另见Understand the NetworkStream.EndRead() example from MSDN。
我正在尝试使用BeginRead
和EndRead
方法从NetworkStream异步读取(具体来说,我想打开一个NetworkStream,执行各种其他任务,然后处理在NetworkStream上收到的数据)。 EndRead
(here)的MSDN示例存在各种问题,并且如链接问题中所述,不能正常工作。该问题的答案显示了如何构建基本代码,但它不包括回调中来自NetworkStream的实际数据读取。
在回调函数中,如何将从NetworkStream读取的数据传输到缓冲区?
编辑
这是原始的MSDN示例。
public static void myReadCallBack(IAsyncResult ar )
{
NetworkStream myNetworkStream = (NetworkStream)ar.AsyncState;
byte[] myReadBuffer = new byte[1024];
String myCompleteMessage = "";
int numberOfBytesRead;
numberOfBytesRead = myNetworkStream.EndRead(ar);
myCompleteMessage = String.Concat(myCompleteMessage,Encoding.ASCII.GetString(myReadBuffer, 0, numberOfBytesRead));
// message received may be larger than buffer size so loop through until you have it all.
while(myNetworkStream.DataAvailable)
{
myNetworkStream.BeginRead(myReadBuffer, 0, myReadBuffer.Length, new AsyncCallback(NetworkStream_ASync_Send_Receive.myReadCallBack), myNetworkStream);
}
// Print out the received message to the console.
Console.WriteLine("You received the following message : " + myCompleteMessage);
}
此示例的基本问题是没有数据从NetworkStream传输到myReadBuffer
。
编辑1
感谢Dmytro Mukalov,以下代码有效:
internal class CallbackArgs
{
public NetworkStream Stream { get; set; }
public byte[] Buffer { get; set; }
public CallbackArgs(NetworkStream stream, byte[] buffer)
{
Stream = stream;
Buffer = buffer;
}
}
// In the caller:
// (Create and open thisNetworkStream, and check thisNetworkStream.CanRead)
byte[] thisReadBuffer = new byte[1024];
CallbackArgs args = new CallbackArgs(thisNetworkStream, thisReadBuffer);
thisNetworkStream.BeginRead(thisReadBuffer, 0, thisReadBuffer.Length, new AsyncCallback(myReadCallBack), args);
// The callback function:
public static void myReadCallBack(IAsyncResult ar)
{
CallbackArgs args = (CallbackArgs)ar.AsyncState;
NetworkStream myNetworkStream = args.Stream;
byte[] myReadBuffer = args.Buffer;
// myReadBuffer now contains the data read from the network stream.
int bytesRead = myNetworkStream.EndRead(ar);
// Do work on myReadBuffer, etc.
}
当正在执行回调时,数据已经传输到传递给前面的BeginRead
调用的缓冲区中。给出示例的问题是它试图使用本地myReadBuffer
缓冲区来读取初始消息。相反,你应该将传递给BeginRead
的缓冲区传递给EndRead
。您可以通过将其作为此缓冲区的类的实例成员,将其与NetworkStream
作为state
的BeginRead
参数一起传递,在某些方法中使用闭包变量来启动读取循环等来实现。