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观察者模式又叫做发布-订阅(Publish/Subscribe)模式。
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变化时，会通知所有观察者对象，使它们能够自动更新自己。
观察者模式所做的工作其实就是解除耦合。让耦合的双方都依赖于抽象，而不是依赖于具体。从而使得各自的变化都不会影响另一边的变化。
Demo1:
interface Subject { void Attach(Observer observer); void Detach(Observer observer); void Notify(); string SubjectState { set; get; } }
abstract class Observer { protected string name; protected Subject subject; public Observer(string name, Subject subject) { this.name = name; this.subject = subject; } public abstract void Update(); }
class StockObserver : Observer { public StockObserver(string name, Subject subject) : base(name, subject) { } public override void Update() { Console.WriteLine("{0} {1} 关闭股票行情，继续工作！", subject.SubjectState, name); } }
class Boss : Subject { private IList<Observer> observers = new List<Observer>(); private string action; public void Attach(Observer observer) { observers.Add(observer); } public void Detach(Observer observer) { observers.Remove(observer); } public void Notify() { foreach (var item in observers) { item.Update(); } } public string SubjectState { get { return action; } set { action = value; } } }
Test:
Subject boss = new Boss(); Observer p1 = new StockObserver("Jack", boss); boss.Attach(p1); boss.SubjectState = "老板回来了"; boss.Notify();
Demo2(improvement version):
interface Subject2 { //void Attach(Observer observer); //void Detach(Observer observer); void Notify(); string SubjectState { set; get; } }
class Boss2 : Subject2 { //private IList<Observer> observers = new List<Observer>(); private string action; public event Action Update; //public void Attach(Observer observer) //{ // observers.Add(observer); //} //public void Detach(Observer observer) //{ // observers.Remove(observer); //} public void Notify() { //foreach (var item in observers) //{ // item.Update(); //} Update(); } public string SubjectState { get { return action; } set { action = value; } } }
class CoderObserver { private string name; private Subject2 subject; public CoderObserver(string name, Subject2 subject) { this.name=name; this.subject=subject; } public void CoderObserverUpdate() { Console.WriteLine("{0} {1} 程序员，继续写代码！", subject.SubjectState, name); } }
class StockObserver2 { private string name; private Subject2 subject; public StockObserver2(string name, Subject2 subject) { this.name=name; this.subject=subject; } public void StockObserverUpdate() { Console.WriteLine("{0} {1} 关闭股票行情，继续工作！", subject.SubjectState, name); } }
Test:
Boss2 boss = new Boss2(); StockObserver2 ob1 = new StockObserver2("Jack", boss); CoderObserver co = new CoderObserver("Lei", boss); boss.Update += ob1.StockObserverUpdate; boss.Update += co.CoderObserverUpdate; boss.SubjectState = "老板回来了"; boss.Notify();
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原文地址：http://www.cnblogs.com/laixiancai/p/4792301.html
