Angular 2 服务调用未从 Angularfire 2 流中定义？

Question

我有一个操作，我使用 angularfire2 从我的 firebase 中获取一些数据，映射它并对数据进行一些更新/检查，然后我想再次保存它，但我遇到了一个奇怪的问题，它告诉我' this.fs.getRiders' 未定义？但我正在使用服务来创建流，我不太确定这里发生了什么。

这里有一些代码

 @Injectable()
      export class RoundService {

    public currentRound:FirebaseListObservable<any>;

constructor(private af: AngularFire, private as:AuthService, private fs:FirebaseService) { }

pullCurrentRound(serieUid:string){  

  return this.af.database.object(`series/${serieUid}/currentRound`)
    .flatMap((res)=>{
      return this.af.database.object(`rounds/${res.$value}`)
        .map((res)=>res)
        .do(this.roundUpdates)
        .do(this.saveRound)
    })
}

saveRound(round){

    this.fs.getRiders.update(round.uid,round)
      .then(snap=>{
        console.log(snap)
      })
}

还有错误

 Uncaught TypeError: Cannot read property 'getRiders' of undefined
at SafeSubscriber.RoundService.saveRound [as _next] (round.service.ts:57)
at SafeSubscriber.__tryOrSetError (Subscriber.js:232)
at SafeSubscriber.next (Subscriber.js:174)
at Subscriber._next (Subscriber.js:125)
at Subscriber.next (Subscriber.js:89)
at DoSubscriber._next (do.js:82)
at DoSubscriber.Subscriber.next (Subscriber.js:89)
at DoSubscriber._next (do.js:87)
at DoSubscriber.Subscriber.next (Subscriber.js:89)
at MapSubscriber._next (map.js:83)

有人有想法吗？

Answer 1

this 没有指向您期望的位置

pullCurrentRound(serieUid:string){  

  return this.af.database.object(`series/${serieUid}/currentRound`)
    .flatMap((res)=>{
      return this.af.database.object(`rounds/${res.$value}`)
        .map((res)=>res)
        .do(this.roundUpdates.bind(this)) // <<< changed
        .do(this.saveRound.bind(this) // <<< changed
    })
}

随着这一变化this 一直指向roundUpdates 和saveRound 中的当前类实例

另一种方法是使用箭头函数，但在具体情况下它们不太方便

pullCurrentRound(serieUid:string){  

  return this.af.database.object(`series/${serieUid}/currentRound`)
    .flatMap((res)=>{
      return this.af.database.object(`rounds/${res.$value}`)
        .map((res)=>res)
        .do(x => roundUpdates(x)) // <<< changed
        .do(round => this.saveRound(round) // <<< changed
    })
}