Flutter local storage

import 'package:shared_preferences/shared_preferences.dart';

// Save data
Future<void> saveData() async {
  final prefs = await SharedPreferences.getInstance();

  // Save string
  await prefs.setString('username', 'Zhang San');

  // Save integer
  await prefs.setInt('age', 25);

  // Save boolean
  await prefs.setBool('isLoggedIn', true);

  // Save list (JSON string)
  await prefs.setStringList('tags', ['flutter', 'dart']);
}

// Read data
Future<void> loadData() async {
  final prefs = await SharedPreferences.getInstance();

  final username = prefs.getString('username') ?? '';
  final age = prefs.getInt('age') ?? 0;
  final isLoggedIn = prefs.getBool('isLoggedIn') ?? false;
  final tags = prefs.getStringList('tags') ?? [];

  print('Username: $username');
  print('Age: $age');
  print('Logged in: $isLoggedIn');
  print('Tags: $tags');
}

// Delete data
Future<void> deleteData() async {
  final prefs = await SharedPreferences.getInstance();

  // Delete single
  await prefs.remove('username');

  // Delete all
  await prefs.clear();
}

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

// Get documents directory
Future<Directory> get _documentDirectory async {
  return await getApplicationDocumentsDirectory();
}

// Write file
Future<void> writeFile() async {
  final dir = await _documentDirectory;
  final file = File('${dir.path}/my_file.txt');

  // Write text
  await file.writeAsString('Hello Flutter!');

  // Write bytes
  final bytes = [72, 101, 108, 108, 111];  // "Hello"
  await file.writeAsBytes(bytes);
}

// Read file
Future<void> readFile() async {
  final dir = await _documentDirectory;
  final file = File('${dir.path}/my_file.txt');

  if (await file.exists()) {
    // Read text
    final content = await file.readAsString();
    print('File content: $content');

    // Read bytes
    final bytes = await file.readAsBytes();
    print('Bytes: $bytes');
  }
}

// JSON file storage
Future<void> saveJson() async {
  final dir = await _documentDirectory;
  final file = File('${dir.path}/data.json');

  final data = {
    'name': 'Zhang San',
    'age': 25,
    'skills': ['Flutter', 'Dart'],
  };

  // Use jsonEncode to save JSON
  await file.writeAsString(jsonEncode(data));
}

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

// Database helper class
class DatabaseHelper {
  static final DatabaseHelper instance = DatabaseHelper._init();
  static Database? _database;

  DatabaseHelper._init();

  Future<Database> get database async {
    if (_database != null) return _database!;
    _database = await _initDB('my_app.db');
    return _database!;
  }

  // Initialize database
  Future<Database> _initDB(String filePath) async {
    final dbPath = await getDatabasesPath();
    final path = join(dbPath, filePath);

    return await openDatabase(
      path,
      version: 1,
      onCreate: _createDB,
    );
  }

  // Create table
  Future<void> _createDB(Database db, int version) async {
    await db.execute('''
      CREATE TABLE users(
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        name TEXT NOT NULL,
        email TEXT NOT NULL,
        age INTEGER
      )
    ''');
  }

  // Insert data
  Future<int> insertUser(Map<String, dynamic> user) async {
    final db = await database;
    return await db.insert('users', user);
  }

  // Query all users
  Future<List<Map<String, dynamic>>> getAllUsers() async {
    final db = await database;
    return await db.query('users');
  }

  // Conditional query
  Future<List<Map<String, dynamic>>> getUserByName(String name) async {
    final db = await database;
    return await db.query(
      'users',
      where: 'name = ?',
      whereArgs: [name],
    );
  }

  // Update data
  Future<int> updateUser(int id, Map<String, dynamic> user) async {
    final db = await database;
    return await db.update(
      'users',
      user,
      where: 'id = ?',
      whereArgs: [id],
    );
  }

  // Delete data
  Future<int> deleteUser(int id) async {
    final db = await database;
    return await db.delete(
      'users',
      where: 'id = ?',
      whereArgs: [id],
    );
  }

  // Close database
  Future<void> close() async {
    final db = await database;
    db.close();
  }
}

// Usage example
Future<void> dbExample() async {
  final db = DatabaseHelper.instance;

  // Add user
  await db.insertUser({
    'name': 'Zhang San',
    'email': 'zhangsan@example.com',
    'age': 25,
  });

  // Query all
  final users = await db.getAllUsers();
  print('User list: $users');

  // Update user
  await db.updateUser(1, {'name': 'Li Si', 'age': 30});

  // Delete user
  await db.deleteUser(1);
}