event-delegate經典例子（貓叫）

上一次說過經典面試題：
＂貓叫，老鼠跑，主人驚醒＂
在觀察者模式下的實現時，提到該題還可通過＂事件－委託＂來實現.下面給出代碼（摘錄）public delegate void CryEventHandler();
    //step1　抽象事件引發者（貓）類，引發CryEventHandler類型的事件
    public abstract class Subject
    {
        public event CryEventHandler CryEvent;
        protected void FireEvent()  //不需要被子類實現
        {
            if(CryEvent!=null)
            {
                this.CryEvent();
            }
        }
    }
    //實現貓類，並通過Cry方法引發事件
    public class Cat:Subject
    {
        public void Cry()
        {
            Console.WriteLine("Cat Cryed!");
            this.FireEvent();
        }
    }
    //抽象觀察者基類
    public abstract class Observer
    {
        public Observer(Subject sub)
        {
            sub.CryEvent+=new CryEventHandler(this.Response);
        }
        public abstract void Response();
    }
    //實現老鼠／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!");
        }
    }