Angular 中可观察到的 Promise 7+

Question

I have a problem that I can't solve.

In the ngOnInit event I observe the url parameter. This parameter corresponds to a folder in firebase-storage . That way when loading I get a list of folders and/or files inside that folder that is being informed and storing it inside listReferences variable which is of type Reference[].

Here is the code:

ngOnInit() {
  this.route.params
    .subscribe(params => {
      this.getFiles(params.ref).subscribe(
        (listReferences) => {
          this.listReferences = listReferences;
        }
      );
    }
  );
}

getFiles(folder: string) {
  return this.storage.ref('/' + folder).listAll()
  .pipe(
    map((data) => {
      return data.items;
    })
  );
}

It turns out that for each item in the listReferences array I need to access the getDownloadUrl() or getMetadata() method which are promising and I am unable to retrieve the values for each item in the array. How should I proceed in this case? How best to do this?

Basically I am following the information contained in the reference guide. https://firebase.google.com/docs/reference/js/firebase.storage.Reference

Answer 1

How about using ForkJoin as follows:

ngOnInit() {
  this.route.params
    .pipe(
      mergeMap(x => this.getFiles(x.ref)),
      mergeMap((listReferences: { getDownloadUrl: () => Promise<string> }[]) => {
        return forkJoin(listReferences.map(x => x.getDownloadUrl()))
      })
    )
    .subscribe(x =>  this.urls = x)
}