最終更新:2025-01-16 (木) 04:42:13 (23d)
Flutter/プロジェクト/lib/main.dart
flutter create
クラス
クラス名 親クラス 更に親 MyApp? Flutter/StatelessWidget Flutter/Widget MyHomePage? Flutter/StatefulWidget Flutter/Widget _MyHomePage? Flutter/State<MyHomePage?> Flutter/Diagnosticable?
MyApp?
- コンストラクタ
- build
MyHomePage?
- コンストラクタ
- createState
_MyHomePage?
- build
- Flutter/Scaffold
- appBar: Flutter/AppBar
- body: Flutter/Center
- Flutter/Scaffold
コード
import 'package:flutter/material.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); // This widget is the root of your application. @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter Demo', theme: ThemeData( // This is the theme of your application. // // TRY THIS: Try running your application with "flutter run". You'll see // the application has a purple toolbar. Then, without quitting the app, // try changing the seedColor in the colorScheme below to Colors.green // and then invoke "hot reload" (save your changes or press the "hot // reload" button in a Flutter-supported IDE, or press "r" if you used // the command line to start the app). // // Notice that the counter didn't reset back to zero; the application // state is not lost during the reload. To reset the state, use hot // restart instead. // // This works for code too, not just values: Most code changes can be // tested with just a hot reload. colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple), useMaterial3: true, ), home: const MyHomePage(title: 'Flutter Demo Home Page'), ); } } class MyHomePage extends StatefulWidget { const MyHomePage({super.key, required this.title}); // This widget is the home page of your application. It is stateful, meaning // that it has a State object (defined below) that contains fields that affect // how it looks. // This class is the configuration for the state. It holds the values (in this // case the title) provided by the parent (in this case the App widget) and // used by the build method of the State. Fields in a Widget subclass are // always marked "final". final String title; @override State<MyHomePage> createState() => _MyHomePageState(); } class _MyHomePageState extends State<MyHomePage> { int _counter = 0; void _incrementCounter() { setState(() { // This call to setState tells the Flutter framework that something has // changed in this State, which causes it to rerun the build method below // so that the display can reflect the updated values. If we changed // _counter without calling setState(), then the build method would not be // called again, and so nothing would appear to happen. _counter++; }); } @override Widget build(BuildContext context) { // This method is rerun every time setState is called, for instance as done // by the _incrementCounter method above. // // The Flutter framework has been optimized to make rerunning build methods // fast, so that you can just rebuild anything that needs updating rather // than having to individually change instances of widgets. return Scaffold( appBar: AppBar( // TRY THIS: Try changing the color here to a specific color (to // Colors.amber, perhaps?) and trigger a hot reload to see the AppBar // change color while the other colors stay the same. backgroundColor: Theme.of(context).colorScheme.inversePrimary, // Here we take the value from the MyHomePage object that was created by // the App.build method, and use it to set our appbar title. title: Text(widget.title), ), body: Center( // Center is a layout widget. It takes a single child and positions it // in the middle of the parent. child: Column( // Column is also a layout widget. It takes a list of children and // arranges them vertically. By default, it sizes itself to fit its // children horizontally, and tries to be as tall as its parent. // // Column has various properties to control how it sizes itself and // how it positions its children. Here we use mainAxisAlignment to // center the children vertically; the main axis here is the vertical // axis because Columns are vertical (the cross axis would be // horizontal). // // TRY THIS: Invoke "debug painting" (choose the "Toggle Debug Paint" // action in the IDE, or press "p" in the console), to see the // wireframe for each widget. mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ const Text( 'You have pushed the button this many times:', ), Text( '$_counter', style: Theme.of(context).textTheme.headlineMedium, ), ], ), ), floatingActionButton: FloatingActionButton( onPressed: _incrementCounter, tooltip: 'Increment', child: const Icon(Icons.add), ), // This trailing comma makes auto-formatting nicer for build methods. ); } }
解説
import 'package:flutter/material.dart'; void main() { runApp(const MyApp()); } class MyApp extends StatelessWidget { const MyApp({super.key}); // アプリケーションのルートウィジェット @override Widget build(BuildContext context) { return MaterialApp( title: 'Flutter デモ', // アプリケーションのタイトル theme: ThemeData( // アプリケーションのテーマを定義 // 実験: "flutter run" でアプリを起動後、seedColor を Colors.green に変更し、ホットリロードを試してください colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple), useMaterial3: true, // Material3 のデザインを適用 ), home: const MyHomePage(title: 'Flutter デモ ホームページ'), // ホーム画面を設定 ); } } class MyHomePage extends StatefulWidget { const MyHomePage({super.key, required this.title}); // コンストラクタ: 必須の title パラメータを受け取る // このクラスはホームページの設定を保持 // 今回の例では title を保持しています final String title; // ホームページのタイトル @override State<MyHomePage> createState() => _MyHomePageState(); } class _MyHomePageState extends State<MyHomePage> { int _counter = 0; // ボタンが押された回数を保持するカウンター // カウンターを増加させるメソッド void _incrementCounter() { setState(() { // setState を呼び出すことで、状態が変更されたことをフレームワークに通知 _counter++; }); } @override Widget build(BuildContext context) { // setState が呼び出されるたびに再実行されます return Scaffold( appBar: AppBar( // アプリの上部バー backgroundColor: Theme.of(context).colorScheme.inversePrimary, // 色をテーマから取得 title: Text(widget.title), // タイトルを表示 ), body: Center( // 画面中央にウィジェットを配置 child: Column( mainAxisAlignment: MainAxisAlignment.center, // 子ウィジェットを縦方向に中央揃え children: <Widget>[ const Text( 'ボタンを押した回数:', // 説明文 ), Text( '$_counter', // カウンターの値を表示 style: Theme.of(context).textTheme.headlineMedium, // テーマのスタイルを適用 ), ], ), ), floatingActionButton: FloatingActionButton( onPressed: _incrementCounter, // ボタンが押されたときにカウンターを増加 tooltip: 'インクリメント', // ツールチップ(長押し時に表示されるテキスト) child: const Icon(Icons.add), // プラスアイコン ), // trailing comma はコードフォーマットを見やすくします ); } }
関連
- Flutter/ThemeData?
- Flutter/ColorScheme?
- Flutter/Colors