观察者模式（猫大叫一声，主人惊醒，老鼠跑）

    public delegate void SubEventHandle();
    public abstract class Subject
    {
       
        public event SubEventHandle SubEvent;
        public void OnSub() 
        {
            if (SubEvent != null)
                SubEvent();
        }
    }

    public abstract class Observer 
    {
        public Observer(Subject sub) 
        {
            sub.SubEvent += new SubEventHandle(Response);
        }
        protected abstract void Response();
    }

    public class Mouse : Observer 
    {
        public Mouse(Subject sub):base(sub)
        {
            
        }
        public override void Response()
        {
            
        }
    }

    public class Master : Observer 
    {
        public Master(Subject sub) : base(sub) 
        {
        }

        protected override void Response()
        {
            
        }
    }

    public class Cat : Subject
    {
        private List<Observer> observers;
        public Cat()
        {
            observers = new List<Observer>();
        }

        public void Cry()
        {
            base.OnSub();
        }
    }