = hander.RemoteEndPoint;
  IPEndPoint ipendpoint = (IPEndPoint)remoteendpoint;
  string remoteip = ipendpoint.Address.ToString();
  string remoteport = ipendpoint.Port.ToString();

  IPHostEntry iphostentry = Dns.GetHostByAddress(ipendpoint.Address);
  string hostname = iphostentry.HostName;

  string time = DateTime.Now.ToString();

  str_msg = "(" + time + ") " + hostname + "：" + strcontent + "\n";

  GetRchControl getrch = new GetRchControl(GetRchMsg);
  this.BeginInvoke(getrch, new object[] { str_msg });

  //if (strcontent.IndexOf("1") > -1)
  //{
  // // Send(hander, "发送成功\n");
  // byte[] byteData = Encoding.BigEndianUnicode.GetBytes("发送成功\n");
  // hander.BeginSend(byteData, 0, byteData.Length, 0, new AsyncCallback(SendCallback), hander);
  // hander.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallBack), state);
  //}
  //else
  //{
  // hander.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallBack), state);
  //}
  byte[] byteData = Encoding.BigEndianUnicode.GetBytes("(" + time + ") " + "信息发送成功\n");
  hander.BeginSend(byteData, 0, byteData.Length, 0, new AsyncCallback(SendCallback), hander);
  hander.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallBack), state);
   
  }
   
  }
  catch (Exception Err)
  {
  MessageBox.Show(Err.Message);
  }
  }

  private void Send(Socket handler, String data)
  {
  byte[] byteData = Encoding.BigEndianUnicode.GetBytes(data);
  handler.BeginSend(byteData, 0, byteData.Length, 0,new AsyncCallback(SendCallback), handler);
  }

  private void SendCallback(IAsyncResult ar)
  {

  try
  {

  //Socket handler = (Socket)ar.AsyncState;

  //int bytesSent = handler.EndSend(ar);
   
  //handler.Shutdown(SocketShutdown.Both);

  //handler.Close();
   
  }
  catch (Exception Err)
  {
  MessageBox.Show(Err.Message);
  }
  }

  private void button1_Click(object sender, EventArgs e)
  {
  th = new Thread(new ThreadStart(Listen)); 
  th.Start();
   
  }
  }

  public class StateObject
  {

  public Socket workSocket = null;

  public const int BufferSize = 1024;

  public byte[] buffer = new byte[BufferSize];

  public StringBuilder sb = new StringBuilder();

  }
}

[解决办法]
那你就在client端的程序里作处理。告诉服务器端。
[解决办法]
心跳数据
[解决办法]
ReadCallBack里面不是有try{}catch (Exception Err){} 吗？
你改成

。。。
StateObject state = (StateObject)ar.AsyncState; 
Socket hander = state.workSocket; 

try{}
catch (System.Net.Sockets.SocketException e)
{
。。。
// 客户端连接断开（即hander对象），这里出现异常，你捕捉并处理就是了。
}
catch (Exception Err){}