flutter的widget之有状态statefulwidget和无状态statelesswidget

import 'package:flutter/widgets.dart';

void main() => runApp(const MyApp)

//无状态组件开始
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // 根Widget
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: '第一个StatefulWidget',
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: const MyHomePage(title: 'StatefulWidget'),
    );
  }
}
//无状态组件结束

//有状态组件开始
class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}
//有状态组件结束