What is SharedPreferences and how to use it?

SharedPreferences is a simple mechanism for storing small amounts of data in key-value pairs. It is ideal for saving user settings or small flags.

Usage:

1. Adding dependency: In the pubspec.yaml file, add:

   dependencies:
     flutter:
       sdk: flutter
     shared_preferences: ^2.2.0 # Use the latest version
   

   and run flutter pub get.

2. Import:

   import 'package:shared_preferences/shared_preferences.dart';
   

3. Getting an instance:

   // Asynchronous operation
   SharedPreferences prefs = await SharedPreferences.getInstance();
   

4. Writing data:

   // Write a string
   prefs.setString('username', 'Alice');
   // Write an integer
   prefs.setInt('age', 30);
   // Write a double
   prefs.setDouble('salary', 50000.50);
   // Write a boolean
   prefs.setBool('darkMode', true);
   // Write a list of strings
   prefs.setStringList('items', ['item1', 'item2']);
   

   All write methods return Future<bool>, indicating success.

5. Reading data:

   // Read a string
   String? username = prefs.getString('username'); // Returns null if key not found
   // Read an integer
   int? age = prefs.getInt('age');
   // Read a double
   double? salary = prefs.getDouble('salary');
   // Read a boolean
   bool? darkMode = prefs.getBool('darkMode');
   // Read a list of strings
   List<String>? items = prefs.getStringList('items');
   

6. Deleting data:

   // Remove by key
   prefs.remove('username'); // Returns Future<bool>
   // Clear all data
   prefs.clear(); // Returns Future<bool>
   

Limitations:

• Not suitable for storing large amounts of data or complex structures.
• Data is stored in plain text (though at the app level), not suitable for sensitive information.
• Works with basic data types. For objects, serialization/deserialization (e.g., with JSON) is required.