UDPSocket.cs

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

namespace MiLightYL5
{
    public class UDPSocket
    {
        private Socket _socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        private const int bufSize = 64;
        private State state = new State();
        private EndPoint epFrom = new IPEndPoint(IPAddress.Any, 0);
        private AsyncCallback recv = null;

        public class State
        {
            public byte[] buffer = new byte[bufSize];
        }

        public void Server(string address, int port)
        {
            _socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.ReuseAddress, true);
            _socket.Bind(new IPEndPoint(IPAddress.Parse(address), port));
            Receive();            
        }

        public void Client(string address, int port)
        {
            _socket.Connect(IPAddress.Parse(address), port);
            Receive();            
        }

        public void Disconnect()
        {
            if(_socket.Connected)
                _socket.Disconnect(true);
        }

        public void Send(byte[] data)
        {            
            _socket.BeginSend(data, 0, data.Length, SocketFlags.None, (ar) =>
            {
                State so = (State)ar.AsyncState;
                int bytes = _socket.EndSend(ar);
            }, state);
        }

        public byte[] Receive()
        {            
            _socket.BeginReceiveFrom(state.buffer, 0, bufSize, SocketFlags.None, ref epFrom, recv = (ar) =>
            {
                State so = (State)ar.AsyncState;
                int bytes = _socket.EndReceiveFrom(ar, ref epFrom);
                _socket.BeginReceiveFrom(so.buffer, 0, bufSize, SocketFlags.None, ref epFrom, recv, so);
                //Console.WriteLine("RECV: {0}: {1}, {2}", epFrom.ToString(), bytes, Encoding.ASCII.GetString(so.buffer, 0, bytes));
            }, state);
            return state.buffer;
        }   

    }
}