Local Storage & Databases

Local Storage & Databases

Mobile apps need to persist data locally for offline access and user experience. Let's explore the different storage options available in mobile development.

Storage Options

  ┌─────────────────────────────────────────────────┐
  │         Local Storage Options                   │
  ├─────────────────────────────────────────────────┤
  │                                                  │
  │  Key-Value Storage                              │
  │  ┌──────────────────────────────────────┐       │
  │  │  AsyncStorage (RN) / SharedPreferences│      │
  │  │  Simple, small data, settings        │       │
  │  └──────────────────────────────────────┘       │
  │                                                  │
  │  SQLite Database                                │
  │  ┌──────────────────────────────────────┐       │
  │  │  SQLite / sqflite                    │       │
  │  │  Complex queries, structured data    │       │
  │  └──────────────────────────────────────┘       │
  │                                                  │
  │  File Storage                                   │
  │  ┌──────────────────────────────────────┐       │
  │  │  Documents, images, downloads        │       │
  │  └──────────────────────────────────────┘       │
  │                                                  │
  └─────────────────────────────────────────────────┘

React Native: AsyncStorage

import AsyncStorage from '@react-native-async-storage/async-storage';

// Save data
const saveUser = async (userData) => {
  try {
    await AsyncStorage.setItem('user', JSON.stringify(userData));
  } catch (error) {
    console.error('Error saving:', error);
  }
};

// Load data
const loadUser = async () => {
  try {
    const jsonValue = await AsyncStorage.getItem('user');
    return jsonValue != null ? JSON.parse(jsonValue) : null;
  } catch (error) {
    console.error('Error loading:', error);
  }
};

// Remove data
const removeUser = async () => {
  try {
    await AsyncStorage.removeItem('user');
  } catch (error) {
    console.error('Error removing:', error);
  }
};

Flutter: SharedPreferences & SQLite

import 'package:shared_preferences/shared_preferences.dart';

// Save simple data
Future<void> saveTheme(bool isDark) async {
  final prefs = await SharedPreferences.getInstance();
  await prefs.setBool('darkTheme', isDark);
}

// Load simple data
Future<bool> loadTheme() async {
  final prefs = await SharedPreferences.getInstance();
  return prefs.getBool('darkTheme') ?? false;
}

// SQLite for complex data
import 'package:sqflite/sqflite.dart';

Future<void> createDatabase() async {
  final db = await openDatabase(
    'my_app.db',
    version: 1,
    onCreate: (db, version) async {
      await db.execute('''
        CREATE TABLE users (
          id INTEGER PRIMARY KEY,
          name TEXT,
          email TEXT
        )
      ''');
    },
  );
}

When to Use What?

• Key-Value: Settings, user preferences, tokens
• SQLite: Complex data with relationships, offline-first apps
• File Storage: Images, documents, downloaded content