求助，这是我写的TCPserver，使用第一种方法，因为连接数不多，有一个按钮，
点击想达到侦听和停止侦听的功能，但程序停止侦听后，再次点击就有异常，
想问如何关闭侦听？这是我的代码，基本上是博客园的。

 1 using System;
  2  using System.Collections.Generic;
  3  using System.ComponentModel;
  4  using System.Data;
  5  using System.Drawing;
  6 using System.Text;
  7 using System.Windows.Forms;
  8 using System.Net.Sockets;
  9 using System.Net;
 10 using System.Threading;
 11 using System.Collections; 
 12 
 13 
 14 namespace ServerTCP
 15 {
 16     public partial class Form1 : Form
 17     {
 18 
 19         Socket listener;
 20         Thread acceptThread;
 21         Hashtable sockets = new Hashtable();//用于保存已连接的socket
 22 
 23         public Form1()
 24         {
 25             InitializeComponent();
 26         }
 27 
 28         private void Form1_Load(object sender, EventArgs e)
 29         {
 30             IPHostEntry ipe = Dns.GetHostEntry(Dns.GetHostName());
 31             IPAddress ipa = ipe.AddressList[0];
 32             txtIP.Text = ipa.ToString();
 33             txtPort.Text = "4000";
 34         }
 35 
 36         private void btnListen_Click(object sender, EventArgs e)
 37         {
 38             IPAddress ipa = IPAddress.Parse(txtIP.Text);
 39             int port = int.Parse(txtPort.Text);
 40             IPEndPoint LocalEP = new IPEndPoint(ipa, port);
 41             acceptThread = new Thread(new ThreadStart(AcceptWorkThread));
 42             //if (btnListen.Text == "开始监听")
 43             //{
 44             //    listener = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
 45             //    listener.Bind(LocalEP);
 46             //    listener.Listen(100);
 47 
 48             //    acceptThread.Start();
 49             //    btnListen.Text = "停止监听";
 50             //}
 51             //else
 52             //{
 53             //    btnListen.Text = "开始监听";
 54             //    foreach (DictionaryEntry dic in sockets)
 55             //    {
 56             //        Socket socket = (Socket)dic.Value;
 57             //        socket.Close();
 58             //    }
 59             //    listener.Close();
 60             
 61             //}
 62 
 63             
 64         }
 65 
 66         private void AcceptWorkThread()
 67         {
 68             Thread.CurrentThread.IsBackground = true;
 69             while (true)
 70             {
 71                 Socket accept = listener.Accept();
 72                 IPEndPoint remoEP = (IPEndPoint)accept.RemoteEndPoint;
 73                 string remoIP = remoEP.ToString();
 74                 if (!sockets.Contains(remoIP))
 75                 {
 76                     sockets.Add(remoIP, accept);
 77                 }
 78                 this.Invoke((EventHandler)(delegate  
 79                 {
 80                     lstClients.Items.Add(remoIP); 
 81                 }));
 82                 Thread receiveThread = new Thread(new ParameterizedThreadStart(ReceiveWorkThread));
 83                 receiveThread.Start(accept);
 84             }
 85         }
 86 
 87         private void ReceiveWorkThread(Object obj)
 88         {
 89             Thread.CurrentThread.IsBackground = true;
 90             Socket socket = (Socket)obj;
 91             byte[] buffer = new byte[1024];
 92             while (true)
 93             {
 94                 try
 95                 {
 96                     int recvCount = socket.Receive(buffer);
 97                     if (recvCount > 0)
 98                     {
 99                         IPEndPoint remoEP = (IPEndPoint)socket.RemoteEndPoint;
100                         string recv = remoEP.ToString() + "发送来的消息：" + Encoding.Default.GetString(buffer, 0, recvCount);
101                         this.Invoke((EventHandler)(delegate
102                         {
103                             txtGet.AppendText(recv + "\r\n");
104                         }));
105                         socket.Send(buffer, SocketFlags.None);
106                     }
107                     else//==0
108                     {
109                         IPEndPoint remoEP = (IPEndPoint)socket.RemoteEndPoint;
110                         string remo = remoEP.ToString();
111                         this.Invoke((EventHandler)(delegate
112                         {
113                             lstClients.Items.Remove(remo);
114                         }));
115                         if (sockets.Contains(socket))
116                         {
117                             sockets.Remove(remo);
118                         }
119                         
120                         socket.Close();
121                         break;
122                     }
123                 }
124                catch
125                 {
126                     IPEndPoint remoEP = (IPEndPoint)socket.RemoteEndPoint;
127                     string remo = remoEP.ToString();
128                     this.Invoke((EventHandler)(delegate
129                     {
130                         lstClients.Items.Remove(remo);
131                     }));
132                     if (sockets.Contains(socket))
133                     {
134                         sockets.Remove(remo);
135                     }
136                     socket.Close();
137                     break;
138                 }
139             }
140 
141         }
142 
143         private void btnSnd_Click(object sender, EventArgs e)
144         {
145             if (lstClients.SelectedIndex == -1 || txtSend.Text == "")
146             {
147                 MessageBox.Show("选择客户端和内容不能为空");
148                 return;
149             }
150             string clients = lstClients.SelectedItem.ToString();
151             Socket socket = (Socket)sockets[clients];
152             byte[] buffer = Encoding.Default.GetBytes(txtSend.Text);
153             socket.Send(buffer, SocketFlags.None);
154         }
155     }
156 }