import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  //Flutter2.2.0 之后需要注意把 Key 改为可空类型 {Key? key} 表示 key 为可空类型

  const MyApp({Key? key}) : super(key: key);

  @override

  Widget build(BuildContext context) {

    return MaterialApp(

        home: Scaffold(

      appBar: AppBar(title: Text('有状态的组件')),

      body: HomePage(),

    ));

  }

}

class HomePage extends StatefulWidget {

  //Flutter2.2.0 之后需要注意把 Key 改为可空类型 {Key? key} 表示 key 为可空类型

  HomePage({Key? key}) : super(key: key);

  _HomePageState createState() => _HomePageState();

}

class _HomePageState extends State<HomePage> {

  int count = 0;

  @override

  Widget build(BuildContext context) {

    return Container(

        child: Column(

      children: <Widget>[

        Chip(label: Text("${this.count}")),

        RaisedButton(

          child: Text('增加'),

          onPressed: () {

            // print(this.count);

            setState(() {

              this.count++;

            });

          },

        )

      ],

    ));

  }

}