msdn 上的关于delegate和event的一个例子，理解后加点评论

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace EventSamle
{
        public class AlarmEventArgs : System.EventArgs//事件参数
        {
            private  bool _snoozPresed;//懒惰键
            private int _nrings;//响了几次

            public bool SnoozPressed
            {
                get { return _snoozPresed; }
                set { _snoozPresed = value; }
            }

            public int NumRings
            {
                get { return _nrings; }
                set { _nrings = value; }
            }

            public string AlarmText//提醒
            {
                get
                {
                    if (SnoozPressed)
                        return ("Wake up!!! snooze time is over.");
                    else
                        return ("Wake up!!!");
                }
            }

            public AlarmEventArgs(bool snooz, int nrings)
            {
                this._snoozPresed = snooz;
                this._nrings = nrings;
            }

        }

        public delegate void AlarmEventHander(object sender, AlarmEventArgs e);//1.声明委托事件处理函数，其实是个类

        public class AlarmClock//产生事件的类
        {
            private bool _snoozPressed = false;
            private int _nrings = 0;
            private bool _stop = false;

            public bool Stop//是否停止。事件类的域，这个例子中事件处理函数会反馈修改这个域的值
            {
                get { return _stop; }
                set { _stop = value; }
            }
            public bool SnoozPressed//是否懒惰。事件类的域，这个例子中事件处理函数会反馈修改这个域的值
            {
                get { return _snoozPressed; }
                set { _snoozPressed = value; }
            }

            public event AlarmEventHander Alarm;//2.声明一个事件，或叫做产生一个委托事件处理函数的实例
            protected virtual void OnAlarm(AlarmEventArgs e)//3.触发事件的函数，protected
            {
                if (Alarm != null)//一定要加！
                {
                    Alarm(this, e);
                }
            }

            public void Start()//调用这个函数后开始触发事件，传入参数
            {
                for (; ; )
                {
                    _nrings++;
                    if (Stop)
                        break;
                    else if (SnoozPressed)
                    {
                        System.Threading.Thread.Sleep(1000);
                        AlarmEventArgs e = new AlarmEventArgs(SnoozPressed, _nrings);
                        OnAlarm(e);
                    }
                    else
                    {
                        System.Threading.Thread.Sleep(300);
                        AlarmEventArgs e = new AlarmEventArgs(SnoozPressed, _nrings);
                        OnAlarm(e);
                    }
                }
            }
        }

        public class WakeUp//处理事件的类
        {
            public void RingRang(object sender, AlarmEventArgs e)//4.处理事件的函数，同delegate签名一样
            {
                Console.WriteLine(e.AlarmText+"\n");
                if(!e.SnoozPressed)
                {
                    Console.WriteLine(" Let alarm ring? Enter Y");
                    Console.WriteLine(" Stop Alarm? Enter Q");
                     Console.WriteLine(" Press Snooze? Enter N");
                    string input = Console.ReadLine();
                    if(input.Equals("Y")||input.Equals("y")) return;
                    else  if(input.Equals("Q")||input.Equals("q")) 
                    {

                        ((AlarmClock)sender).Stop = true;//这个例子中可以向发送者反馈信息
                        return;
                    }
                    else
                    {
                        ((AlarmClock)sender).SnoozPressed = true;
                        return;
                    }
                }
                else 
                {
                    Console.WriteLine(" Let alarm ring? Enter Y");
                    Console.WriteLine(" Stop Alarm? Enter Q");
                    string input = Console.ReadLine();
                    if(input.Equals("Y")||input.Equals("y")) return;
                    if(input.Equals("Q")||input.Equals("q")) 
                    {
                        ((AlarmClock)sender).Stop = true;
                        return;
                    }
                }

            }
        }
       
   public class AlarmDriver//测试类
   {  
      public static void Main (string[] args)
      {  
         // Instantiates the event receiver.
         WakeUp w= new WakeUp();
                  
         // Instantiates the event source.
         AlarmClock clock = new AlarmClock();

         // Wires the AlarmRang method to the Alarm event.
         clock.Alarm += new AlarmEventHander(w.RingRang);//把事件处理函数注册到事件处理队列中

         clock.Start();
      }
   }   

}