【Flutter入門講座 第5回】APIからデータを取得し、端末に保存する。httpパッケージとshared_preferences

flutter pub add http shared_preferences

dependencies:
  flutter:
    sdk: flutter
  http: ^1.6.0
  shared_preferences: ^2.5.6

// 保存・API 用: Map（JSON）との変換
factory Memo.fromJson(Map<String, dynamic> json) => Memo(
  id: json['id'] as int,
  text: json['text'] as String,
  done: json['done'] as bool? ?? false,
);

Map<String, dynamic> toJson() => {'id': id, 'text': text, 'done': done};

import 'dart:convert';

import 'package:http/http.dart' as http;

/// 練習用の公開 API（JSONPlaceholder）から、メモの候補を 1 件取ってくる
class SuggestionApi {
  SuggestionApi({http.Client? client}) : _client = client ?? http.Client();

  final http.Client _client;

  Future<String> fetchSuggestion(int id) async {
    final uri = Uri.https('jsonplaceholder.typicode.com', '/todos/$id');
    final response = await _client.get(uri);
    if (response.statusCode != 200) {
      throw Exception('取得に失敗しました（${response.statusCode}）');
    }
    // 日本語が文字化けしないよう、バイト列を UTF-8 として読む
    final json =
        jsonDecode(utf8.decode(response.bodyBytes)) as Map<String, dynamic>;
    return json['title'] as String;
  }
}

Future<void> _addSuggestion(BuildContext context) async {
  final messenger = ScaffoldMessenger.of(context);
  try {
    final text = await api.fetchSuggestion(store.memos.length + 1);
    store.add(text);
  } catch (e) {
    messenger.showSnackBar(SnackBar(content: Text('$e')));
  }
}

import 'dart:convert';

import 'package:shared_preferences/shared_preferences.dart';

import 'memo.dart';

/// メモの保存先。テストでは InMemoryMemoRepository に差し替える
abstract interface class MemoRepository {
  Future<List<Memo>> load();
  Future<void> save(List<Memo> memos);
}

/// 端末に保存する（shared_preferences の新しい API: SharedPreferencesAsync）
class LocalMemoRepository implements MemoRepository {
  static const _key = 'memos';
  final _prefs = SharedPreferencesAsync();

  @override
  Future<List<Memo>> load() async {
    final json = await _prefs.getString(_key);
    if (json == null) return [];
    final list = jsonDecode(json) as List<dynamic>;
    return [
      for (final item in list) Memo.fromJson(item as Map<String, dynamic>),
    ];
  }

  @override
  Future<void> save(List<Memo> memos) =>
      _prefs.setString(_key, jsonEncode([for (final m in memos) m.toJson()]));
}

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final store = MemoStore(LocalMemoRepository());
  await store.load();
  runApp(MemoApp(store: store, api: SuggestionApi()));
}

<manifest xmlns:android="http://schemas.android.com/apk/res/android">
    <uses-permission android:name="android.permission.INTERNET"/>
    <application ...>