基于之前的可观察对象切换可观察对象

Question

我有一个 observable A，它 returns 布尔值 observable 并且基于 observable A 的值，我需要调用 wither observable B 或 C

observableA = of(true);

observableB(): observable<string> {
}

observableC(): observable<string> {
}

function value () {
   return observableA.pipe(map(value => {
     if(value) {
      return observableB();
     } else {
      return observableC();
    }

}))
}

Answer 1

为了根据真实值区分调用哪个可观察对象。示例如下

case => true => 多项乘以 10
case => false => multiple item by 20


import { of, Subject } from "rxjs";
import { map } from "rxjs/operators";

const observableInvokeOnTruthy$ = of(1, 2, 3, 4, 5);
const observableInvokeOnFalsy$ = of(1, 2, 3, 4, 5);
const emitValuesSubject$ = new Subject();

emitValuesSubject$.subscribe(response => {
  if (response) {
    console.log("TRUTHY VALUE:");
    observableInvokeOnTruthy$
      .pipe(
        map(item => {
          return item * 10;
        })
      )
      .subscribe(result => {
        console.log(result);
      });
  } else {
    console.log("FALSY VALUE:");
    observableInvokeOnFalsy$
      .pipe(
        map(item => {
          return item * 20;
        })
      )
      .subscribe(result => {
        console.log(result);
      });
  }
});

emitValuesSubject$.next(false);
emitValuesSubject$.next(true);

Answer 2

您可以使用 switchMap 运算符代替 map:

function value () {
   return observableA.pipe(switchMap(value => {
     if(value) {
      return observableB();
     } else {
      return observableC();
    }

}))

基于之前的可观察对象切换可观察对象

switch observable based on previous observable

observable

angular-observable