c检测到tcp断开连接

我有两个简单的应用程序：

• 服务器应用程序，在特定的tcp端口上等待客户端连接。然后听他说什么，发回一些反馈，并断开客户的连接。

• 一个连接到服务器应用程序的Form应用程序，然后说一些话，然后等待反馈并断开与服务器的连接，然后在表单中显示反馈。

尽管服务器应用程序似乎运行正常(我用Telnet测试过它，我看到了反馈，我看到反馈后直接发生断开连接(，但表单应用程序似乎没有注意到与服务器的断开连接。(TcpClient.Connected似乎即使在服务器断开连接后也保持不变(

我的问题是：为什么是TcpClient。连接保持真实，我如何知道服务器是否/何时断开连接？

这是我的完整代码：

表格申请：

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Windows.Forms;
using System.Threading;
namespace Sender
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void sendButton_Click(object sender, EventArgs e)
        {
            TcpClient tcpClient = new TcpClient();
            tcpClient.Connect(IPAddress.Parse("127.0.0.1"), 81);
            responseLabel.Text = "waiting for response...";
            responseLabel.Invalidate();
            // write request
            NetworkStream networkStream = tcpClient.GetStream();
            byte[] buffer = (new ASCIIEncoding()).GetBytes("Hello World! ");
            networkStream.Write(buffer, 0, buffer.Length);
            networkStream.Flush();
            // read response
            Thread readThread = new Thread(new ParameterizedThreadStart(ReadResponse));
            readThread.Start(tcpClient);
        }
        void ReadResponse(object arg)
        {
            TcpClient tcpClient = (TcpClient)arg;
            StringBuilder stringBuilder = new StringBuilder();
            NetworkStream networkStream = tcpClient.GetStream();
            bool timeout = false;
            DateTime lastActivity = DateTime.Now;
            while (tcpClient.Connected && !timeout)
            {
                if (networkStream.DataAvailable)
                {
                    lastActivity = DateTime.Now;
                    while (networkStream.DataAvailable)
                    {
                        byte[] incomingBuffer = new byte[1024];
                        networkStream.Read(incomingBuffer, 0, 1024);
                        char[] receivedChars = new char[1024];
                        (new ASCIIEncoding()).GetDecoder().GetChars(incomingBuffer, 0, 1024, receivedChars, 0);
                        stringBuilder.Append(receivedChars);
                    }
                }
                else
                {
                    if (DateTime.Now > lastActivity.AddSeconds(60))
                        timeout = true;
                }
                System.Threading.Thread.Sleep(50);
            }
            Invoke((MethodInvoker)delegate
            {
                responseLabel.Text = "Response from Listener:'n" + stringBuilder.ToString();
                responseLabel.Invalidate();
            });
            if (timeout)
            {
                Console.Write("A timeout occured'n");
                networkStream.Close();
                tcpClient.Close();
            }
        }
    }
}

服务器应用程序：

using System.Net;
using System.Net.Sockets;
using System.Text;
using System;
using System.Threading;
namespace Listener
{
    class Program
    {
        static void Main(string[] args)
        {
            var tcpListener = new TcpListener(IPAddress.Any, 81);
            tcpListener.Start();
            Thread clientThread = new Thread(new ParameterizedThreadStart(Listen));
            clientThread.Start(tcpListener);
        }
        static void Listen(object arg)
        {
            TcpListener tcpListener = (TcpListener)arg;
            while (true)
            {
                TcpClient tcpClient = tcpListener.AcceptTcpClient();
                Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClient));
                clientThread.Start(tcpClient);
            }
        }
        static void HandleClient(object arg)
        {
            TcpClient tcpClient = (TcpClient)arg;
            StringBuilder stringBuilder = new StringBuilder();
            ASCIIEncoding encoder = new ASCIIEncoding();
            DateTime lastActivity = DateTime.Now;
            // read request
            NetworkStream networkStream = tcpClient.GetStream();
            int timeout = 5; // gives client some time to send data after connecting
            while (DateTime.Now < lastActivity.AddSeconds(timeout) && stringBuilder.Length==0)
            {
                if (!networkStream.DataAvailable)
                {
                    System.Threading.Thread.Sleep(50);
                }
                else
                {
                    while (networkStream.DataAvailable)
                    {
                        lastActivity = DateTime.Now;
                        byte[] incomingBuffer = new byte[1024];
                        networkStream.Read(incomingBuffer, 0, 1024);
                        char[] receivedChars = new char[1024];
                        encoder.GetDecoder().GetChars(incomingBuffer, 0, 1024, receivedChars, 0);
                        stringBuilder.Append(receivedChars);
                    }
                }
            }
            string request = stringBuilder.ToString();
            // write response
            string response = "The listener just received: " + request;
            byte[] outgoingBuffer = encoder.GetBytes(response);
            networkStream.Write(outgoingBuffer, 0, outgoingBuffer.Length);
            networkStream.Flush();
            networkStream.Close();
            tcpClient.Close();
        }
    }
}