Local Storage

1. Spectrum lưu trữ local

2. shared_preferences

flutter pub add shared_preferences

import 'package:shared_preferences/shared_preferences.dart';

final prefs = await SharedPreferences.getInstance();

// Write
await prefs.setString('name', 'Việt');
await prefs.setInt('age', 25);
await prefs.setBool('premium', true);
await prefs.setDouble('balance', 99.5);
await prefs.setStringList('tags', ['flutter', 'dart']);

// Read — sync (đã getInstance trước đó)
final name = prefs.getString('name');   // nullable
final age = prefs.getInt('age') ?? 0;

// Delete
await prefs.remove('name');
await prefs.clear();        // xóa tất cả

Wrapper class — typed access

class AppPrefs {
  final SharedPreferences _prefs;
  AppPrefs(this._prefs);

  static Future<AppPrefs> create() async {
    return AppPrefs(await SharedPreferences.getInstance());
  }

  ThemeMode get themeMode {
    final i = _prefs.getInt('themeMode') ?? 0;
    return ThemeMode.values[i];
  }
  Future<void> setThemeMode(ThemeMode m) => _prefs.setInt('themeMode', m.index);

  bool get hasSeenIntro => _prefs.getBool('hasSeenIntro') ?? false;
  Future<void> markIntroSeen() => _prefs.setBool('hasSeenIntro', true);
}

Type-safe + tránh string key rải khắp code.

3. flutter_secure_storage

flutter pub add flutter_secure_storage

import 'package:flutter_secure_storage/flutter_secure_storage.dart';

const storage = FlutterSecureStorage();

// Write
await storage.write(key: 'jwt', value: 'eyJhbGc...');

// Read
final token = await storage.read(key: 'jwt');

// Delete
await storage.delete(key: 'jwt');
await storage.deleteAll();

Storage layer per platform:

• iOS — Keychain (system encryption).
• Android — EncryptedSharedPreferences (Keystore-backed).
• macOS — Keychain.
• Linux — libsecret.
• Windows — Windows Credential Manager.
• Web — không support (browser không có Keychain — dùng IndexedDB encrypted).

4. File system — path_provider + dart:io

flutter pub add path_provider

import 'package:path_provider/path_provider.dart';
import 'dart:io';

// Documents directory — backup khi user backup device, persistent
final docs = await getApplicationDocumentsDirectory();

// Cache directory — OS có thể clear khi cần memory
final cache = await getTemporaryDirectory();

// Write file
final file = File('${docs.path}/data.json');
await file.writeAsString(jsonEncode({'key': 'value'}));

// Read
if (await file.exists()) {
  final content = await file.readAsString();
  print(jsonDecode(content));
}

5. sqflite — SQLite

flutter pub add sqflite path

import 'package:sqflite/sqflite.dart';
import 'package:path/path.dart';

Future<Database> openDb() async {
  final dbPath = join(await getDatabasesPath(), 'notes.db');
  return openDatabase(
    dbPath,
    version: 1,
    onCreate: (db, version) async {
      await db.execute('''
        CREATE TABLE notes (
          id INTEGER PRIMARY KEY AUTOINCREMENT,
          title TEXT NOT NULL,
          body TEXT,
          created_at INTEGER NOT NULL
        )
      ''');
    },
  );
}

CRUD

// Insert
final id = await db.insert('notes', {
  'title': 'Học Flutter',
  'body': 'IT Basic chương 11',
  'created_at': DateTime.now().millisecondsSinceEpoch,
});

// Query — all
final all = await db.query('notes');
// List<Map<String, dynamic>>

// Query — where
final rows = await db.query(
  'notes',
  where: 'id = ?',
  whereArgs: [1],
);

// Raw SQL
final r = await db.rawQuery(
  'SELECT * FROM notes WHERE created_at > ? ORDER BY id DESC LIMIT 10',
  [DateTime.now().subtract(Duration(days: 7)).millisecondsSinceEpoch],
);

// Update
await db.update('notes', {'title': 'Updated'}, where: 'id = ?', whereArgs: [1]);

// Delete
await db.delete('notes', where: 'id = ?', whereArgs: [1]);

Migration với onUpgrade

openDatabase(
  dbPath,
  version: 2,    // tăng từ 1 → 2
  onCreate: (db, v) async {
    // Schema mới nhất
  },
  onUpgrade: (db, oldV, newV) async {
    if (oldV < 2) {
      await db.execute('ALTER TABLE notes ADD COLUMN priority INTEGER DEFAULT 0');
    }
    // Future migrations: if (oldV < 3) ...
  },
)

6. drift — SQL type-safe codegen

flutter pub add drift drift_flutter
flutter pub add --dev drift_dev build_runner

import 'package:drift/drift.dart';

part 'database.g.dart';

class Notes extends Table {
  IntColumn get id => integer().autoIncrement()();
  TextColumn get title => text().withLength(min: 1, max: 100)();
  TextColumn get body => text().nullable()();
  DateTimeColumn get createdAt => dateTime()();
}

@DriftDatabase(tables: [Notes])
class AppDb extends _$AppDb {
  AppDb() : super(_openConnection());

  @override
  int get schemaVersion => 1;

  // Type-safe query
  Future<List<Note>> recentNotes() =>
      (select(notes)..orderBy([(t) => OrderingTerm.desc(t.createdAt)])).get();

  // Watch — Stream cho real-time UI
  Stream<List<Note>> watchAll() => select(notes).watch();

  Future<int> addNote(NotesCompanion n) => into(notes).insert(n);
}

// Use
final db = AppDb();

// StreamBuilder cho real-time
StreamBuilder<List<Note>>(
  stream: db.watchAll(),
  builder: (ctx, snap) => ListView(
    children: (snap.data ?? []).map((n) => ListTile(title: Text(n.title))).toList(),
  ),
)

7. hive — NoSQL object

flutter pub add hive hive_flutter
flutter pub add --dev hive_generator build_runner

import 'package:hive/hive.dart';

part 'user.g.dart';

@HiveType(typeId: 0)
class User extends HiveObject {
  @HiveField(0)
  String name;

  @HiveField(1)
  int age;

  User({required this.name, required this.age});
}

// Init
await Hive.initFlutter();
Hive.registerAdapter(UserAdapter());

// Open box
final box = await Hive.openBox<User>('users');

// Put / get
await box.put('viet', User(name: 'Việt', age: 25));
final u = box.get('viet');

// Iterate
for (final key in box.keys) {
  print('$key: ${box.get(key)?.name}');
}

// Delete
await box.delete('viet');
await box.clear();

8. isar — modern NoSQL

Cùng author Hive nhưng next-gen: full-text search, indexes, query DSL mạnh hơn.

flutter pub add isar isar_flutter_libs
flutter pub add --dev isar_generator build_runner

import 'package:isar/isar.dart';

part 'user.g.dart';

@collection
class User {
  Id id = Isar.autoIncrement;

  @Index(type: IndexType.value, caseSensitive: false)
  late String name;

  late int age;
}

// Open
final dir = await getApplicationDocumentsDirectory();
final isar = await Isar.open([UserSchema], directory: dir.path);

// Write
await isar.writeTxn(() async {
  await isar.users.put(User()
    ..name = 'Việt'
    ..age = 25);
});

// Query
final youngUsers = await isar.users
    .filter()
    .ageLessThan(30)
    .sortByName()
    .findAll();

// Watch
isar.users.where().watch(fireImmediately: true).listen((users) {
  print('${users.length} users');
});

9. Offline-first pattern

class UserRepository {
  final Dio _api;
  final Box<User> _cache;

  UserRepository(this._api, this._cache);

  Stream<List<User>> watchUsers() async* {
    // 1. Emit cached ngay
    yield _cache.values.toList();

    // 2. Fetch fresh từ API
    try {
      final r = await _api.get('/users');
      final fresh = (r.data as List).map((j) => User.fromJson(j)).toList();

      // 3. Update cache
      await _cache.clear();
      for (final u in fresh) {
        await _cache.put(u.id, u);
      }

      // 4. Emit fresh
      yield fresh;
    } catch (_) {
      // Network fail — vẫn có cache đã yield ở step 1
    }
  }
}

10. Cache TTL pattern

class CachedData<T> {
  final T data;
  final DateTime savedAt;
  final Duration ttl;

  bool get isExpired => DateTime.now().difference(savedAt) > ttl;

  const CachedData({required this.data, required this.savedAt, required this.ttl});
}

// Use
final cached = box.get('users');
if (cached != null && !cached.isExpired) {
  return cached.data;
}
// else: fetch fresh

11. Decision framework

12. Bài tập

13. Quiz

14. Tổng kết

• ✅ Spectrum 6+ option storage local.
• ✅ SharedPreferences — primitive setting.
• ✅ SecureStorage — token, password (encrypted per platform).
• ✅ sqflite — SQL relational, migration qua onUpgrade.
• ✅ Drift — sqflite + codegen type-safe + Stream watch.
• ✅ Hive / Isar — NoSQL object DB. Isar modern hơn.
• ✅ Offline-first: cache trước, fetch sau, update UI khi có fresh.
• ✅ Cache TTL pattern.
• ✅ Decision framework theo data shape + use case.

15. Kết nối

• Ch 10: cache API response.
• Ch 6, 7: state mgmt quản lý loading từ cache.
• Ch 14: test repo với mock storage.