TcpClient.connect给出错误 [英] TcpClient.connect giving error

问题描述

我正在编写一个应用程序，以与服务器之间收发一些数据.我需要在发送一些数据之前进行连接，并且需要保持打开状态，以便用户可以连续发送数据.用户可以通过单击断开按钮随时关闭连接.我创建了2个按钮，一个用于连接，另一个用于断开连接.断开按钮后面的代码如下:-

I am writing an application to send/receive some data to and from a server. I need to make a connection before sending some data and need to keep it open so that user can send data continuously. The user can close the connection at any time by clicking on disconnect button. I created 2 buttons, one to connect and one to disconnect. Code behind Disconnect button is as below:-

private void button1_Click(object sender, EventArgs e)
    {
        if (tcpclnt.Connected)
        {
            tcpclnt.Client.Disconnect(false);
            stm.Close();
        }
        else
        {
            MessageBox.Show("Not Connected");
        }
    }

连接按钮后面的代码如下:-

code behind connect button is as below:-

public ASCIIEncoding asen = new ASCIIEncoding();
public TcpClient tcpclnt = new TcpClient();
public NetworkStream stm;

private void Connect_Click(object sender, EventArgs e)
{
    if (!tcpclnt.Connected)
    {
        tcpclnt.Connect("XX.XX.XX.XX", 5500);
        MessageBox.Show("Connected to server");


        stm = tcpclnt.GetStream();

        string sysname = "000B0000" + SystemName.Text.ToString();
        byte[] sys1 = asen.GetBytes(sysname);
        sys1[0] = 0; sys1[1] = 0;
        sys1[2] = 0; sys1[3] = 0xB;
        sys1[4] = 0; sys1[5] = 0;
        sys1[6] = 0; sys1[7] = 0;
        try
        {
            stm.Write(sys1, 0, sys1.Length);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
            MessageBox.Show("Error in Sending data");
        }
        if (stm.DataAvailable)
        {
            try
            {
                byte[] bb = new byte[600];
                int k = 8;
                k = stm.Read(bb, 0, bb.Length);
                string value = ASCIIEncoding.ASCII.GetString(bb, 8, k - 8);
                MessageBox.Show(value.ToString());
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
                MessageBox.Show("Error in Reading data");
            }
        }
     }
     else {
            MessageBox.Show("Already Connected");
    }
}

现在，当我单击连接"按钮时，它已连接到服务器并且工作正常.现在，当我单击断开连接"按钮并再次单击连接"按钮以建立连接时，它会在tcpclient.connect行上引发异常.我不明白为什么或如何解决该问题，请提出建议.

Thnx，
A

Now, when I click on connect button it connects to server and works fine. Now when I clieck on Disconnect button and again click on connect button to make the connection, it''s throwing an exception on tcpclient.connect line. I don''t understand why or how can I solve it, Please suggest.

Thnx,
A

推荐答案

请参阅我对问题的评论.您应该提供全面的异常信息.但是首先，请检查服务器端发生了什么.客户端断开连接后，服务器可能无法恢复运行.这是初学者的典型错误.您是否在服务器上创建了两个网络线程，一个用于侦听和接受新连接，另一个用于从网络流或远程套接字读取/写入.另外，第二个(通信)线程的代码应从断开连接引起的异常中恢复.

因此，如果服务器部分有问题，可能会出现两个问题:1)在第一次连接然后断开连接之后，不再有代码在监听连接了； 2)客户端断开连接导致服务器端异常；在此异常之后，通信线程不再通信.请检查全部.



谢谢您的澄清.客户端有问题.
首先，请注意，TcpClient实现了System.IDisposable，但是在断开连接后，您忘记了使用TcpClient的实例调用Dispose.它不像一个新的.另外，尝试在每个连接tcpclnt = new TcpClient()之前创建一个新实例.

—SA

Please see my comment to the question. You should provide comprehensive exception information. But first, check up what happens on the server side. It''s possible that the server is not designed to resume operation after a client is disconnected; this is a typical mistake of the beginners. Did you create two network threads on the server, one for listening and accepting new connections, and another one for reading/writing from/to network streams or remote sockets. Also, the code of the second (communication) thread should recover from an exception caused by disconnection.

So, if the server part is wrong, there could be two problems: 1) no code is listening for a connection anymore after first connection and then disconnection; 2) the disconnection by the client side cause exception on the server side; and after this exception the communication thread not communicating anymore. Please check up it all.



Thank you for clarification. There is a problem on client side.
First, pay attention, TcpClient implements System.IDisposable, but you forgot to call Dispose with the instance of the TcpClient after you disconnected. It is not like a new one. Also, try to create a new instance before each connection, tcpclnt = new TcpClient().

—SA

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