Скачать или смотреть Resolving Flutter shared_preferences Not Storing Data

Are you struggling with Flutter's shared_preferences not storing data? Follow our structured guide to ensure your app saves data as intended!
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This video is based on the question https://stackoverflow.com/q/65359365/ asked by the user 'mvasco' ( https://stackoverflow.com/u/2665223/ ) and on the answer https://stackoverflow.com/a/65359761/ provided by the user 'Tim Klingeleers' ( https://stackoverflow.com/u/6192895/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue: Flutter's shared_preferences Not Storing Data

When working on a Flutter application, you may find that your app sometimes fails to properly store data using the shared_preferences package. This common issue can lead to confusion and frustration, especially if you're unsure of the root cause. In this post, we will explore this problem in detail and provide a clear solution to ensure that your data is stored correctly.

The Problem Explained

In the situation presented, the developer has implemented the shared_preferences package and is trying to save a Firebase token to persistent storage. However, despite the code appearing correct, the data retrieved from shared_preferences returns an empty string. This indicates that the saving process wasn’t executed correctly.

A Closer Look at the Code Implementation

Here’s a brief overview of the key components that are involved in the data storage process:

Shared Preferences Helper Class: This class (StorageUtil) is designed to manage interactions with shared_preferences.

Storing Data: The function _refreshToken() attempts to save a token retrieved from Firebase to shared preferences.

Retrieving Data: The attempt to read the token from shared preferences results in an empty string, indicating that the storing process might not have executed properly.

Let's review the relevant snippets of code for clarity:

StorageUtil Class Implementation

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

Code to Store Token in Shared Preferences

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Code to Retrieve Token

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The Solution: Properly Initializing Shared Preferences

The root cause of the issue is related to the initialization of the SharedPreferences instance. The key point here is that you need to ensure that the _init() method is called before you attempt to read or write any data.

Steps to Fix the Issue

To solve this problem, follow these simple steps:

Call the getInstance() Method: Ensure that you call await StorageUtil.getInstance() before you attempt to put or get data. This method initializes the _preferences property.

Here's the corrected version of the _refreshToken function:

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

Don’t Forget Retrieving the Token

Similarly, when you retrieve the token, make sure that you also invoke the getInstance() method:

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

Conclusion

By ensuring that your SharedPreferences instance is properly initialized before attempting to read or write data, you can resolve the issue of flutter shared_preferences not storing data. This approach will not only make your application more reliable but will also simplify your debugging process.

If you have any further questions or encounter other issues related to Flutter development, feel free to share your experiences! Happy coding!