Скачать или смотреть Understanding shared_preferences Persistence in Flutter Apps

Explore how `shared_preferences` in Flutter works, why data might not persist after app closure, and how to handle user authentication effectively.
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Understanding shared_preferences Persistence in Flutter Apps

When developing an app in Flutter, you might come across a situation where you need to store user data locally. The shared_preferences package is a popular tool for this purpose, allowing you to save key-value pairs in a persistent storage. However, you've probably noticed the cautionary note in the documentation: “Data may be persisted to disk asynchronously, and there is no guarantee that writes will be persisted to disk after returning.” This raises a critical question: Will the data stored using shared_preferences persist after the app is killed?

The Question at Hand

You've logged into your app and want to ensure that users remain logged in even if they kill the app and reopen it later. This brings up your concern about whether the data stored using shared_preferences will be deleted when the app is closed. Given the documentation's cautious wording, this is a valid worry.

Understanding Data Persistence

Normal Behavior of shared_preferences

Data Retention: Under normal circumstances, anytime data is saved using shared_preferences, it is retained unless explicitly deleted or if the app is uninstalled.

User Actions: Users have the ability to clear app data through their phone settings, which can cause loss of stored preferences. This includes scenarios where users clear the cache or reset the app.

Key Considerations

Asynchronous Data Writing: The statement from the documentation indicates that data writing is done asynchronously. This means the app might not finish the write process before the user closes it. Having this in mind, it’s essential to properly handle data storage to ensure that important data is saved correctly.

Non-Critical Data: According to the documentation, shared_preferences should not be used for storing critical data. For sensitive or essential data, consider using encrypted storage solutions or other secure storage methods.

Solution: Keeping Users Logged In

To ensure users remain logged in after closing and reopening the app, you can implement the following practices with shared_preferences:

Implement Login Logic:

After successful login, save user credentials (like tokens or user IDs) to shared_preferences.

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Check Session on Launch:

Upon app startup, check if user credentials exist in shared_preferences. If they do, you can automatically log the user in without requiring them to input their credentials again.

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Provide User Feedback:

Make sure to inform the user that they can manage their settings or clear data, which may affect their session persistence.

Conclusion

While shared_preferences provides a simple way to store user settings and credentials in your Flutter app, it’s essential to understand its limitations. Data is not guaranteed to be available after an app closure due to user actions or asynchronous write operations. Therefore, always prepare for scenarios where data might be lost, and ensure that you have sufficient checks in place to provide a seamless user experience.

By taking the precautions outlined above, you can confidently keep users logged in and improve overall user retention for your app.