观察者模式

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观察者模式：定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态发生改变时，会通知所有观察者对象，使它们能够自动更新自己。

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using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 观察者模式{    abstract class Subject    {        private IList<Observer> observers = new List<Observer>();        public void Add(Observer observer)        {            observers.Add(observer);        }        public void Delete(Observer observer)        {            observers.Remove(observer);        }        public void Notify()        {            foreach(Observer o in observers)            {                o.Update();            }        }    }    class ConcreteSubject : Subject    {        private string subjectState;        public string SubjectState        {            get { return subjectState; }            set { subjectState = value; }        }    }    abstract class Observer    {        public abstract void Update();    }    class ConcreteObserver : Observer    {        private string name;        private string observerState;        private ConcreteSubject subject;        public ConcreteObserver(ConcreteSubject subject,string name)        {            this.subject = subject;            this.name = name;        }        public override void Update()        {            observerState = subject.SubjectState;            Console.WriteLine("观察者{0}的状态是{1}", name, observerState);        }        public ConcreteSubject Subject        {            get { return subject; }            set { subject = value; }        }    }    class Program    {        static void Main(string[] args)        {            ConcreteSubject s = new ConcreteSubject();            s.Add(new ConcreteObserver(s, "X"));            s.Add(new ConcreteObserver(s, "Y"));            s.Add(new ConcreteObserver(s, "Z"));            s.SubjectState = "ABC";            s.Notify();            Console.Read();        }

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