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Learn how to keep your data persistent in Flutter using ChangeNotifierProxyProvider without losing important information, even after updates.
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How to Persist Data with ChangeNotifierProxyProvider in Flutter

When developing applications using Flutter, managing state effectively is crucial for ensuring smooth user experiences. One common challenge developers face is how to maintain data consistency between related objects when one of them is updated. In this guide, we address this issue specifically in the context of persisting data when using ChangeNotifierProxyProvider. We’ll walk you through the problem, provide a clear solution, and ensure your data remains consistent after updates.

Setting the Scene: The Problem

Consider you have a Person provider and a Job provider in your Flutter application. The Job provider depends on the data from the Person provider. Here’s the challenge: when you update the age of Person, you notice that the career information in the Job provider resets to its initial state. This unintended data loss occurs due to the way the Job provider is being updated.

Here’s a quick overview of the Person and Job classes:

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The key problem arises from how we manage the Job provider in the main() function.

The Problematic Provider Initialization

In the main() function, you initialize both Person and Job as follows:

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

In the update method, the Job object is being created anew every time, which means it doesn’t retain its previous career value. As you discovered, when you update the age of Person, it results in the Job provider being reinitialized, and you lose your career information.

The Solution: Modify the Update Method

To resolve this issue, we need to persist the career value inside the Job provider when the Person provider is updated. This can be accomplished by modifying the update method to utilize the existing Job instance rather than creating a new one.

Change your update method to look like this:

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

Adding the setPerson Method

To support the modified update function, you'll need to add asetPerson method in the Job class that allows you to update the Person instance without losing the career information.

Here’s how you can implement the setPerson method in the Job class:

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

Conclusion

By implementing the changes outlined above, you can ensure that your Job provider retains its career data even when the age of the Person provider is updated. This allows for a more seamless and persistent state management experience in your Flutter application.

To summarize:

Use the existing Job instance in the update method of ChangeNotifierProxyProvider.

Create a setPerson method in the Job class to modify the associated Person without losing existing data.

With this approach, your app will deliver a more reliable and consistent user experience. Happy coding!