Slider not updating itself - flutter

Question

I saw another StackOverflow post, none of that worked for me.
I am a flutter newbie.
I am showing modal bottom sheet from a stateful widget called 'Home'
showMaterialModalBottomSheet(
context: context,
bounce: true,
duration: const Duration(milliseconds: 600),
builder: (context) => SingleChildScrollView(
controller: ModalScrollController.of(context),
child: bookmark(id: books[index]['_id'], totalPages: int.parse(books[index]['total']), completedPages: int.parse(books[index]['done']),);
//another 'Stateful widget'
),
);
Another stateful widget name 'bookmark' looks like this
int toggleIndex = 0;
double dragPercentage = 0;
double dragUpdate = 0;
//variables common to both main widget and this widget
class bookmark extends StatefulWidget {
final int totalPages;
final int completedPages;
final int id;
bookmark({#required this.completedPages, #required this.totalPages, #required this.id});
#override
State<bookmark> createState() => _bookmarkState();
}
class _bookmarkState extends State<bookmark> {
#override
Widget build(BuildContext context) {
return
Container(
child: Column(
children: [
Padding(
padding: const EdgeInsets.symmetric(horizontal: 10),
child: SizedBox(
width: double.maxFinite,
child: CupertinoSlider(
value: dragUpdate,
max: 100,
min: 0,
onChanged: (double dragUpdate) {
setState(() {
dragUpdate = dragUpdate;
dragPercentage = dragUpdate * widget.totalPages;
pages.text = (dragPercentage / 100.0).toStringAsFixed(0);
});
},
),
),
),
],
)
);
}
}
The slider is updating the value but is not updating itself.
to be clear, there are 2 stateful widgets named home and bookmark. I am calling showMaterialModalBottomSheet from home and building a bookmark.
what I tried?
I already tried to wrap my slider with a statefulbuilder and used its state to update the values.