自定义事件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Timers; // 计时器


namespace DemoConnection
{
    public delegate void MessageHandler(string messageText);
    public class Connection
    {
        public event MessageHandler MessageArrived; // 定义一个委托的实例
        private Timer pollTimer;

        public Connection()
        {
            pollTimer = new Timer(100);
            pollTimer.Elapsed += new ElapsedEventHandler(CheckForMessage); // 每一百毫秒执行一次
        }

        public void Connect()
        {
            pollTimer.Start();
        }

        public void Disconnect()
        {
            pollTimer.Stop();
        }

        private static Random random = new Random();
        private static int count = 0;

        private void CheckForMessage(object source,ElapsedEventArgs e)
        {
            Console.WriteLine("检测新消息.");
            if ((random.Next(9) == 0) && (MessageArrived != null))
            {
                count++;
                //触发MessageArrived事件
                MessageArrived("第"+count+"次问候您！");
            }
        }

    }

    public class Display
    {
        public void DisplayMessage(string message)
        {
            Console.WriteLine("消息来了:{0}",message);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Connection myConnection = new Connection();
            Display myDisplay = new Display();
            //将一个委托实例赋值给事件MessageArrived
            myConnection.MessageArrived += new MessageHandler(myDisplay.DisplayMessage);
            myConnection.Connect();
            Console.ReadKey();
        }
    }
}

方法论：说实话，我还不太理解这段代码。