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();        }    }

来源：http://www.cnblogs.com/smailxiaobai/archive/2012/03/07/2383486.html