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Discussion on: Angular: How to easily display loading indicators

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mhagnumdw profile image
mhagnumdw

Hi! Another question. I'm trying to understand all of your logic...

If this.isLoadingService.add receive an Observable you subscribe to it, here. And the same input Observable is returned.

And in your example, you subscribe again within your component, here: <profile-component *ngFor="let user of users | async" [user]='user'>

The observable is executed twice. Or did I miss something? Can you explain me?

Tks!!

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johncarroll profile image
John Carroll Author

The observable is executed twice

Yup. The observable is subscribed to twice. Once by the isLoadingService, and once by the async pipe in the component's template.

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mhagnumdw profile image
mhagnumdw

If it is a heavy http request you will be doing this twice, unless you use a sharereplay(1) or a ReplaySubject(1). If it is a request to create a record...
Well, what I mean is that we may have a problem here, right?

Thanks again!

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johncarroll profile image
John Carroll Author

If it is a heavy http request you will be doing this twice, unless you use a shareReplay(1) or a ReplaySubject(1)

Depends on the observable.

Well, what I mean is that we may have a problem here, right?

I can't answer that for you. I'm not familiar with your project. If you're unsure how to use observables, you can always just stick to promises (or transform observables to promises with toPromise()).

I'll note that Angular's HttpClient returns observables which complete after the request resolves. If you're using it, this isn't something you need to worry about.