Gof定义

定义对象间的一种一对多的依赖关系，以便当一个对象的状态发生改变时，所有依赖于它的对象都得到通 知并自动更新

理解

观察者设计模式：当一个对象（目标对象）的状态发生改变，所有的依赖对象（观察者对象）都将得到通知。例如你在淘宝上购买了一件商品，当你付完钱后，你的淘宝帐户里会记录等待卖家发货这条信息，你的手机会收到一条短信说你手机银行里扣了钱，你的邮箱也可能会收到一封邮件。

UML图

银行取钱例子

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 观察者模式{    class Program    {        static void Main(string[] args)        {            BankAccount bank = new BankAccount();            bank.AddObserver(new Emailer());            bank.AddObserver(new Mobile());            bank.Withdraw();                        Console.ReadLine();        }    }    public class UserAccountArgs    {        public string Email { get; set; }        public string PhoneNumber { get; set; }        public UserAccountArgs(string mail, string phoneNumber)        {            Email = mail;            PhoneNumber = phoneNumber;        }    }    public interface IAccountObserver    {        void Update(UserAccountArgs args);    }    public class Emailer : IAccountObserver    {        public void Update(UserAccountArgs args)        {            Console.WriteLine("消息已发送邮件至邮箱:" + args.Email);        }    }    public class Mobile : IAccountObserver    {        public void Update(UserAccountArgs args)        {            Console.WriteLine("消息已发送短信至手机:" + args.PhoneNumber);        }    }    public class BankAccount    {        List
      
        list = new List
       
        ();        public void Withdraw()        {            Console.WriteLine("取钱任务结束");            //先写死，给UserAccountArgs初始化            UserAccountArgs args = new UserAccountArgs("ccx@126.com", "135346123113");            //给有添加到List列表里（有观察的对象，发送通知）            foreach (var item in list)            {                item.Update(args);            }        }        //添加        public void AddObserver(IAccountObserver observer)        {            list.Add(observer);        }        //移除        public void RemoveObserver(IAccountObserver observer)        {            list.Remove(observer);        }    }}
       
      

银行取钱例子，进一步，正确写法

namespace 观察者模式{    class Program    {        static void Main(string[] args)        {            BankAccount bank = new BankAccount();            bank.AddObserver(new Emailer());            bank.AddObserver(new Mobile());            bank.Withdraw();                        Console.ReadLine();        }    }    public class UserAccountArgs    {        public string Email { get; set; }        public string PhoneNumber { get; set; }        public UserAccountArgs(string mail, string phoneNumber)        {            Email = mail;            PhoneNumber = phoneNumber;        }    }    public interface IAccountObserver    {        void Update(UserAccountArgs args);    }    public class Emailer : IAccountObserver    {        public void Update(UserAccountArgs args)        {            Console.WriteLine("消息已发送邮件至邮箱:" + args.Email);        }    }    public class Mobile : IAccountObserver    {        public void Update(UserAccountArgs args)        {            Console.WriteLine("消息已发送短信至手机:" + args.PhoneNumber);        }    }    public class Subject    {        List
      
        list = new List
       
        ();        //通知        public void Notify(UserAccountArgs args)        {            foreach (var item in list)            {                item.Update(args);            }        }        //添加        public void AddObserver(IAccountObserver observer)        {            list.Add(observer);        }        //移除        public void RemoveObserver(IAccountObserver observer)        {            list.Remove(observer);        }    }    public class BankAccount : Subject    {        public void Withdraw()        {            Console.WriteLine("取钱完成！");            UserAccountArgs args = new UserAccountArgs("ccx@126.com", "1353463213");            Notify(args);        }    }}