Flutter 官方状态管理 Provider基本使用

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
 
void main() {
  runApp(MyApp());
}
 
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}
 
class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
 
  final String title;
 
  @override
  _MyHomePageState createState() => _MyHomePageState();
}
 
class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Consumer<Counter>(
              builder: (context, counter, _) => Text(
                '${counter.count}',
                style: Theme.of(context).textTheme.headline4,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => Provider.of<Counter>(context, listen: false).increment(),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}
 
class Counter with ChangeNotifier {
  int _count = 0;
  int get count => _count;
  void increment() {
    _count++;
    notifyListeners();
  }
}

这段代码使用了Provider包来创建一个简单的状态管理模式。它定义了一个Counter类，使用ChangeNotifier来通知监听它的widgets状态发生了变化。在MyHomePage中，我们使用Consumer来重建widget树，以便当Counter的状态改变时，UI能够更新。这个例子展示了如何在Flutter应用中实现状态管理，并且是学习和使用Provider的一个很好的起点。