计数器

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

main() {
  runApp(DBJApp());
}

class DBJApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(primaryColor: Colors.green),
      home: Scaffold(
        appBar: AppBar(
          title: Text('计数器'),
        ),
        body: DBJHomeBody('传递一个message'),
      ),
    );
  }
}

class DBJHomeBody extends StatefulWidget {
  final String message;
  DBJHomeBody(this.message);

  @override
  _DBJHomeBodyState createState() {
    return _DBJHomeBodyState();
  }
}

class _DBJHomeBodyState extends State<DBJHomeBody> {
  int _counter = 0;

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      // crossAxisAlignment: CrossAxisAlignment.end,
      children: <Widget>[
        _getRaiseButton(),
        SizedBox(
          height: 10,
        ),
        Text(
          '开始计数: $_counter，${this.widget.message}',
          style: TextStyle(fontSize: 15, color: Colors.green),
        ),
      ],
    );
  }

  Widget _getRaiseButton() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        TextButton(
          onPressed: () {
            print('点击加号');
            setState(() {
              _counter++;
            });
          },
          child: Text(
            '点击+',
            style: TextStyle(color: Colors.white),
          ),
          style: ButtonStyle(backgroundColor: MaterialStateProperty.all(Colors.red)),
        ),
        TextButton(
          onPressed: () {
            print('点击减号');
            setState(() {
              _counter--;
            });
          },
          child: Text(
            '点击-',
            style: TextStyle(color: Colors.white),
          ),
          style: ButtonStyle(backgroundColor: MaterialStateProperty.all(Colors.green)),
        ),
      ],
    );
  }
}

Simulator Screen Shot - iPhone 12 - 2021-09-02 at 17.13.33.png