rxjs：鏈接異步請求

Question

我是rxjs的新手，我需要調用3個異步請求，這些請求以承諾開始，並按照調用順序將重新生成的對象放入數組中。這裏是一個我已經（部分基於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); 
}); 

如何我只能發出的結果時，我有[frontOb, middleObj, endObj]？

Answer 1

由於@Eric建議您可以使用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) 
});