观察者模式(Observer Pattern)：定义对象之间的一种一对多依赖关系，使得每当一个对象状态发生改变时，其相关依赖对象皆得到通知并被自动更新。观察者模式的别名包括发布-订阅（Publish/Subscribe）模式、模型-视图（Model/View）模式、源-监听器（Source/Listener）模式或从属者（Dependents）模式。
模式角色与结构：
示例代码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text; namespace CSharp.DesignPattern.ObserverPattern
{
class Program
{
static void Main(string[] args)
{
Subject subject = new ConcreteSubject(); IObserver player1 = new ConcreteObserver();
IObserver player2 = new ConcreteObserver();
IObserver player3 = new ConcreteObserver();
IObserver player4 = new ConcreteObserver(); subject.Attach(player1);
subject.Attach(player2);
subject.Attach(player3);
subject.Attach(player4); player1.BeAttacked(subject);
}
} abstract class Subject
{
protected List<IObserver> observers = new List<IObserver>(); public void Attach(IObserver observer)
{
observers.Add(observer);
} public void Detach(IObserver observer)
{
observers.Remove(observer);
} public abstract void Notify();
} class ConcreteSubject : Subject
{
public void Notify()
{
foreach (IObserver observer in observers)
{
observer.Update();
}
}
} interface IObserver
{
public void Update();
public void BeAttacked(Subject subject);
} class ConcreteObserver : IObserver
{
public void Update()
{
// To do the concrete
} public void BeAttacked(Subject subject)
{
subject.Notify();
}
}
}