下面的示例程序创建一个连接到服务器的客户端。该客户端是用异步套接字生成的，因此在等待服务器返回响应时不挂起客户端应用程序的执行。该应用程序将字符串发送到服务器，然后在控制台显示该服务器返回的字符串。

 
C#  复制代码 



using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Text;

// State object for receiving data from remote device.
public static class StateObject {
    // Client socket.
    public static Socket workSocket = null;
    // Size of receive buffer.
    public const int BufferSize = 256;
    // Receive buffer.
    public static byte[] buffer = new byte[BufferSize];
    // Received data string.
    public static StringBuilder sb = new StringBuilder();
}

public static class CClientTCPIP
{
	static int _initCount=0;
        static bool _ifInit = false;
        static string _remoteIP;
        static int _remotePort;
        static Socket clientSocket;
        static EndPoint epServer;
        static byte[] _byteData = new byte[16];
        static string _tcpError;

        public static string TcpError
        {
            get { return _tcpError; }
            set { _tcpError = value; }
        }
        public static byte[] ByteData
        {
            get { return _byteData; }
            set { _byteData = value; }
        }

    

    // ManualResetEvent instances signal completion.
    private static ManualResetEvent connectDone = 
        new ManualResetEvent(false);
    private static ManualResetEvent sendDone = 
        new ManualResetEvent(false);
    private static ManualResetEvent receiveDone = 
        new ManualResetEvent(false);

    // The response from the remote device.
    private static String response = String.Empty;

    public static bool  InitClientTCPIP()
	{
	if (_initCount > 3)
            {
                _tcpError = "连接远程主机时，发生三次连接失败错误！请检查远程主机是否正常运行!重新启动本系统。";
                return false;
            }

        // Connect to a remote device.
        try {
            // Establish the remote endpoint for the socket.
            // The name of the 
            // remote device is "host.contoso.com".
            //IPHostEntry ipHostInfo = Dns.Resolve("host.contoso.com");
            //IPAddress ipAddress = ipHostInfo.AddressList[0];
	    IPAddress ipAddress=IPAddress.Parse(_remoteIP);

            IPEndPoint remoteEP = new IPEndPoint(ipAddress, _remotePort);
	    epServer = (EndPoint)remoteEP;

            // Create a TCP/IP socket.
            Socket client = new Socket(AddressFamily.InterNetwork,
                SocketType.Stream, ProtocolType.Tcp);

            // Connect to the remote endpoint.
            client.BeginConnect(epServer, 
                new AsyncCallback(ConnectCallback), client);
            connectDone.WaitOne();

            //// Send test data to the remote device.
            //Send(client,"This is a test<EOF>");
            //sendDone.WaitOne();

            //// Receive the response from the remote device.
            //Receive(client);
            //receiveDone.WaitOne();
	    _ifInit = true;


            // Release the socket.
            //client.Shutdown(SocketShutdown.Both);
            //client.Close();
            
        } catch (Exception e) {
	     if(_initCount>3)
                {
                    _tcpError = "连接远程主机时，发生三次连接失败错误！请检查远程主机是否正常运行!重新启动本系统。";
                    return false;
                }
                _initCount++;
                _ifInit = false;

            _tcpError = e.Message ;
	    return false;
        }
    }

    private static void ConnectCallback(IAsyncResult ar) {
        try {
            // Retrieve the socket from the state object.
            Socket client = (Socket) ar.AsyncState;

            // Complete the connection.
            client.EndConnect(ar);

           

            // Signal that the connection has been made.
            connectDone.Set();
        } catch (Exception e) {
            _tcpError = e.Message ;
	    _ifInit = false;
        }
    }

    public static void Receive(Socket client) {
        try {
            // Create the state object.
            StateObject state = new StateObject();
            state.workSocket = client;

            // Begin receiving the data from the remote device.
            client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,
                new AsyncCallback(ReceiveCallback), state);
        } catch (Exception e) {
            _tcpError = e.Message ;
        }
    }

    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) {
            _tcpError = e.Message ;
        }
    }

    public static void Send(Socket client, 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.
        client.BeginSend(byteData, 0, byteData.Length, 0,
            new AsyncCallback(SendCallback), client);
    }

    private static void SendCallback(IAsyncResult ar) {
        try {
            // Retrieve the socket from the state object.
            Socket client = (Socket) ar.AsyncState;

            // Complete sending the data to the remote device.
            int bytesSent = client.EndSend(ar);
            Console.WriteLine("Sent {0} bytes to server.", bytesSent);

            // Signal that all bytes have been sent.
            sendDone.Set();
        } catch (Exception e) {
             _tcpError = e.Message ;
             

        }
    }
    
    
}
 
