Shared preferences plugin

Wraps platform-specific persistent storage for simple data (NSUserDefaults on iOS and macOS, SharedPreferences on Android, etc.). Data may be persisted to disk asynchronously, and there is no guarantee that writes will be persisted to disk after returning, so this plugin must not be used for storing critical data.

Supported data types are int, double, bool, String and List<String>.

Usage

To use this plugin, add shared_preferences as a dependency in your pubspec.yaml file.

Examples

Here are small examples that show you how to use the API.

Write data

// Obtain shared preferences.
final SharedPreferences prefs = await SharedPreferences.getInstance();

// Save an integer value to 'counter' key.
await prefs.setInt('counter', 10);
// Save an boolean value to 'repeat' key.
await prefs.setBool('repeat', true);
// Save an double value to 'decimal' key.
await prefs.setDouble('decimal', 1.5);
// Save an String value to 'action' key.
await prefs.setString('action', 'Start');
// Save an list of strings to 'items' key.
await prefs.setStringList('items', <String>['Earth', 'Moon', 'Sun']);

Read data

// Try reading data from the 'counter' key. If it doesn't exist, returns null.
final int? counter = prefs.getInt('counter');
// Try reading data from the 'repeat' key. If it doesn't exist, returns null.
final bool? repeat = prefs.getBool('repeat');
// Try reading data from the 'decimal' key. If it doesn't exist, returns null.
final double? decimal = prefs.getDouble('decimal');
// Try reading data from the 'action' key. If it doesn't exist, returns null.
final String? action = prefs.getString('action');
// Try reading data from the 'items' key. If it doesn't exist, returns null.
final List<String>? items = prefs.getStringList('items');

Remove an entry

// Remove data for the 'counter' key.
await prefs.remove('counter');

Multiple instances

In order to make preference lookup via the get* methods synchronous, shared_preferences uses a cache on the Dart side, which is normally only updated by the set* methods. Usually this is an implementation detail that does not affect callers, but it can cause issues in a few cases:

• If you are using shared_preferences from multiple isolates, since each isolate has its own SharedPreferences singleton and cache.
• If you are using shared_preferences in multiple engine instances (including those created by plugins that create background contexts on mobile devices, such as firebase_messaging).
• If you are modifying the underlying system preference store through something other than the shared_preferences plugin, such as native code.

If you need to read a preference value that may have been changed by anything other than the SharedPreferences instance you are reading it from, you should call reload() on the instance before reading from it to update its cache with any external changes.

If this is problematic for your use case, you can thumbs up this issue to express interest in APIs that provide direct (asynchronous) access to the underlying preference store, and/or subscribe to it for updates.

Migration and Prefixes

By default, the SharedPreferences plugin will only read (and write) preferences that begin with the prefix flutter.. This is all handled internally by the plugin and does not require manually adding this prefix.

Alternatively, SharedPreferences can be configured to use any prefix by adding a call to setPrefix before any instances of SharedPreferences are instantiated. Calling setPrefix after an instance of SharedPreferences is created will fail. Setting the prefix to an empty string '' will allow access to all preferences created by any non-flutter versions of the app (for migrating from a native app to flutter).

If the prefix is set to a value such as '' that causes it to read values that were not originally stored by the SharedPreferences, initializing SharedPreferences may fail if any of the values are of types that are not supported by SharedPreferences.

If you decide to remove the prefix entirely, you can still access previously created preferences by manually adding the previous prefix flutter. to the beginning of the preference key.

If you have been using SharedPreferences with the default prefix but wish to change to a new prefix, you will need to transform your current preferences manually to add the new prefix otherwise the old preferences will be inaccessible.

Testing

In tests, you can replace the standard SharedPreferences implementation with a mock implementation with initial values. This implementation is in-memory only, and will not persist values to the usual preference store.

final Map<String, Object> values = <String, Object>{'counter': 1};
SharedPreferences.setMockInitialValues(values);

Storage location by platform