Flutter Provider value is null - flutter

Question

I'm trying to pass an index from a widget to another through a provider but the value returns by the provider context seems empty.
#override
Widget build(BuildContext context) {
return ChangeNotifierProvider(
create:(ctx)=> ProvideIDX(),
child: Scaffold(
body: Container(
child: Stack(
children: <Widget>[
Maposm(lieu), //, idcarousel), // Pass index to this class
Align(
alignment: Alignment.bottomCenter,
child: CarouselSlider.builder(
itemCount: lieu.length,
itemBuilder: (BuildContext ctx, index) {
return Container(
color: Colors.yellow, child:Text(lieu[index].name));
},
options: CarouselOptions(
enableInfiniteScroll: true,
scrollDirection: Axis.horizontal,
onPageChanged: (index, reason) {
setState(() {
Index(id: index);
print(index);
});
},
)),
),
],
),
)));
}
}
class Places {
String name;
LatLng coordxy;
Places({this.name, this.coordxy});
}
class Index {
int id;
Index({this.id});
}
class ProvideIDX with ChangeNotifier{
Index _selectedID;
set selectedID(id){
this._selectedID = id;
notifyListeners();
}
get selectedID=>this._selectedID;
}
And the provider is called inside Maposm class like this :
#override
Widget build(BuildContext context) {
final _passIDX= Provider.of<ProvideIDX>(context);
final id = _passIDX.selectedID;
print(id); // show null
and the result I got is "null", which of course is not the value I'd like to use ^^
edit: Even if the code is reduced it appears to be too long for the post. I uploaded the two classes and the yaml on Gdrive

Answer 1

Instead of:
final _passIDX= Provider.of<ProvideIDX>(context);
you should watch your provider:
final _passIDX = context.watch<ProvideIDX>();
Here is a Minimal Working Example:
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
void main() {
runApp(
ChangeNotifierProvider(
create: (ctx) => ProvideIDX(),
child: MaterialApp(
debugShowCheckedModeBanner: false,
title: 'Flutter Demo',
home: HomePage(),
),
),
);
}
class HomePage extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: _Child(),
),
floatingActionButton: FloatingActionButton(
onPressed: () =>
Provider.of<ProvideIDX>(context, listen: false).increment(),
child: Icon(Icons.add),
),
);
}
}
class _Child extends StatelessWidget {
#override
Widget build(BuildContext context) {
final _passIDX = context.watch<ProvideIDX>();
return Text(
_passIDX.selectedID.toString(),
style: TextStyle(fontSize: 96.0),
);
}
}
class Places {
String name;
Offset coordxy;
Places({this.name, this.coordxy});
}
class Index {
int id;
Index({this.id});
increment() => id++;
toString() => id.toString();
}
class ProvideIDX with ChangeNotifier {
Index _selectedID = Index(id: 0);
get selectedID => _selectedID;
set selectedID(id) {
_selectedID = id;
notifyListeners();
}
void increment() {
_selectedID.increment();
notifyListeners();
}
}