我如何迭代返回rxjs observables的函数

问题描述

我想遍历一系列异步函数，并在返回false时结束迭代。 我是rxjs的新手，无法使用以下用例。我觉得我不了解一些基本知识。有人可以向我指出吗？

function validateA(): Observable<any> {
  // do stuff.
  return of({ id: "A",result: true }); // hardcoding result for Now
}

function validateB(): Observable<any> {
  // do stuff
  return of({ id: "B",result: true }); // hardcoding result for Now
}

function validateC(): Observable<any> {
  // do stuff
  return of({ id: "C",result: false });// hardcoding result for Now
}

from([validateA,validateB,validateC])
  .pipe(
    map(data => data()),takeWhile(data => !!data.result)
  )
  .subscribe(data => console.log(`${data.id} passed!`));

https://stackblitz.com/edit/typescript-ub9c5r?file=index.ts&devtoolsheight=100

解决方法

以下似乎可以解决问题，并懒惰地调用函数：

https://stackblitz.com/edit/typescript-9ystxv?file=index.ts

import {  from,Observable,of } from "rxjs";
import {  concatAll,find,map } from "rxjs/operators";

function validateA() {
  console.log('validateA');
  return of({ id: "A",result: false });
}

function validateB() {
  console.log('validateB');
  return of({ id: "B",result: true });
}

function validateC() {
  console.log('validateC');
  return of({ id: "C",result: false });
}

from([validateA,validateB,validateC])
  .pipe(
    map(validate => validate()),concatAll(),find(data => data.result)
  )
  .subscribe(data => console.log(`${data.id} passed!`));

,

我要说的是，您逻辑的核心是正确的。缺少的是rxJs的特殊之处。

解决方案可能是这样的。注释中有细微差别的解释。

// start from an array of functions and turn it into a stream using RxJs from function
from([validateA,validateC])
  .pipe(
    // now execute each function sequentially,one after the other,via concatMap
    // operator. This operator calls each function and each function returns an Observable
    // concatMap ensures that the functions are called sequentially and also that the returned Observable (because each function returns an Observable)
    // is "flattened" in the result stream. In other words,you execute each function one at the time
    // and return the value emitted by the Observable returned by that function
    // until that Observable completes. Considering that you use the "of" function to
    // create the Observable which is returned by each function,such Observable emits just one value and then completes.
    concatMap(func => func()),// now you have a stream of values notified by the Observables returned by the functions
    // and you terminate as soon as a flase is received
    takeWhile(data => !!data.result)
  )
  .subscribe(data => console.log(`${data.id} passed!`));