Скачать или смотреть Saving a List of Objects to Local Memory in Flutter Using Shared Preferences

Learn how to effectively utilize `shared_preferences` package in Flutter to save and retrieve a list of objects. This guide breaks down the process for ease of understanding.
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This video is based on the question https://stackoverflow.com/q/65359242/ asked by the user 'Punreach Rany' ( https://stackoverflow.com/u/13942929/ ) and on the answer https://stackoverflow.com/a/65362997/ provided by the user 'Stefano Amorelli' ( https://stackoverflow.com/u/9367299/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Saving a List of Objects to Local Memory in Flutter Using Shared Preferences

When developing applications with Flutter, one common requirement is to save data locally on the device. This is especially pertinent when you want to store a collection of objects, like a list of persons in your app. In this post, we'll walk through how to effectively save and retrieve a list of Person objects using the shared_preferences package.

Understanding the Problem

Let's say we have a custom class named Person, which holds some basic attributes such as name, age, and gender. You might want to save a list of these Person objects to local memory, so that they can be retrieved later even if the app is closed. How can we achieve this in a Flutter application?

Here’s what our Person class looks like:

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The Solution

Storing a list of complex objects (like instances of Person) in local storage requires a slight modification of our approach. Since shared_preferences can only store primitive types, we need to convert our list of objects into a format that can be saved easily. One of the most efficient ways to do this is by using JSON encoding.

Step 1: Modifying the Person Class

In order to convert the Person objects to JSON and back, we need to add two methods: a constructor for mapping from JSON and a method to convert to JSON. Here's how you can enhance your Person class:

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Step 2: Saving the List

To save the list of Person objects, we will first convert each Person object to JSON and then store it as a String list in shared_preferences. Below is the function you will use for this:

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Step 3: Retrieving the List

Now, to retrieve the list of Person objects, you'll fetch the stored list from shared_preferences, decode each JSON string back into a Person object, and return the list. Here’s how you do it:

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Summary

In this guide, we addressed how to save and retrieve a list of objects in Flutter using shared_preferences. By modifying the Person class to include JSON serialization methods and using these methods to store and retrieve data, we’ve provided an efficient way to manage local data.

Key Takeaways:

Use jsonEncode to convert objects to strings.

Use jsonDecode to convert strings back to objects.

Always check for null or empty lists when fetching data from shared_preferences.

By following these steps, you can easily manage lists of complex objects in your Flutter applications. Happy coding!