Combining Providers Riverpod - flutter

Question

i'm trying to learn Riverpod and i use this example below to combine two providers, but the value of the dropDownButton never change and stay as the first value of the first dropDownItem , i changed the ConsumerWidget to ConsumerStatefulWidget also and nothing change, if there any help please.
final cityProvider = StateProvider<String>((ref) => 'Country one');
final weatherProvider = StateProvider((ref) {
final city = ref.watch(cityProvider);
return city == 'Country one'
? '25'
: city == 'Country two'
? '30'
: '50';
});
class ExampleSeven extends StatelessWidget {
const ExampleSeven({super.key});
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Combining Providers with Firebase'),
),
body: Center(
child: ElevatedButton(
onPressed: () {
Navigator.of(context).push(MaterialPageRoute(
builder: (context) => const SecondScreen(),
));
},
child: const Text('Go to next Page')),
),
);
}
}
class SecondScreen extends ConsumerWidget {
const SecondScreen({super.key});
#override
Widget build(BuildContext context, ref) {
String? city = ref.watch(cityProvider);
final weather = ref.watch(weatherProvider);
return Scaffold(
appBar: AppBar(
title: const Text('Combining Providers Second Screen'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
DropdownButton(
value: city,
items: const [
DropdownMenuItem(
value: 'Country one',
child: Text('Country one'),
),
DropdownMenuItem(
value: 'Country two',
child: Text('Country two'),
),
DropdownMenuItem(
value: 'Country three',
child: Text('Country three'),
),
],
onChanged: (value) {
city = value;
},
),
Text(
weather,
style: const TextStyle(fontSize: 40),
),
],
),
));
}
}
may i need to change the first Class or need to use listen instead of read ?

Answer 1

You're not updating the value of the provider correctly. Change you onChanged method to
onChanged: (value) {
ref.read(cityProvider.notifier).state = value!;
},