c＃异步套接字程序。不执行接收数据的回调

Question

我按照此链接https://msdn.microsoft.com/en-us/library/bew39x2a(v=vs.110).aspx进行异步套接字编程。

从不调用ReceiveCallback func的其他部分。当有任何数据时，它在if（bytesRead＆gt; 0）部分中被接收。在if循环中，为了获得剩余的数据，再次调用BeginReceive。但是根本没有收到对此的回调。

 private static void ReceiveCallback( IAsyncResult ar ) {
        try {
            // Retrieve the state object and the client socket 
            // from the asynchronous state object.
            StateObject state = (StateObject) ar.AsyncState;
            Socket client = state.workSocket;

            // Read data from the remote device.
            int bytesRead = client.EndReceive(ar);

            if (bytesRead > 0) {
                // There might be more data, so store the data received so far.
            state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead));

                // Get the rest of the data.
                client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,
                    new AsyncCallback(ReceiveCallback), state);
            } else {
                // All the data has arrived; put it in response.
                if (state.sb.Length > 1) {
                    response = state.sb.ToString();
                }
                // Signal that all bytes have been received.
                receiveDone.Set();
            }
        } catch (Exception e) {
            Console.WriteLine(e.ToString());
        }
    }