BlocProvider的使用和BLoC的实例化

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

// 自定义BLoC类
class CounterBloc {
  int _counter = 0;

  // 获取当前计数
  int get counter => _counter;

  // 增加计数
  void increment() {
    _counter++;
  }
}

// 自定义BlocProvider类
class CounterBlocProvider extends BlocProvider<CounterBloc> {
  CounterBlocProvider({
    Key key,
    CounterBloc value,
    Widget child,
  }) : super(key: key, value: value, child: child);

  @override
  bool updateShouldNotify(InheritedWidget oldWidget) => true;

  // 创建CounterBloc实例
  static CounterBloc of(BuildContext context) =>
      context.dependOnInheritedWidgetOfExactType<CounterBlocProvider>().value;
}

// 使用BLoC的组件
class CounterWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // 获取CounterBloc实例
    final CounterBloc counterBloc = CounterBlocProvider.of(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('Counter App'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Counter: ${counterBloc.counter}',
              style: TextStyle(fontSize: 24),
            ),
            RaisedButton(
              child: Text('Increment'),
              onPressed: () {
                // 调用BLoC的方法增加计数
                counterBloc.increment();
              },
            ),
          ],
        ),
      ),
    );
  }
}

// 应用程序入口
void main() {
  runApp(
    // 使用BlocProvider包裹CounterWidget
    CounterBlocProvider(
      value: CounterBloc(),
      child: MaterialApp(
        home: CounterWidget(),
      ),
    ),
  );
}