【 Flutter 】Flutter を 基礎 から 学習 ( Material ComponentsとiOS-Style ) part123 Material Components

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(home: new MyHomePage()));
}

class MyHomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _MyHomePageState();
  }
}

class _MyHomePageState extends State<MyHomePage> {
  bool dark = false;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: dark ? ThemeData.dark() : ThemeData.light(),
      home: Scaffold(
        appBar: AppBar(title: Text('Toggle theme sample')),
        body: Center(
          child: ElevatedButton(
            onPressed: () {
              setState(() => dark = !dark);
            },
            child: Text('Toggle theme'),
          ),
        ),
      ),
    );
  }
}