Question

C# BeginReceive（）函数

client.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveMessage), client);
其中ReceiveMessage是回调函数，我想让ReceiveMessage传参数该怎么办
client.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveMessage（ar,label1）), client);会报错，能传参数吗

Answer 1

在各种行为的回调函数中，所对应的socket都从输入参数的AsyncState属性获得。使用（Socket）或者（StateObject）进行强制转换。BeginReceive函数使用的容器为state，因为它需要存放传送的数据。

而其余接收或发送函数的容器为socket也可。代码如下：

 

using System;
 using System.Net;
 using System.Net.Sockets;
using System.Text;
using System.Threading;
// State object for reading client data asynchronously
public class StateObject
{
    // Client  socket.
    public Socket workSocket = null;
    // Size of receive buffer.
    public const int BufferSize = 1024;
    // Receive buffer.
    public byte[] buffer = new byte[BufferSize];
    // Received data string.
    public StringBuilder sb = new StringBuilder();
}
public class AsynchronousSocketListener
{
    // Thread signal.
    public static ManualResetEvent allDone = new ManualResetEvent(false);
    public AsynchronousSocketListener()
    {
    }
    public static void StartListening()
    {
        // Data buffer for incoming data.
        byte[] bytes = new Byte[1024];
        // Establish the local endpoint for the socket.
        // The DNS name of the computer
        // running the listener is "host.contoso.com".
        //IPHostEntry ipHostInfo = Dns.Resolve(Dns.GetHostName());
        IPAddress ipAddress = IPAddress.Parse("192.168.1.104");
        IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);
        // Create a TCP/IP socket.
        Socket listener = new Socket(AddressFamily.InterNetwork,
            SocketType.Stream, ProtocolType.Tcp);
        // Bind the socket to the local endpoint and listen for incoming connections.
        try
        {
            listener.Bind(localEndPoint);
            listener.Listen(100);
            while (true)
            {
                // Set the event to nonsignaled state.
                allDone.Reset();
                // Start an asynchronous socket to listen for connections.
                Console.WriteLine("Waiting for a connection");
                listener.BeginAccept(
                    new AsyncCallback(AcceptCallback),
                    listener);
                // Wait until a connection is made before continuing.
                allDone.WaitOne();
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
        Console.WriteLine("\nPress ENTER to continue");
        Console.Read();
    }
    public static void AcceptCallback(IAsyncResult ar)
    {
       // Signal the main thread to continue.
        allDone.Set();
        // Get the socket that handles the client request.
        Socket listener = (Socket)ar.AsyncState;
        Socket handler = listener.EndAccept(ar);
 
        // Create the state object.
        StateObject state = new StateObject();
        state.workSocket = handler;
        handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);
    }
    public static void ReadCallback(IAsyncResult ar)
    {
        String content = String.Empty;
     
        // Retrieve the state object and the handler socket
        // from the asynchronous state object.
        StateObject state = (StateObject)ar.AsyncState;
        Socket handler = state.workSocket;
        // Read data from the client socket. 
        int bytesRead = handler.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));
            // Check for end-of-file tag. If it is not there, read 
            // more data.
            content = state.sb.ToString();
            if (content.IndexOf("<EOF>") > -1)
            {
                // All the data has been read from the 
                // client. Display it on the console.
                Console.WriteLine("Read {0} bytes from socket. \n Data : {1}",content.Length, content);
                // Echo the data back to the client.
                Send(handler, content);
            }
            else
            {
                // Not all data received. Get more.
                handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, new AsyncCallback(ReadCallback), state);
            }
        }
    }
    private static void Send(Socket handler, String data)
    {
        // Convert the string data to byte data using ASCII encoding.
        byte[] byteData = Encoding.ASCII.GetBytes(data);
        // Begin sending the data to the remote device.
        handler.BeginSend(byteData, 0, byteData.Length, 0,
            new AsyncCallback(SendCallback), handler);
    }
    private static void SendCallback(IAsyncResult ar)
    {
        try
        {
            // Retrieve the socket from the state object.
            Socket handler = (Socket)ar.AsyncState;
            // Complete sending the data to the remote device.
            int bytesSent = handler.EndSend(ar);
            Console.WriteLine("Sent {0} bytes to client.", bytesSent);
            handler.Shutdown(SocketShutdown.Both);
            handler.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }
    }
    public static int Main(String[] args)
    {
        StartListening();
        return 0;
    }
}

Answer 2

AsyncCallback委托只接受一个 System.IAsyncResult 类型的参数。

如果需要传递参数我一般会直接写匿名函数，比如

public int Receive()
{
    byte[] a = null;
    int b;
    string c;
    client.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None,
    (System.IAsyncResult ar) =>
    {
        a = c.Split(' ');
        b = 100;
        // 怎么写都可以
    }, client);
}