一个UDP异步通信例子（转）

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

namespace ConsoleUdpServer
{
    class Program
    {
        static void Main(string[] args)
        {
            Socket socket = new Socket(AddressFamily.InterNetwork,
                SocketType.Dgram,
                ProtocolType.Udp);
            EndPoint localEP = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 8002);
            socket.Bind(localEP);

            //启动异步接收
            State state = new State(socket);
            socket.BeginReceiveFrom(
                state.Buffer, 0, state.Buffer.Length,
                SocketFlags.None,
                ref state.RemoteEP,
                EndReceiveFromCallback,
                state);

            Console.ReadLine();
            socket.Close();
        }

        //异步接收回调函数
        static void EndReceiveFromCallback(IAsyncResult iar)
        {
            State state = iar.AsyncState as State;
            Socket socket = state.Socket;
            try
            {
                //完成接收
                int byteRead = socket.EndReceiveFrom(iar, ref state.RemoteEP);
                //显示客户端地址和端口
                Console.WriteLine("客户端终结点：{0}", state.RemoteEP.ToString());
                //显示接收信息
                Console.WriteLine("接收数据字节数：{0}", byteRead);
                string message = Encoding.Default.GetString(state.Buffer, 0, byteRead);
                Console.WriteLine("来着客户端信息：{0}", message);
                //向客户端发送信息
                SendMeaage(socket, state.RemoteEP, "成功接收！");
            }
            catch (Exception e)
            {
                Console.WriteLine("发生异常！异常信息：");
                Console.WriteLine(e.Message);
            }
            finally
            {
                //非常重要：继续异步接收
                socket.BeginReceiveFrom(
                    state.Buffer, 0, state.Buffer.Length,
                    SocketFlags.None,
                    ref state.RemoteEP,
                    EndReceiveFromCallback,
                    state);
            }
        }

        /// <summary>
        /// 向客户端发送信息
        /// </summary>
        /// <param name="socket">本地Socket（服务器Socket）</param>
        /// <param name="remoteEndPoint">客户端终结点</param>
        /// <param name="Message">信息</param>
        static void SendMeaage(Socket socket, EndPoint remoteEndPoint, string Message)
        {
            byte[] bytes = Encoding.Default.GetBytes(Message);
            socket.SendTo(bytes, remoteEndPoint);
        }
    }

    /// <summary>
    /// 用于异步接收处理的辅助类
    /// </summary>
    class State
    {
        public State(Socket socket)
        {
            this.Buffer = new byte[1024];
            this.Socket = socket;
            this.RemoteEP = new IPEndPoint(IPAddress.Any, 0);
        }
        /// <summary>
        /// 获取本机（服务器）Socket
        /// </summary>
        public Socket Socket { get; private set; }
        /// <summary>
        /// 获取接收缓冲区
        /// </summary>
        public byte[] Buffer { get; private set; }
        /// <summary>
        /// 获取/设置客户端终结点
        /// </summary>
        public EndPoint RemoteEP;
    }
}

　　

UDP客户端

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

namespace ConsoleUdpClient
{
    class Program
    {
        static void Main(string[] args)
        {
            Socket socket = new Socket(AddressFamily.InterNetwork,
                SocketType.Dgram,
                ProtocolType.Udp);
            //客户端使用的终结点
            EndPoint localEP = new IPEndPoint(IPAddress.Any, 0);
            socket.Bind(localEP);

            //启动异步接收
            State state = new State(socket);
            socket.BeginReceiveFrom(
                state.Buffer, 0, state.Buffer.Length,
                SocketFlags.None,
                ref state.RemoteEP,
                EndReceiveFromCallback,
                state);

            //向服务器发送信息
            EndPoint remoteEP = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 8002);
            SendMeaage(socket, remoteEP, "你好，这里是客户端，收到请回复！Over~~~~");

            Console.ReadLine();
            socket.Close();
        }

        //异步接收回调函数
        static void EndReceiveFromCallback(IAsyncResult iar)
        {
            State state = iar.AsyncState as State;
            Socket socket = state.Socket;
            try
            {
                //完成接收
                int byteRead = socket.EndReceiveFrom(iar, ref state.RemoteEP);
                //显示服务器地址和端口
                Console.WriteLine("服务器终结点：{0}", state.RemoteEP.ToString());
                //显示接收信息
                Console.WriteLine("接收数据字节数：{0}", byteRead);
                string message = Encoding.Default.GetString(state.Buffer, 0, byteRead);
                Console.WriteLine("来着服务器的信息：{0}", message);
            }
            catch (Exception e)
            {
                Console.WriteLine("发生异常！异常信息：");
                Console.WriteLine(e.Message);
            }
            finally
            {
                //非常重要：继续异步接收
                socket.BeginReceiveFrom(
                    state.Buffer, 0, state.Buffer.Length,
                    SocketFlags.None,
                    ref state.RemoteEP,
                    EndReceiveFromCallback,
                    state);
            }
        }

        /// <summary>
        /// 向服务器发送信息
        /// </summary>
        /// <param name="socket">本地Socket</param>
        /// <param name="remoteEndPoint">服务器终结点</param>
        /// <param name="Message">信息</param>
        static void SendMeaage(Socket socket, EndPoint remoteEndPoint, string Message)
        {
            byte[] bytes = Encoding.Default.GetBytes(Message);
            socket.SendTo(bytes, remoteEndPoint);
        }
    }


    /// <summary>
    /// 用于异步接收处理的辅助类
    /// </summary>
    class State
    {
        public State(Socket socket)
        {
            this.Buffer = new byte[1024];
            this.Socket = socket;
            this.RemoteEP = new IPEndPoint(IPAddress.Any, 0);
        }
        /// <summary>
        /// 获取本机Socket
        /// </summary>
        public Socket Socket { get; private set; }
        /// <summary>
        /// 获取接收缓冲区
        /// </summary>
        public byte[] Buffer { get; private set; }
        /// <summary>
        /// 获取/设置客户端终结点
        /// </summary>
        public EndPoint RemoteEP;
    }
}