如何修复System.dll中发生的类型为“System.InvalidOperationException”的未处理异常 [英] How can fix the An unhandled exception of type 'System.InvalidOperationException' occurred in System.dll

问题描述

public void Start()
{
    _listener = new TcpListener(IPAddress.Any, 21);
    _listener.Start();
    _listener.BeginAcceptTcpClient(HandleAcceptTcpClient, _listener);
}

public void Stop()
{
    if (_listener != null)
    {
        _listener.Stop();
    }
}
private void HandleAcceptTcpClient(IAsyncResult result)
{
    TcpClient client = _listener.EndAcceptTcpClient(result);
    _listener.BeginAcceptTcpClient(HandleAcceptTcpClient, _listener);

    Iplist.Add(((IPEndPoint)client.Client.RemoteEndPoint).Address.ToString());
    lstBox1.Items.Add(Iplist[0]);

}

i希望得到哪个客户端的ip连接我的ftp服务器并将其写入列表框。



我试图将ips添加到array.There没有问题，但是我想将这个数组项添加到listbox我得到了这个异常类型'系统未处理的异常.InvalidOperationException'发生在System.dll，我无法解决它。我怎么能修复它？

i want to get which client's ip connected my ftp server and i write it to listbox.

I tried to add ips to array.There is no problem, However i want to add this arrays item to listbox I got this exception "An unhandled exception of type 'System.InvalidOperationException' occurred in System.dll" and i cant fix it.How can i fix it?

推荐答案

试试这个：

private void HandleAcceptTcpClient(IAsyncResult result)
{
    // put a break-point here and observe what happens

    TcpClient client = _listener.EndAcceptTcpClient(result);
    _listener.BeginAcceptTcpClient(HandleAcceptTcpClient, _listener);

    IPEndPoint ipEnd = client.Client.RemoteEndPoint as IPEndPoint;

    // put a break-point here and observe what happens
    if (ipEnd != null)
    {
        Iplist.Insert(0, ipEnd.Address.ToString());
        lstBox1.Items.Add(Iplist[0]);
    }
    else
    {
        throw new ArgumentNullException("ipEnd is null");
    }
}

如图所示放置断点，然后单步执行代码以查找错误发生的位置，以及错误发生前关键变量的值。

Put break-points as shown, and single step through the code looking for where the error occurs, and what the values of key variables are before the error occurs.

由于以下原因而发生：

1.如果不指定数据源或服务器，则无法打开连接。或者

2.连接已经打开。



检查

It occurs because of following reasons:
1. Cannot open a connection without specifying a data source or server. or
2. The connection is already open.

check it

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