lib/main.dart

import 'package:flutter/material.dart';

// リスト 7.6
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: CountPage());
  }
}

class CountPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _CountPageState();
}

class _CountPageState extends State<CountPage> {
  int count = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text('カウント'),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                IconButton(
                  icon: Icon(Icons.remove),
                  onPressed: () => setState(() {
                    count--;
                  }),
                ),
                Text(count.toString()),
                IconButton(
                  icon: Icon(Icons.add),
                  onPressed: () => setState(() {
                    count++;
                  }),
                )
              ],
            )
          ],
        )
      ),
    );
  }
}