在两个单独的成功 http 请求后触发回调

Question

我的应用程序的根组件在初始化时从我的服务中调用两个异步函数来获取数据。我想知道它们都完成后如何调用一个函数。我正在使用 angular 2.0.0-alpha.44 和 typescript 1.7.3

import {Component, OnInit} from 'angular2/angular2';

import {ServiceA} from './services/A';
import {ServiceB} from './services/B';


@Component({
  selector: 'app',
  template: `<h1>Hello</h1>`
})
export class App {
  constructor(
    public serviceA: ServiceA,
    public serviceB: ServiceB
  ) { }

  onInit() {

    // How to run a callback, after 
    // both getDataA and getDataB are completed?
    // I am looing for something similar to jQuery $.when()
    this.serviceA.getDataA();
    this.serviceB.getDataB();
  }
}

serviceA.getDataA 和 serviceA.getDataB 是简单的 http get 函数：

// Part of serviceA
getDataA() {
  this.http.get('./some/data.json')
    .map(res => res.json())
    .subscribe(
      data => {
        // save res to variable
        this.data = data;
      },
      error => console.log(error),
      // The callback here will run after only one 
      // function is completed. Not what I am looking for.
      () => console.log('Completed')
    );
}

Answer 1

一个简单的仍然并行的解决方案是这样的：

let serviceStatus = { aDone: false, bDone: false };

 let getDataA = (callback: () => void) => {
     // do whatver.. 
     callback();
 }

 let getDataB = (callback: () => void) => {
     // do whatver.. 
     callback();
 }

 let bothDone = () => { console.log("A and B are done!");

 let checkServiceStatus = () => {

     if ((serviceStatus.aDone && serviceStatus.bDone) == true)
        bothDone();
 }

 getDataA(() => { 
     serviceStatus.aDone = true;
     checkServiceStatus(); 
});

getDataA(() => { 
     serviceStatus.bDone = true;
     checkServiceStatus(); 
});

我个人使用RxJS 让我摆脱这种棘手的情况，可能值得一看。

编辑：

鉴于实际使用 RxJS 的反馈：

let observable1: Rx.Observable<something>;
let observable2: Rx.Observable<something>;

let combinedObservable = Rx.Observable
    .zip(
        observable1.take(1), 
        observable2.take(1),
        (result1, result2) => {
            // you can return whatever you want here
            return { result1, result2 };
        });

combinedObservable
    .subscribe(combinedResult => {
        // here both observable1 and observable2 will be done.
    });

此示例将并行运行两个可观察对象，并在它们都完成后将结果合并为一个结果。

Answer 2

您可以在函数定义中传递 getDataA 和 getDataB 回调，然后按顺序调用您想要的任何内容：

function getDataA(callback) {
     // do some stuff
     callback && callback();
}

function getDataB(callback) {
     // do some stuff
     callback && callback();
}

function toCallAfterBoth() {
    // do some stuff
}
getDataA(getDataB(toCallAfterBoth));

Answer 3

你可以嵌套你的函数调用。

EG：

function getDataA (callback) {
    var dataA = {test:"Hello Data A"};
    callback && callback(dataA);
}

function getDataB (callback) {
    var dataB = {test:"Hello Data B"};
    callback && callback(dataB);
}

getDataA(function (dataA) {
    getDataB(function (dataB) {
        console.log("Both functions are complete and you have data:");
        console.log(dataA);
        console.log(dataB);
    });
});