Question

我已经停留了一段时间了，当从客户端向服务器发送请求时，服务器响应从sql数据库中提取的数据并且客户端收到它，一切正常。问题是当客户端再次向服务器请求数据时，这会给我以下错误：对象引用未设置为对象实例。事实上，在向我的数据库添加数据时，服务器可以接收多个请求。根据我的尝试捕获，当我的SendCallback调用我的方法来开始接收数据时发生错误。

private static void BeginAccept()
    {
        listener.Listen(5);

        Thread t = new Thread(() =>
        listener.BeginAccept(new AsyncCallback(AcceptCallback), listener));
        t.Start();
    }

private static void AcceptCallback(IAsyncResult ar)
    {
        Socket listener = (Socket)ar.AsyncState;
        Socket handler = listener.EndAccept(ar);

        handler.BeginReceive(recBuf, 0, bufsize, 0, new AsyncCallback(ReceiveCallback), handler);

        Console.WriteLine("client connected"  );
    }

private static void ReceiveCallback(IAsyncResult ar)
    {
        try
        {
            Console.WriteLine("Waiting for data...");

            string content = string.Empty;
            string[] pieces = null;
            string[] delimiters = { "|" };
            /*StateObject state = (StateObject)ar.AsyncState; */// Calling the socket from AcceptCallback.
            Socket handler = (Socket)ar.AsyncState;
            sb.Clear();
            int dataReceived = handler.EndReceive(ar);

                if (dataReceived > 0)
                {
                   sb.Append(Encoding.ASCII.GetString(recBuf, 0,dataReceived));
                    if (content.IndexOf("<!ReqDB>") > -1)
                    {
                        try
                        {
                            Console.WriteLine("Following data received: " + content);
                            pieces = null;
                            pieces = content.Split(delimiters, StringSplitOptions.None);
                            sb = null;
                            Console.WriteLine("ReqDB received!!");
                            Int64 ID = Int64.Parse(pieces[0]);
                            RetrieveDataFromDB(handler, ID);
     //Some other irrelevant code....

RetrieveDataFromDB将数据从数据库中提取出来，转换它并调用Send（处理程序，数据）;

private static void Send(Socket handler, string data)
    {
        byte[] byteData = Encoding.ASCII.GetBytes(data);

        handler.BeginSend(byteData, 0, byteData.Length, 0, new AsyncCallback(SendCallback), handler);
    }

private static void SendCallback(IAsyncResult ar)
    {
        try
        {
            Socket handler = (Socket)ar.AsyncState;
            byte[] buffer = new byte[1024];
            int bytesSend = handler.EndSend(ar);
            handler.BeginReceive(recBuf, 0, bufsize, 0, new AsyncCallback(ReceiveCallback), handler);

        }
        catch (Exception e)
        {
            Console.WriteLine("Line 197: "+e.ToString());
        }
    }

某处，可能当SendCallback执行handler.beginReceive并调用该方法时，会发生错误，我不知道错误在哪里，或者导致错误的原因。我认为它是处理程序，但我不明白为什么它会导致它。

再次开始接收套接字错误

0 个答案: