原文
http://www.cnblogs.com/Terrylee/archive/2006/10/23/Observer_Pattern.html
意图
定义对象间的一种一对多的依赖关系,当一个对象(Subject)的状态发生改变时, 所有依赖于它的对象(观察者Observer)都得到通知并被自动更新。[GOF 《设计模式》]
实例: 猫大叫一声,所有的老鼠都开始逃跑,主人被惊醒。(C#语言)
http://www.cnblogs.com/EasyLive2006/archive/2007/04/28/730805.html
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//观察者的接口
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public interface IObserver
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{
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void Response(); //观察者的响应
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}
6![](/Images/OutliningIndicators/None.gif)
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//主题的接口
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public interface ISubject
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{
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void AimAt(IObserver obs); //在主题中添加观察者,以便让这些观察者作出响应
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}
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//定义老鼠这个观察者
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public class Mouse : IObserver
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{
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private string name;
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public Mouse(string name, ISubject subj)
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{
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this.name = name;
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subj.AimAt(this);//创建老鼠时,在主题中添加这个老鼠
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}
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public void Response()
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{
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Console.WriteLine(name + " attempt to escape!");
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}
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}
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//定义主人这个观察者
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public class Master : IObserver
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{
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public Master(ISubject subj)
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{
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subj.AimAt(this);//创建主人时,在主题中添加这个老鼠
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}
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public void Response()
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{
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Console.WriteLine("Host waken!");
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}
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}
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//定义猫这个主题
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public class Cat : ISubject
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{
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private ArrayList observers;
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public Cat()
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{
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this.observers = new ArrayList();
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}
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public void AimAt(IObserver obs)
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{
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this.observers.Add(obs);
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}
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//主题动作(哭)的时候,找到它所瞄准的所有对象,并让这些对象作出响应
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public void Cry()
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{
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Console.WriteLine("Cat cryed!");
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foreach (IObserver obs in this.observers)
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{
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obs.Response();
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}
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}
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}
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//运行
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class MainClass
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{
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static void Main(string[] args)
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{
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Cat cat = new Cat(); //创建主题----猫
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Mouse mouse1 = new Mouse("mouse1", cat); //创建观察者----老鼠1,并让主题(猫)瞄准它
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Mouse mouse2 = new Mouse("mouse2", cat); //创建观察者----老鼠2,并让主题(猫)瞄准它
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Master master = new Master(cat); //创建观察者----主人,并让主题(猫)瞄准它
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cat.Cry(); //主题动作(哭)时,让瞄准的对象作出响应
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}
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}
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