Fixing the Flutter Counter App: How to Properly Use Shared Preferences with Change Notifier

Learn how to resolve issues in your Flutter app with Shared Preferences and Change Notifier, ensuring the counter retains its value when reopened.
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This video is based on the question https://stackoverflow.com/q/63763206/ asked by the user 'kosaku' ( https://stackoverflow.com/u/14219281/ ) and on the answer https://stackoverflow.com/a/63763300/ provided by the user 'Scott Godfrey' ( https://stackoverflow.com/u/1272655/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fixing the Flutter Counter App: How to Properly Use Shared Preferences with Change Notifier

If you've dabbled in Flutter for building mobile applications, you might have experimented with SharedPreferences to persist data across app sessions. However, you may have encountered challenges when trying to store a counter value that remains consistent even after your app restarts. This guide will address a common issue related to using Change Notifier in conjunction with Shared Preferences and how you can solve it effectively.

The Problem

In a typical counter application, one typically expects the application to display the last counter value when reopened. However, in this case, users found that the counter resets to zero upon launching the app, only updating correctly after tapping the add button. The key questions are:

Why is the counter not saving correctly when the application closes?

How can we resolve this issue to ensure the last counter value appears when the app is reopened?

Analyzing the Code

Here is the critical part of the code that needs our attention:

[[See Video to Reveal this Text or Code Snippet]]

Identifying Key Issues

Lack of Getter for Counter:

The method getCounter() is being used in the widget but does not return the counter value correctly as it has asynchronous behavior due to _getPrefItems(). This needs correction.

No Notifications:

While using ChangeNotifier, it is crucial to call notifyListeners() to update the UI when the underlying data changes. This isn't called upon fetching the value from SharedPreferences.

Proposed Solutions

To resolve these issues, follow the steps below:

1. Updating the Counter Getter and Fetching Logic

We need to improve how the counter value is fetched to ensure that it always provides the latest value to the UI. The following adjustments can be made in the MyHomePageModel class:

[[See Video to Reveal this Text or Code Snippet]]

2. Updating Widget to Use the Getter

Now, we need to update the widget to use the getter instead of the method:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

By making the changes above, your Flutter counter app should now work as intended. The app will show the last counter value when it opens and seamlessly increment it upon tapping the add button. Using Shared Preferences effectively alongside Change Notifier ensures that the user experiences a consistent and reliable application.

Now, give your Flutter app a test run and see how these adjustments have improved its functionality. Happy coding!