rxjs：链接异步请求

Question

我是 rxjs 的新手，我需要调用 3 个异步请求，这些请求以 promises 开始，并将返回的对象按照调用顺序放入数组中。这是我的（部分基于）：

let observeFront = Observable.fromPromise(this.requestAsync(frontSlice, "front"));
let observeMiddle = Observable.fromPromise(this.requestAsync(midSlice, "middle"));
let observeEnd = Observable.fromPromise(this.requestAsync(endSlice, "end"));

let observeCombined = Observable.concat(observeFront, observeMiddle, observeEnd);

observeCombined.subscribe(data => {
  // this logs only one object - need all 3 in proper order
  console.log(data);
  this.resultsEmitter.emit(data)
});

observeFront.subscribe(response => {
  // logs the correct object
  console.log("front result:", response);
});

observeMiddle.subscribe(response => {
  // correct
  console.log("middle result:", response);
});

observeEnd.subscribe(response => {
  // correct
  console.log("end result:", response);
});

如何仅在我有 [frontOb, middleObj, endObj] 时发出结果？

Answer 1

正如@Eric 建议的那样，您可以使用 forkJoin() 而不是 concat():

let observeFront = Observable.fromPromise(this.requestAsync(frontSlice, "front"));
let observeMiddle = Observable.fromPromise(this.requestAsync(midSlice, "middle"));
let observeEnd = Observable.fromPromise(this.requestAsync(endSlice, "end"));

let observeJoined = Observable.forkJoin(observeFront, observeMiddle, observeEnd);

observeJoined.subscribe(data => {
  console.log(data); // => [frontOb, middleObj, endObj]
  this.resultsEmitter.emit(data)
});

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