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Question

我想实现一个异步服务器套接字。为此，我正在研究Microsoft Docs。还有一些我不理解的东西。

有一个回调函数调用ReceiveCallback。而且据我所知，每次收到消息时都会调用此函数。但是为什么我们要检查bytesRead > 0是否呢？这将意味着未收到任何消息，并且如果未收到任何消息，则不会调用回调函数。结果，我再也没进入else condition并且我的response从未设置过...

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, 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());  
    }  
}