eventdelegate经典例子（猫叫）

上一次说过经典面试题：
＂猫叫，老鼠跑，主人惊醒＂
在观察者模式下的实现时，提到该题还可通过＂事件－委托＂来实现.下面给出代码（摘录）

public delegate void CryEventHandler();
    //step1　抽象事件引发者（猫）类，引发CryEventHandler类型的事件
    public abstract class Subject
    {
        public event CryEventHandler CryEvent;
        protected void FireEvent()  //不需要被子类实现
        {
            if(CryEvent!=null)
            {
                this.CryEvent();
            }
        }
    }
    //实现猫类，并通过Cry方法引发事件
    public class Cat:Subject
    {
        public void Cry()
        {
            Console.WriteLine("Cat Cryed!");
            this.FireEvent();
        }
    }
    //抽象观察者基类
    public abstract class Observer
    {
        public Observer(Subject sub)
        {
            sub.CryEvent+=new CryEventHandler(this.Response);
        }
        public abstract void Response();
    }
    //实现老鼠／主人
    public class Mouse:Observer
    {
        private string name;
        public Mouse(string name,Subject sub):base(sub)
        {
            this.name=name;
        }
        public override void  Response()
        {
            Console.WriteLine("Cat Cryed!"+name+" Run!");
        }
    }
     public class Master:Observer
    {
        private string name;
        public Master(string name,Subject sub):base(sub)
        {
            this.name=name;
        }
        public override void  Response()
        {
            Console.WriteLine("Cat Cryed!"+name+" WeakUP!");
        }
    }