Flutter: How To Change/Refresh State From Another Widget - flutter

Question

I am trying to have a global integer that is displayed in a widget and then is updated by something (a button click or something) from another widget. All of the other ways i have tried don't work. What is the best way to do this?
Stack overflow says i have too much code so more text more text more text
import 'package:flutter/material.dart';
void main() {
runApp(
MaterialApp(
home: Scaffold(
body: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
ScoreDisplay(),
PointButton(),
],
),
),
),
),
);
}
int score = 0;
class ScoreDisplay extends StatefulWidget {
#override
_ScoreDisplayState createState() => _ScoreDisplayState();
}
class _ScoreDisplayState extends State<ScoreDisplay> {
#override
Widget build(BuildContext context) {
return Center(
child: Container(
child: Text(
'Score: $score',
),
),
);
}
}
class PointButton extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Center(
child: Container(
child: RaisedButton(
//onPressed: //increment score,
),
),
);
}
}

Answer 1

You need to implement some kind of State Management for that.
Here are two basic ways to implement such a feature: with a StatefulWidget and with Riverpod.
1. With a StatefulWidget
I extracted your Scaffold as a StatefulWidget maintaining the score of your application.
I then use ScoreDisplay as a pure StatelessWidget receiving the score as a parameter. And your PointButton is also Stateless and call the ScorePage thanks to a simple VoidCallback function.
Full source code:
import 'package:flutter/material.dart';
void main() {
runApp(
MaterialApp(
home: ScorePage(),
),
);
}
class ScorePage extends StatefulWidget {
const ScorePage({
Key key,
}) : super(key: key);
#override
_ScorePageState createState() => _ScorePageState();
}
class _ScorePageState extends State<ScorePage> {
int score = 0;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
ScoreDisplay(score: score),
PointButton(onIncrement: () => setState(() => score++)),
],
),
),
);
}
}
class ScoreDisplay extends StatelessWidget {
final int score;
const ScoreDisplay({Key key, this.score}) : super(key: key);
#override
Widget build(BuildContext context) {
return Center(
child: Container(
child: Text(
'Score: $score',
),
),
);
}
}
class PointButton extends StatelessWidget {
final VoidCallback onIncrement;
const PointButton({Key key, this.onIncrement}) : super(key: key);
#override
Widget build(BuildContext context) {
return Center(
child: Container(
child: ElevatedButton(
onPressed: () => onIncrement?.call(),
child: Text('CLICK ME'),
),
),
);
}
}
2. With Riverpod
Create a StateProvider:
final scoreProvider = StateProvider<int>((ref) => 0);
Watch the StateProvider:
final score = useProvider(scoreProvider).state;
Update the StateProvider
context.read(scoreProvider).state++
Full Source Code
import 'package:flutter/material.dart';
import 'package:flutter_hooks/flutter_hooks.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';
void main() {
runApp(
ProviderScope(
child: MaterialApp(
home: Scaffold(
body: Container(
child: Column(
mainAxisAlignment: MainAxisAlignment.spaceEvenly,
children: [
ScoreDisplay(),
PointButton(),
],
),
),
),
),
),
);
}
int score = 0;
class ScoreDisplay extends HookWidget {
#override
Widget build(BuildContext context) {
final score = useProvider(scoreProvider).state;
return Center(
child: Container(
child: Text(
'Score: $score',
),
),
);
}
}
class PointButton extends StatelessWidget {
#override
Widget build(BuildContext context) {
return Center(
child: Container(
child: ElevatedButton(
onPressed: () => context.read(scoreProvider).state++,
child: Text('CLICK ME'),
),
),
);
}
}
final scoreProvider = StateProvider<int>((ref) => 0);
Check Riverpod Website for more info and more advanced use cases.
But you have many more flavors of State Management available.

Answer 2

The best example is to use "provider" package which can be found on www.pub.dev
It is very easy state management package that can help You solve this problem. Keep in my that provider instead of setState() uses notifyListener()