【Flutter】StatefulWidgetについて

class ${widgetClass} extends StatefulWidget {
	
	@override
	ステートクラス createState() => ステートクラス();
}

stateクラスの場合は、Widget build(BuildContent context) だった

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  final title = 'Flutterサンプル';
  final message = 'サンプルメッセージ';

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(
        title: this.title,
        message: this.message
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;
  final String message;
  const MyHomePage({
    Key? key,
    required this.title,
    required this.message
}): super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold (
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Text(
        widget.message,
        style: TextStyle(fontSize:32.0),
      )
    );
  }
}

_MyHomePageState createState() => _MyHomePageState(); のところをステートの処理に従って変化するよに処理を作成すれば良い

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  final title = 'Flutterサンプル';

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(
        title: this.title,
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({
    required this.title,
}): super();
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _message = 'Hello!';

  void _setMessage(){
    setState((){
      _message = 'タップしました！';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold (
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Text(
        _message,
        style: TextStyle(fontSize:32.0),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _setMessage,
        tooltip: 'set message',
        child: Icon(Icons.star),
      ),
    );
  }
}