【Flutter/Dart】シンプルなカウンターアプリを作る

import 'package:flutter/material.dart';

void main() {
  runApp(CounterApp());
}

class CounterApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CounterScreen(),
    );
  }
}

class CounterScreen extends StatefulWidget {
  @override
  _CounterScreenState createState() => _CounterScreenState();
}

class _CounterScreenState extends State<CounterScreen> {
  int _counter = 0;

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

  void _decrementCounter() {
    setState(() {
      _counter--;
    });
  }

  void _resetCounter() {
    setState(() {
      _counter = 0;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Counter App'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              '$_counter',
              style: TextStyle(fontSize: 48),
            ),
            SizedBox(height: 16),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                ElevatedButton(
                  onPressed: _decrementCounter,
                  child: Text('-'),
                ),
                SizedBox(width: 16),
                ElevatedButton(
                  onPressed: _resetCounter,
                  child: Text('Reset'),
                ),
                SizedBox(width: 16),
                ElevatedButton(
                  onPressed: _incrementCounter,
                  child: Text('+'),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}