观察者模式（Observer）

/*
 * 网上商店中如果商品（product）在名称（name）、价格（price）等
 * 方面有变化，系统能自动通知会员，将是网上商店区别传统商店的一
 * 大特色。应用外观模式，用C#控制台应用程序改进设计。
 */
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Observer
{
    //观察者-会员类
    class Vip
    {
        private string name;
        private string rcv_msg;
        private ShopSystem shopsystem;

        public Vip(ShopSystem shopsystem, string name)
        {
            this.shopsystem = shopsystem;
            this.name = name;
        }
        public void RcvMsg()
        {
            rcv_msg = shopsystem.SndMsg;
            Console.WriteLine("尊敬的{0}，{1}，预购从速哦~亲~",name,rcv_msg);
        }
    }
    //通知者-系统类
    class ShopSystem
    {
        private string snd_msg;
        private IList<Vip> vips = new List<Vip>();
        public string SndMsg
        {
            get { return snd_msg; }
            set { snd_msg = value; }
        }
        public void Attach(Vip vip)
        {
            vips.Add(vip);
        }
        public void Detach(Vip vip)
        {
            vips.Remove(vip);
        }
        public void Notify()
        {
            foreach (Vip vip in vips)
            {
                vip.RcvMsg();
            }
        }
    }
    //Client-商品类
    class Product
    {
        private string name;
        private string price;
        public Product(string name, string price)
        {
            this.name = name;
            this.price = price;
        }
        public void SetName(ShopSystem shopsystem,string name)
        {
            shopsystem.SndMsg=("【"+this.name+"】改名为【"+name+"】");
            shopsystem.Notify();
            this.name = name;
        }
        public void SetPrice(ShopSystem shopsystem,string price)
        {
            shopsystem.SndMsg = ("【" + name + "】价格由【" + this.price + "】调整为【" + price + "】");
            shopsystem.Notify();
            this.price = price;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Product pro1 = new Product("北京方便面","0.7￥");
            Product pro2 = new Product("武汉热干面","2.0￥");
            ShopSystem shopsystem = new ShopSystem();
            shopsystem.Attach(new Vip(shopsystem, "魏艾皮"));
            shopsystem.Attach(new Vip(shopsystem, "卫蔼霹"));

            pro1.SetName(shopsystem,"超级北京方便面");
            pro2.SetName(shopsystem,"无敌武汉热干面");
            pro1.SetPrice(shopsystem, "0.5￥");
            pro1.SetPrice(shopsystem, "1.5￥");
        }
    }
}