英文:
Why forkJoin does not emit value?
问题
这里有一个加载主题，触发了两个流。在这些流合并成一个之后：
this.sourceWithImage$ = this.load$.pipe(
switchMap(() =>
of(1).pipe(
delay(3000),
map(() => new Date().getMilliseconds())
)
)
);
this.sourceWithFields$ = this.load$.pipe(
switchMap(() =>
of(2).pipe(
delay(2000),
map(() => new Date().getMilliseconds())
)
)
);
this.sourceData$ = this.load$.pipe(
switchMap(() => forkJoin([this.sourceWithImage$, this.sourceWithFields$]))
);
this.sourceData$.subscribe((e) => console.log(e));
为什么 forkJoin 没有发出值？我需要并行加载两个流。
英文:
There is a load$ subject that triggers two stream. After these streams forked into one:
this.sourceWithImage$ = this.load$.pipe(
switchMap(() =>
of(1).pipe(
delay(3000),
map(() => new Date().getMilliseconds())
)
)
);
this.sourceWithFields$ = this.load$.pipe(
switchMap(() =>
of(2).pipe(
delay(2000),
map(() => new Date().getMilliseconds())
)
)
);
this.sourceData$ = this.load$.pipe(
switchMap(() => forkJoin([this.sourceWithImage$, this.sourceWithFields$]))
);
this.sourceData$.subscribe((e) => console.log(e));
Stackblitz link
Why forkJoin does not emit value?
I need to load two streams in parallel
答案1
得分: 1
forkJoin只有在所有输入都完成后才能发出值。
等待Observables完成，然后组合它们最后发出的值；如果传递一个空数组，立即完成
因此，您可能想要使用 take(1) 或更改您的逻辑，像这样
Stackblitz示例
const load$ = new Subject();
const sourceWithImage$ = of(1).pipe(
delay(3000),
map(() => new Date().getMilliseconds())
);
const sourceWithFields$ = of(2).pipe(
delay(2000),
map(() => new Date().getMilliseconds())
);
const sourceData$ = load$.pipe(
switchMap(() => forkJoin([sourceWithImage$, sourceWithFields$]))
);
sourceData$.subscribe({
next: (v) => console.log(v),
error: (e) => console.log(e),
});
load$.next(1);
英文:
forkJoin can only emit a value when all inputs have finished.
ForkJoin docs
> Wait for Observables to complete and then combine last values they emitted; complete immediately if an empty array is passed
So you may want to use take(1) or change your logic, like this
Stackblitz example
const load$ = new Subject();
const sourceWithImage$ = of(1).pipe(
delay(3000),
map(() => new Date().getMilliseconds())
);
const sourceWithFields$ = of(2).pipe(
delay(2000),
map(() => new Date().getMilliseconds())
);
const sourceData$ = load$.pipe(
switchMap(() => forkJoin([sourceWithImage$, sourceWithFields$]))
);
sourceData$.subscribe({
next: (v) => console.log(v),
error: (e) => console.log(e),
});
load$.next(1);
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