How to use the onsenui.openActionSheet function in onsenui

openActionSheet(todo: Todo) {
    ons.openActionSheet({
      cancelable: true,
      title: 'Do you want to delete this item ?',
      buttons: [
        { label: 'Delete', icon: 'md-delete', modifier: 'destructive' },
        { label: 'Cancel', icon: 'md-close' }
      ],
    }).then((i: number) => {
      switch (i) {
        case 0:
          this.delete(todo);
          break;
        default:
          break;
      }
    });
  }