Contents
Outline
WHen we develop the app in Flutter, like the web localStorage or React Native AsyncStorage, we want to store the simple data to the user device. At this time, we can use the Shared preferences package in Flutter.
You can see details about how to use the Shared preferences on the Flutter official document.
- Official document: Store key-value data on disk
Install Shared preferences package
The Shared preferences package helps us to simply store data in the form of key-value on the user device. To use the Shared preferences package, execute the command below to install it.
flutter pub add shared_preferences
How to use Shared preferences
We can store int, double, bool, string and List<String> data by Shared preferences. Let’s see how to create/read/delete the data by Shared preferences.
Store data
You can store the data by Shared preferences like the below.
...
import 'package:shared_preferences/shared_preferences.dart';
...
final prefs = await SharedPreferences.getInstance();
prefs.setInt('counter', 0);
prefs.setDouble('width', 20.5);
prefs.setBool('isAdmin', true);
prefs.setString('userName', 'dev-yakuza');
prefs.setStringList('alphabet', ['a', 'b', 'c', 'd']);
Read data
You can read the data by Shared preferences like the below.
...
import 'package:shared_preferences/shared_preferences.dart';
...
final prefs = await SharedPreferences.getInstance();
final counter = prefs.getInt('counter') ?? 0;
final width = prefs.getDouble('width') ?? 10.5;
final isAdmin = prefs.getBool('isAdmin') ?? false;
final userName = prefs.getString('userName') ?? '';
final alphabet = prefs.getStringList('alphabet') ?? [];
final data = prefs.get('userInfo') : {};
Delete data
You can delete the data by Shared preferences like the below.
...
import 'package:shared_preferences/shared_preferences.dart';
...
final prefs = await SharedPreferences.getInstance();
prefs.remove('counter');
Also, you can delete all data like the below.
prefs.clear();
Unit Test
When you do the unit test the widget which uses the Shared preferences package, you can use setMockInitialValues, that the Shared preferences package providers, to initialize data.
...
import 'package:shared_preferences/shared_preferences.dart';
...
setUp(() {
SharedPreferences.setMockInitialValues({});
});
Completed
Done! we’ve seen how to use the Shared preferences package to store/read/delete the simple data to the user device. the Shared preferences package is designed for the simple data, so it is not suitable for storing the large data. I recommend you to use the Shared preferences package to store the simple data like the settings option which the user selected.
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