Loading asyn data with ion-refresher

I am using ion-refresher to refresh my code but the code does no displays the list of datasets on refresh or on without refresh.Here is my code below:


<ion-content padding>
    <ion-refresher (ionRefresh)="doRefresh($event)">
      <ion-refresher-content refreshingText="Refreshing...">
      <ion-item *ngFor="let data of datas | async" class="pqr">
        <ion-thumbnail item-left>
          <img src="assets/image/{{data.imageName}}">
        {{data.Comp}}<br> {{data.Demand}}
        <p> {{data.Desig}}<br></p>
        {{data.Place}}<br> {{data.when}}


export class HomePage implements OnInit {
  datas: FirebaseListObservable<any[]>;
  // datas: FirebaseListObservable<Item[]>;

  constructor(public navCtrl: NavController, public authData: AuthData, public af: AngularFire) {
  ngOnInit() {
    this.datas = this.af.database.list('/datas');
doRefresh(refresher) {
   console.log('Begin async operation', refresher);

  setTimeout(() => {
  console.log('Async operation has ended');
    }, 2000);