Shared Preferences in Flutter

What is Shared Preferences in Flutter?

Shared Preferences is a key-value storage mechanism that enables Flutter developers to store and retrieve data persistently on a device. It’s ideal for saving user preferences, configuration settings, or any lightweight data that needs to persist between app sessions.

Benefits of Using Shared Preferences

Persistent Storage: Data stored using Shared Preferences remains available even after the app is closed.
Lightweight: Best suited for small, simple datasets like user preferences or flags.
Ease of Use: Provides a simple API for storing and retrieving data.
Cross-Platform: Works seamlessly across Android and iOS.

Key Features of Shared Preferences

Key-Value Pair Storage: Data is stored as a pair where each key corresponds to a specific value.
Primitive Data Types: Supports basic types like int, double, bool, String, and List<String>.
Asynchronous Access: Uses asynchronous APIs to prevent UI blocking during read/write operations.

How to Use Shared Preferences in Flutter

1. Add the Dependency

To use Shared Preferences, include the plugin in your pubspec.yaml file:

dependencies:  
  shared_preferences: ^2.1.0

Run flutter pub get to install the package.

2. Import the Package

In your Dart file, import the shared_preferences library:

import 'package:shared_preferences/shared_preferences.dart';

3. Save Data

To save data, use the set methods available for each data type:

Future<void> saveData() async {  
  final prefs = await SharedPreferences.getInstance();  
  await prefs.setString('username', 'JohnDoe');  
  await prefs.setInt('age', 25);  
  await prefs.setBool('isLoggedIn', true);  
}

4. Retrieve Data

To retrieve data, use the get methods:

Future<void> retrieveData() async {  
  final prefs = await SharedPreferences.getInstance();  
  String? username = prefs.getString('username');  
  int? age = prefs.getInt('age');  
  bool? isLoggedIn = prefs.getBool('isLoggedIn');  

  print('Username: $username, Age: $age, Logged In: $isLoggedIn');  
}

5. Remove Data

To delete specific data, use the remove method:

Future<void> removeData() async {  
  final prefs = await SharedPreferences.getInstance();  
  await prefs.remove('username');  
}

6. Clear All Data

To clear all stored data, use the clear method:

Future<void> clearAllData() async {  
  final prefs = await SharedPreferences.getInstance();  
  await prefs.clear();  
}

Best Practices for Using Shared Preferences

Use for Small Data Only: Avoid using Shared Preferences for large datasets or complex data structures. For such cases, consider using a database like SQLite or Hive.
Secure Sensitive Data: Shared Preferences is not encrypted. Avoid storing sensitive information like passwords or API keys. Use secure storage plugins for such purposes.
Key Management: Use a consistent naming convention for keys to avoid conflicts. For example, prefix keys with the feature they belong to, like auth_isLoggedIn.
Error Handling: Always check for null values when retrieving data, as the key might not exist.

Common Use Cases for Shared Preferences

User Authentication State: Save whether a user is logged in.
App Themes: Store the user’s theme preference (dark/light mode).
Language Settings: Persist the selected language across app launches.
Introductory Screens: Track whether the user has seen the onboarding screens.

Limitations of Shared Preferences

No Encryption: Data is stored in plain text, making it unsuitable for sensitive information.
Limited Storage: Best suited for small data. Large datasets may slow down read/write operations.
No Complex Data: Supports only primitive data types, requiring serialization for custom objects.

Conclusion

Shared Preferences is a powerful tool in Flutter for handling lightweight persistent storage. With its simple API and cross-platform compatibility, it’s an excellent choice for saving app settings and user preferences. By following the best practices outlined in this guide, you can effectively leverage Shared Preferences to enhance your app’s user experience.

FAQs

Q1: Can I store complex objects in Shared Preferences?
No, Shared Preferences supports only primitive data types. However, you can serialize complex objects to JSON strings and store them as String.

Q2: Is Shared Preferences secure?
No, data stored in Shared Preferences is not encrypted. Use secure storage plugins like flutter_secure_storage for sensitive data.

Q3: What is the size limit for Shared Preferences?
There’s no explicit size limit, but it’s designed for small amounts of data. Storing large data can impact performance.

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