Reorganizing Firebase data in Ionic 2

I am currently working on an exciting project to develop an Ionic notes application, where users can easily rearrange items in the list using the reorderArray() function. However, I encountered an issue with Firebase resulting in an error message related to this.notesList.

Argument of type 'Observable' is not assignable to parameter of type 'any[]'. Property 'length' is missing in type 'Observable'.

I am seeking guidance on how to integrate Firebase correctly into my project. Your assistance would be highly appreciated. Below is a snippet of my code:

HTML:

<div *ngIf="editmode">
  <ion-list reorder="true" (ionItemReoder)="reorderItem($event)">

    <ion-item *ngFor="let note of notesList | async">
      <ion-checkbox (ionChange)="addToTrash(note.id)"></ion-checkbox>

      <ion-label>
        <h1>{{ note.name }}</h1>
        <span>{{ note.note_date | date: 'shortDate' }}</span>
        <span>{{ note.text }}</span>
        <span>{{ (notesList | async)?.length }}</span>
      </ion-label>

    </ion-item>

  </ion-list>
</div>

Typescript:

export class NotesPage {

  notesList: Observable<any>;
  editmode: boolean = false;
  trash = [];

  constructor(
    public navCtrl: NavController, 
    public navParams: NavParams,
    public database: AngularFireDatabase,
    public loadingCtrl: LoadingController,
    public alertCtrl: AlertController
  ) {
    this.loadNotes();
  }

  loadNotes() {
    const loader = this.loadingCtrl.create();
    loader.present().then( () => {
      this.notesList = this.database.list('/notes').valueChanges();
      loader.dismiss();
    })
  }

  reorderItem( indexes ) {
    this.notesList = reorderArray(this.notesList, indexes);
  }

}

Answer №1

this.notesList is considered an Observable in this scenario. The function reorderItems specifically works with items that are similar to arrays, so the following code snippet should help resolve the issue.

notesList: any[];

[...]

loadNotes() {
  const loader = this.loadingCtrl.create();

  Observable.fromPromise(loader.present()).switchMap(() => { //1
    return this.database.list('/notes').valueChanges(); //2
  }).subscribe((list) => { //3
    this.notesList = list; //4
    loader.dismiss();
  });
}

reorderItem( indexes ) {
  this.notesList = reorderArray(this.notesList, indexes);
}
  1. execute promise loader.present "the rxjs way"
  2. switch to the second Observable. .valueChanges() returns an Observable.
  3. subscribe to second Observable to get the streamd value
  4. write the value to this.notesList to trigger UI-Bindings

Edit

<span>{{ (notesList | async)?.length }}</span>
should now be
<span>{{ notesList?.length }}</span>
since notesList is no longer asynchronous.

There are multiple ways to display values streamed through observable pipes. One method involves using the async pipe in the template, while another approach is as explained above. The async pipe automatically subscribes to the observable and retrieves the value, but it may not allow for easy reordering of items like the manual method demonstrated here.

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