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，这些请求以承诺开始，并按照调用顺序将重新生成的对象放入数组中。这里是一个我已经（部分基于this question）：

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); 
}); 

如何我只能发出的结果时，我有[frontOb, middleObj, endObj]？

Answer 1

由于@Eric建议您可以使用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) 
});