What are SharedPreferences in Flutter?
SharedPreferences is a simple key–value storage used to persist small amounts of data on the device. It is intended for storing application preferences, not business data or sensitive information.
Typical use cases include theme selection, language choice, onboarding flags, or feature toggles.
Why does it matter in Flutter app development?
SharedPreferences solves a very common problem in mobile apps: remembering simple settings between launches.
It is lightweight, easy to configure, and works consistently across platforms, which makes it a common choice for entry-level persistence in Flutter projects.
How does it work?
It acts as a persistent in-memory cache backed by a physical file. On initialization, it reads the entire XML file (Android) or plist (iOS) from disk into RAM. All subsequent reads happen synchronously from memory (instant access), while writes are committed asynchronously to disk to prevent blocking the UI thread. This architecture means it is not a database query engine, but a state synchronization mechanism for flat files.
How to use SharedPreferences in Flutter?
final prefs = await SharedPreferences.getInstance();
await prefs.setBool('isDarkMode', true);
final isDarkMode = prefs.getBool('isDarkMode') ?? false;
Writes are asynchronous.
Reads are synchronous after initialization.
Common mistakes to avoid
- Storing sensitive data: A critical mistake is storing sensitive data such as passwords, access tokens, or personal information. On Android, these values are readable from an XML file. Sensitive data should always be stored using
flutter_secure_storage. - Treating it like a database: All values are loaded into RAM at startup, so storing large JSON objects or long lists can slow down application launch.
- Storing entire objects: Beginners also often try to store entire objects.
SharedPreferences does not support custom types, so objects must be serialized (for example to JSON) and stored as strings.
When to use SharedPreferences?
SharedPreferences is ideal for storing small, simple pieces of data that represent user or application preferences rather than core business information. This includes settings like theme mode (light/dark), onboarding completion flags, last visited screens, or user-selected language. Because SharedPreferences provides a key-value storage API, it is easy to read and write values using a simple, efficient API, which makes it convenient for persisting lightweight state across app launches.
It is particularly useful when persistence needs are minimal and do not justify introducing a full local database. For instance, saving a toggle state in settings or remembering whether a tutorial has been completed are perfect use cases. SharedPreferences is cross-platform and integrates seamlessly with Flutter, requiring minimal setup while offering reliable storage for small datasets.
When not to use SharedPreferences?
SharedPreferences should not be used for complex, structured, or sensitive data. Large datasets, such as product catalogs, user-generated content, or transaction histories, can quickly become unmanageable and lead to performance issues. Similarly, storing sensitive information like passwords or authentication tokens directly in SharedPreferences is insecure—developers should instead use secure storage solutions that encrypt data at rest.
Additionally, SharedPreferences is unsuitable when relationships between data objects or querying capabilities are required. For example, if you need to filter, sort, or join collections of records, a proper local database such as Hive, Drift, or Isar is far more appropriate. Using SharedPreferences in these cases can lead to brittle, hard-to-maintain code and increased risk of data corruption.
