loadingController.ts

constructor(
    public navCtrl: NavController,
    public navParams: NavParams, 
    public comerciosProvider : ComerciosProvider, 
    public loadingCtrl: LoadingController,
    public toastCtrl: ToastController) {     }

   ionViewDidLoad() {
    this.presentLoading();
  }
  presentLoading() {
    let loader = this.loadingCtrl.create({
      content: "Cargando...",
    });
    loader.present();
    

    setTimeout(() => {
      this.getCategorias();
      this.getOfertas();
      this.getNoticias();
      loader.dismiss();
    }, 3000);
  }