观察者

    public delegate void CatCall();
    public class Cat : subject
    {
        public void cry()
        {
            Console.WriteLine("猫叫了～");
            this.fireAway();
        }
    }
    public class subject
    {
        public event CatCall myEnvet;
        protected void fireAway()
        {
            if (this.myEnvet != null)
            {
                this.myEnvet();
            }
        }
    }
    public abstract class Observer
    {
        public Observer(subject sub)
        {
            sub.myEnvet += new CatCall(Response);
        }
        public abstract void Response();
    }
    public class Mouse : Observer
    {
        private string MouseName;
        public Mouse(subject sub, string name)
            : base(sub)
        {
            this.MouseName = name;
        }
        public override void Response()
        {
            Console.WriteLine(MouseName + "快跑,喵星人来了！");
        }
    }
    public class H : Observer
    {
        public H(subject sub)
            : base(sub)
        {

        }
        public override void Response()
        {
            Console.WriteLine("老鼠把我吵醒了！");
        }
    }
    public class dos
    {
        static void Main()
        {
            Cat cat = new Cat();
            Mouse mouse1 = new Mouse(cat, "Tom");
            Mouse mouse2 = new Mouse(cat, "jack");
            H h = new H(cat);
            cat.cry();
            Console.ReadKey();
        }
    }