Where to pass the navCtrl to child page?

Ionic Framework ionic-v3
1

I was seeing the tutorial of ionic 2 and read the class of ItemDetailsPage which is a child page in a ListPage:

@Component({
  templateUrl: 'item-details.html'
})
export class ItemDetailsPage {
  selectedItem: any;

  constructor(public navCtrl: NavController, public navParams: NavParams) {
    // If we navigated to this page, we will have an item available as a nav param
    this.selectedItem = navParams.get('item');
  }
}

but I don’t see any codes to pass the navCtrl to ItemDetailsPage,instead I only see

itemTapped(event, item) {
    this.navCtrl.push(ItemDetailsPage, {
      item: item
    });
  }

, where is the place to pass the current navigation controller to the child page?