The following is a example code from :
https://bloclibrary.dev/#/flutterbloccoreconcepts
I am getting the following exception,
How can I fix the following Exception and why is this happening:
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building CounterPage(dirty):
BlocProvider.of() called with a context that does not contain a Cubit of type CounterBloc.
No ancestor could be found starting from the context that was passed to BlocProvider.of().
This can happen if the context you used comes from a widget above the BlocProvider.
The context used was: CounterPage(dirty)
main.dart
import 'package:flutter/material.dart';
import 'counter_page.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Bloc Counter Example',
home: CounterPage(),
);
}
}
counter_page.dart
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import'package:flutterbloc_counter_app/counter_bloc.dart';
class CounterPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
final CounterBloc counterBloc = BlocProvider.of<CounterBloc>(context);
return Scaffold(
appBar: AppBar(title: Text('Counter')),
body: BlocBuilder<CounterBloc, int>(
builder: (context, count) {
return Center(
child: Text(
'$count',
style: TextStyle(fontSize: 24.0),
),
);
},
),
floatingActionButton: Column(
crossAxisAlignment: CrossAxisAlignment.end,
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Padding(
padding: EdgeInsets.symmetric(vertical: 5.0),
child: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () {
counterBloc.add(CounterEvent.increment);
},
),
),
Padding(
padding: EdgeInsets.symmetric(vertical: 5.0),
child: FloatingActionButton(
child: Icon(Icons.remove),
onPressed: () {
counterBloc.add(CounterEvent.decrement);
},
),
),
],
),
);
}
}
counter_bloc.dart
import 'package:flutter_bloc/flutter_bloc.dart';
enum CounterEvent { increment, decrement }
class CounterBloc extends Bloc<CounterEvent, int> {
CounterBloc() : super(0);
@override
Stream<int> mapEventToState(CounterEvent event) async* {
switch (event) {
case CounterEvent.decrement:
yield state - 1;
break;
case CounterEvent.increment:
yield state + 1;
break;
}
}
}
You can not use 'BlocProvider.of' without BlocProvider at the parent.
You just create a 'CounterBloc' and pass the bloc to BlocBuilder.
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import'package:flutterbloc_counter_app/counter_bloc.dart';
class CounterPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
final CounterBloc counterBloc = CounterBloc();
return Scaffold(
appBar: AppBar(title: Text('Counter')),
body: BlocBuilder<CounterBloc, int>(
bloc: counterBloc,
builder: (context, count) {
return Center(
child: Text(
'$count',
style: TextStyle(fontSize: 24.0),
),
);
},
),
floatingActionButton: Column(
crossAxisAlignment: CrossAxisAlignment.end,
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
Padding(
padding: EdgeInsets.symmetric(vertical: 5.0),
child: FloatingActionButton(
child: Icon(Icons.add),
onPressed: () {
counterBloc.add(CounterEvent.increment);
},
),
),
Padding(
padding: EdgeInsets.symmetric(vertical: 5.0),
child: FloatingActionButton(
child: Icon(Icons.remove),
onPressed: () {
counterBloc.add(CounterEvent.decrement);
},
),
),
],
),
);
}
}
It looks like I forgot to provide an instance of the bloc to the CounterPage. Wrapping the CounterPage widget in a BlocProvider and create the instance of the bloc like this will do the trick:
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Bloc Counter Example',
home: BlocProvider(
create: (context) => CounterBloc(),
child: CounterPage(),
),
);
}
}
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