How to clean/clear cache of a SubjectReplay instance in rxjs?

问题

I have a SubjectReplay and I would like to reset it to no cache values so after this reset the next subscriber doesn't get the history?

Example

new subject replay
subject.next(1)
reset subject <- this question
subject.subscribe() // should NOT receive 1

how can I do this? I need the subject to be the same instance.

回答1:

You may look at using a combination of special values and filter operator to get something close to what you are trying to achieve.

Let's make a simple case.

You want to replay just the last value and null is the special value representing the reset. The code would be

const rs = new ReplaySubject<any>(1); // replay the last value
const rsObs = rs.asObservable().pipe(filter(d => d !== null));
rs.next(1);
rs.next(2);

setTimeout(() => {
    console.log('first subscription');
    rsObs.subscribe(console.log)  // logs 2 on the console
}, 10);


setTimeout(() => {
    rs.next(null);
}, 20);


setTimeout(() => {
    console.log('second subscription');
    rsObs.subscribe(console.log)  // nothing is logged
}, 30);

回答2:

The best way that comes to my mind with your requirement

I need the subject to be the same instance

would be to have the following observables:

// This is your input
const source$: Observable<T>;

const proxy$ = new ReplaySubject<T>(n);
const reset$ = new BehaviorSubject<number>(0);

Now it's important that we hook up the following before you emit on source$:

source$.pipe(timestamp()).subscribe(proxy$);

Then, finally, you can expose your data like this:

const data$ = proxy$.pipe(
  withLatestFrom(reset$),
  filter(([timedItem, resetTimestamp]) => timedItem.timestamp > resetTimestamp),
  map(([timedItem]) => timedItem.value),
);

You can now use reset$.next(+new Date()) to trigger the reset.

If you can make sure to provide timestamped values to source$, you can skip the proxy$.

来源：https://stackoverflow.com/questions/50996348/how-to-clean-clear-cache-of-a-subjectreplay-instance-in-rxjs

标签

stream

rxjs