每次调用 BlocProvider 时,都会创建 bloc 类的新实例。
要使用相同的块实例,您需要创建它一次,并将其放在路由之前,之后您将可以通过上下文访问它。
import 'package:bloc/bloc.dart';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MultiBlocProvider(
providers: [
BlocProvider<BlocSample>(
create: (BuildContext context) => BlocSample(),
),
],
child: MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: FirstScreen(),
),
);
}
}
class BlocSample extends Bloc<EventSample, String> {
@override
String get initialState => 'initial state';
@override
Stream<String> mapEventToState(
EventSample event,
) async* {
yield 'changed state';
}
}
class EventSample {}
class FirstScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return BlocBuilder<BlocSample, String>(
builder: (context, state) {
return Scaffold(
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(state),
RaisedButton(
child: Text('change status'),
onPressed: () => BlocProvider.of<BlocSample>(context).add(
EventSample(),
),
),
RaisedButton(
child: Text('change route'),
onPressed: () => Navigator.of(context).push(
MaterialPageRoute(
builder: (_) => SecondScreen(),
),
),
)
],
),
),
);
},
);
}
}
class SecondScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return BlocBuilder<BlocSample, String>(
builder: (context, state) {
return Scaffold(
body: Center(child: Text(state)),
);
},
);
}
}