Question

我在Observable中有一个GET请求。我想将它的结果发送给Observer。不幸的是，它发送了未定义的值，因为它甚至在GET执行完成之前就会与观察者进行通信 - 这就是问题所在。

 observer:Observer<any> = {
  next: objectFromObservable => { SomeActionWith() }
}


let outputToObserver;
  this.http.get(myUrl).map((programs)=>{
          const mapped = programs.json() as Program[];
      outputToObserver=mapped //here we always have desired object
          return mapped;
      })
      .subscribe(
        (res)=>{
          return res; //here we always have desired object
        }
      )
    //Here outputToObserver is undefined, so above lines are executed before mapping
      let observable:Observable<any> = Observable.create(function (obserwator) {
      observer.next(outputToObserver)

Answer 1

你可以做这样的事情

getDataFromMyUrl() {
  return this.http.get(myUrl).map((programs)=>{
          const mapped = programs.json() as Program[];
          return mapped;
      })
}

从消费方面你可以做这样的事情

var getData = getDataFromMyUrl()
                .subscribe(res => {
                     // Process the data here....
                });

Answer 2

你也可以用do来解决副作用，在这种情况下，代码可以更具可读性和线性。

let outputStream=new Subject()

this.http.get(myUrl).map((programs)=>programs.json())
.do(value=>outputStream.next(value))
.subscribe()

outputStream.subscribe()

Rxjs Observable发送未定义 - 如何避免它

2 个答案: