设计模式在 TypeScript 中的应用 - 观察者模式

// 发布类
class Subject {
  // 缓存列表，用以存放回调函数，以便通知订阅者
  private observers: Observer[] = new Array<Observer>()
  private state: number

  // 新增订阅者
  public subscribe (observer: Observer): void {
    this.observers.push(observer)
  }

  // 改变状态，通知订阅者
  public setState(state: number): void {
    console.log(`Warning: State changed: ${state}`)
    this.state = state
    this.publish()
  }

  // 获取状态
  public getState(): number {
    return this.state
  }

  // 发布事件
  public publish (): void {
    for (let observer of this.observers) {
      observer.update()
    }
  }

  // 取消订阅
  public unsubscribe (observer?: Observer): void {
    // 如果没传参数，则清空订阅者
    if (!observer) {
      this.observers = new Array<Observer>()
    } else {
      this.observers.splice(this.observers.indexOf(observer), 1)
    }
  }
}

// 订阅者抽象类
abstract class Observer {
  // 订阅的内容
  protected subject: Subject

  // 订阅更新
  public abstract update (): void
}

class AObserver extends Observer {
  // 构造方法里订阅
  public constructor (subject: Subject) {
    super()
    this.subject = subject
    this.subject.subscribe(this)
  }

  public update() {
    console.log(`AObserver: ${this.subject.getState()}`)
  }
}

class BObserver extends Observer {
  // 构造方法里订阅
  public constructor (subject: Subject) {
    super()
    this.subject = subject
    this.subject.subscribe(this)
  }

  public update() {
    console.log(`BObserver: ${this.subject.getState()}`)
  }
}

const subject = new Subject()

const aObserver = new AObserver(subject)
const bObserver = new BObserver(subject)

console.log('========')
console.log('State change: 100')
subject.setState(100)
console.log('========')

console.log('=========')
console.log('aObserver 取消订阅')
subject.unsubscribe(aObserver)
console.log('State change: 150')
subject.setState(150)
console.log('=========')

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