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[英]How to provide context to BlocProvider.of without using BlocBuilder in flutter bloc
[英]When to provide a bloc in a BlocBuilder()?
我正在尝试将 cubit 用于 flutter 计数器应用程序。 我想知道何时为 BlocBuilder() 中的 bloc 参数提供 Bloc/Cubit。 我尝试为以下代码提供一个,但它不起作用并出现错误:
Error: Could not find the correct Provider<CounterCubit> above this CounterPage Widget
.
class CounterPage extends StatelessWidget {
const CounterPage({Key? key, required this.title}) : super(key: key);
final String title;
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(title),
centerTitle: true,
),
body: BlocBuilder<CounterCubit, int>(
bloc: CounterCubit(),
builder: (_, count) => Center(
child: Text('$count'),
)),
floatingActionButton: Row(
mainAxisAlignment: MainAxisAlignment.end,
children: [
Padding(
padding: const EdgeInsets.all(8.0),
child: FloatingActionButton(
onPressed: () => context.read<CounterCubit>().increment(),
tooltip: 'Increment',
child: Icon(Icons.add),
),
),
Padding(
padding: const EdgeInsets.all(8.0),
child: FloatingActionButton(
onPressed: () => context.read<CounterCubit>().decrement(),
tooltip: 'Decrement',
child: Icon(Icons.remove),
),
),
],
),
);
}
}
这是肘的代码。
import 'package:flutter_bloc/flutter_bloc.dart';
class CounterCubit extends Cubit<int> {
CounterCubit() : super(0);
void increment() => emit(state + 1);
void decrement() => emit(state - 1);
}
来自官方文档:
仅当您希望提供一个范围为单个小部件且无法通过父 BlocProvider 和当前 BuildContext 访问的 bloc 时才指定 bloc。
BlocBuilder<BlocA, BlocAState>(
bloc: blocA, // provide the local bloc instance
builder: (context, state) {
// return widget here based on BlocA's state
}
)
在您的情况下,我建议您将 BLoC 提供给CounterPage
上方的小部件树,如下所示:
BlocProvider<CounterCubit>(
create: (BuildContext context) => CounterCubit(),
child: CounterPage(),
);
然后,在BlocBuilder
中,您不需要指定bloc
属性:
...
body: BlocBuilder<CounterCubit, int>(
builder: (_, count) => Center(
child: Text('$count'),
)),
...
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