async public void OnDelete(object sender, EventArgs e)
        {
            var     menuItem = ((MenuItem)sender);
            Rubrica rubrica  = menuItem.CommandParameter as Rubrica;

            await firebase
            .Child(Utils.FireBase_Entity.RUBRICAS)
            .Child(rubrica.Uid)
            .DeleteAsync();

            await FirebaseDB.getRubricas(rubricasCollection);
        }
 protected async override void OnAppearing()
 {
     base.OnAppearing();
     await FirebaseDB.getRubricas(rubricasCollection);
 }