【Flutter】Stateless Widget・Stateful Widget違いを3分で解説!（サンプルコードあり）

import 'package:flutter/material.dart';
import 'dart:math';

void main() => runApp(StatelessDemo());

class StatelessDemo extends StatelessWidget {
  int chkNumber = 0;
  Random rdmNumber = new Random();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('数字は　' + (chkNumber == 1 ? '1' : '0')),
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.numbers_rounded),
          onPressed: () {
            chkNumber = rdmNumber.nextInt(2);
            print(chkNumber);
          },
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';
import 'dart:math';

void main() => runApp(MyHomePage());

class MyHomePage extends StatefulWidget {
  @override
  State<MyHomePage> createState() => _StatefulDemo();
}

class _StatefulDemo extends State<MyHomePage> {
  int chkNumber = 0;
  Random rdmNumber = new Random();

  @override
  void initState() {
    print("初期処理");
     super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('数字は　' + (chkNumber == 1 ? '1' : '0')),
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.attach_money),
          onPressed: () {
            setState(() {
              chkNumber = rdmNumber.nextInt(2);
            });
            print(chkNumber);
          },
        ),
      ),
    );
  }
}