Flutterにおけるローカルデータの保存と読み出しについてのチュートリアル

flutter pub add shared_preferences

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Shared Preferences Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  String data = '';

  @override
  void initState() {
    super.initState();
    loadSavedData();
  }

  Future loadSavedData() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    setState(() {
      data = prefs.getString('my_data_key') ?? '';
    });
  }

  Future saveData(String value) async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.setString('my_data_key', value);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Shared Preferences Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'Saved Data: $data',
            ),
            TextField(
              onSubmitted: saveData,
            ),
          ],
        ),
      ),
    );
  }
}