using System;
using System.Collections.Generic;
using System.Threading;namespace RefactoringGuru.DesignPatterns.Observer.Conceptual
{// Observer观察者 也可以叫做订阅者 subscriberspublic interface IObserver{// Receive update from subject// 接收来自主题的更新void Update(ISubject subject);}// 拥有一些值得关注的状态的对象通常被称为目标， 由于它要将自身的状态改变通知给其他对象， 我们也将其称为发布者 （publisher）。public interface ISubject{// Attach an observer to the subject.// 加一个观察者。void Attach(IObserver observer);// Detach an observer from the subject.// 删一个观察者。void Detach(IObserver observer);// Notify all observers about an event.// 通知所有观察者 某一事件 void Notify();}// The Subject owns some important state and notifies observers when the// state changes.// 主题拥有一些重要的状态，并在状态发生变化时通知观察者。// 也可以叫发布者 Publisherpublic class Subject : ISubject{// For the sake of simplicity, the Subject's state, essential to all// subscribers, is stored in this variable.// 为了简便起见，主题的状态，对所有订阅者都至关重要的，存储在这个变量中。public int State { get; set; } = -0;// List of subscribers. In real life, the list of subscribers can be// stored more comprehensively (categorized by event type, etc.).// 订阅者列表。在现实生活中，订阅者列表可以更全面地存储（按事件类型等分类）。private List<IObserver> _observers = new List<IObserver>();// The subscription management methods.public void Attach(IObserver observer){Console.WriteLine("Subject: Attached an observer.");this._observers.Add(observer);}public void Detach(IObserver observer){this._observers.Remove(observer);Console.WriteLine("Subject: Detached an observer.");}// Trigger an update in each subscriber.// 在每个订阅者中触发更新public void Notify(){Console.WriteLine("Subject: Notifying observers...");foreach (var observer in _observers){observer.Update(this);}}// Usually, the subscription logic is only a fraction of what a Subject// can really do. Subjects commonly hold some important business logic,// that triggers a notification method whenever something important is// about to happen (or after it).// 通常，订阅逻辑只是主题真正能做的一小部分。主题通常包含一些重要的业务逻辑，每当重要的事情即将发生（或之后）时，就会触发通知方法。public void SomeBusinessLogic(){Console.WriteLine("\nSubject: I'm doing something important.");this.State = new Random().Next(0, 10);Thread.Sleep(15);Console.WriteLine("Subject: My state has just changed to: " + this.State);this.Notify();}}// Concrete Observers react to the updates issued by the Subject they had// been attached to.class ConcreteObserverA : IObserver{public void Update(ISubject subject){if ((subject as Subject).State < 3){Console.WriteLine("ConcreteObserverA: Reacted to the event.");}}}class ConcreteObserverB : IObserver{public void Update(ISubject subject){if ((subject as Subject).State == 0 || (subject as Subject).State >= 2){Console.WriteLine("ConcreteObserverB: Reacted to the event.");}}}class Program{static void Main(string[] args){// The client code.var subject = new Subject();var observerA = new ConcreteObserverA();subject.Attach(observerA);var observerB = new ConcreteObserverB();subject.Attach(observerB);subject.SomeBusinessLogic();subject.SomeBusinessLogic();subject.Detach(observerB);subject.SomeBusinessLogic();}}
}

输出：

Subject: Attached an observer.
Subject: Attached an observer.Subject: I'm doing something important.
Subject: My state has just changed to: 2
Subject: Notifying observers...
ConcreteObserverA: Reacted to the event.
ConcreteObserverB: Reacted to the event.Subject: I'm doing something important.
Subject: My state has just changed to: 1
Subject: Notifying observers...
ConcreteObserverA: Reacted to the event.
Subject: Detached an observer.Subject: I'm doing something important.
Subject: My state has just changed to: 5
Subject: Notifying observers...

 原文链接：

C# 观察者模式讲解和代码示例

仅供学习参考，如有侵权联系我删除