一次可观察到的Firestore的angularfire2订阅

Question

I want make a firestore get items observable. But the problem is it subscribes once a time. Below is my code:

In provider:

this.allSponser = this.afs.collection<Sponsoremphasized text('sponsors').snapshotChanges().pipe(map(actions => { 
    return actions.map(a => 
    { 
        const data = a.payload.doc.data() as Sponsor; 
        data.id = a.payload.doc.id; 
        return data; 
    }); 
})); 

in signup page:

this.allSponser.subscribe(data=>{ console.log(data); }) 

printing for the first time of load if I am goingback to any other page and coming back to again signup it is not printing.

Answer 1

First of all just mentioning when you navigate away from your component it will destroyed and will recreated, so keep that in your mind, you need to subscribe to observables in ngOnInit and unsubscribe in 'ngOnDestroy'

The other point is I usually return the observalbe from my service something like this

getSoponsors() {
return this.afs.collection<Sponsoremphasizedtext>('sponsors').snapshotChanges().pipe(map(actions => { 
    return actions.map(a => 
    { 
        const data = a.payload.doc.data() as Sponsor; 
        data.id = a.payload.doc.id; 
        return data; 
    }); 
})); 
}

then in my component

isAlive: boolean = true

ngOnInit() {
  this.service.getSoponsors()
    .pipe(takeWhile(() => this.isAlive))
    .subscribe(data => ...)
}

ngOnDestroy() {
  this.isAlive = false;
}