Shared Preferences: Providing a Persistent Store for Simple Data | Flutter Package

Disclaimer: This blog post assumes you have a basic understanding of Dart and Flutter.

Introduction

When developing mobile applications, it's common to encounter situations where you need to store and retrieve simple data persistently. Whether it's user preferences, settings, or application state, having a reliable and efficient way to store this information is crucial. That's where the shared_preferences package comes in handy. In this blog post, we will explore the capabilities of shared_preferences and learn how to utilize it in your Flutter projects.

What are Shared Preferences?

Shared_preferences is a Flutter plugin that allows you to store key-value pairs on the device's disk. It provides a persistent store for simple data, making it perfect for storing lightweight information such as user preferences and settings. The key-value pairs are stored as a file in the application's data directory, ensuring that the data persists even when the application is closed or the device is restarted.

Installation

Before we dive into the details of using shared_preferences, let's first install the package in our Flutter project. Open your project's pubspec.yaml file and add the following line under the dependencies section:

dependencies:
  shared_preferences: ^2.0.0

Save the file and run flutter pub get to fetch the package and its dependencies.

Usage

Using shared_preferences is incredibly simple. Let's say we want to store the user's preferred theme color in our application. We can achieve this in just a few steps:

1. Import the package:

import 'package:shared_preferences/shared_preferences.dart';

2. Create an instance of SharedPreferences:

SharedPreferences prefs = await SharedPreferences.getInstance();

3. Store the user's preferred theme color:

Color themeColor = Colors.blue;
prefs.setInt('themeColor', themeColor.value);

4. Retrieve the stored theme color:

Color storedThemeColor = Color(prefs.getInt('themeColor') ?? Colors.blue.value);

In the above code, we first obtain an instance of SharedPreferences using the getInstance() method. Once we have the instance, we can store the theme color using the setInt() method, providing a key and the color value. Later, we can retrieve the stored color using the getInt() method, providing the same key. We also provide a default value in case the stored value is null.

Supported Data Types

The shared_preferences package supports various data types, including:

• bool
• int
• double
• String
• List<String>
• List<int>
• List<double>

This allows you to store a wide range of information, from simple boolean flags to complex lists of data. For example, you can store an array of user preferences or a list of favorite items.

Additional Methods

Aside from the basic set and get methods, the shared_preferences package provides additional functionality:

• contains(key): Checks if a given key exists in the preferences.
• remove(key): Removes the key and its associated value from the preferences.
• clear(): Clears all the preferences, removing all key-value pairs.
• getKeys(): Retrieves a list of all the keys in the preferences.

These methods give you flexibility in managing the stored preferences and allow you to perform operations such as checking for the existence of a key, removing specific preferences, or clearing all preferences when needed.

Usage Scenarios

The shared_preferences package can be used in various scenarios to enhance the user experience of your Flutter applications. Let's explore a few examples:

1. User Preferences: You can use shared_preferences to store user preferences such as language selection, font size, or notification settings. This allows users to customize the app to their liking and have their preferences persist across app sessions.
2. Application Settings: Storing application-wide settings like dark mode, sound effects, or app-specific configurations becomes effortless with shared_preferences. Users can toggle these settings, and the app can remember their choices.
3. User Authentication: After a user logs in, you can store their authentication token or session details using shared_preferences. This ensures that users remain logged in even if they close and reopen the app.
4. User Onboarding: If your app has an onboarding process or tutorial, you can store a flag in shared_preferences to indicate whether the user has already completed it. This way, users won't be prompted to go through the onboarding process repeatedly.

Best Practices

While shared_preferences is a convenient tool for storing simple data, it's essential to keep a few best practices in mind:

• Secure Sensitive Information: Avoid storing sensitive information such as passwords, API keys, or personal data using shared_preferences. For secure storage of sensitive data, consider using more robust encryption techniques.
• Handle Null Values: When retrieving data from shared_preferences, make sure to handle null values appropriately. You can provide default values or implement fallback logic to ensure that your app doesn't crash or behave unexpectedly.
• Limit Data Size: Since shared_preferences stores data on the device's disk, it's important to be mindful of the data size. Avoid storing large amounts of data, as it can impact the performance of your app. If you need to store complex or large datasets, consider using other storage solutions such as a local database.

Conclusion

The shared_preferences package provides a straightforward and efficient way to store and retrieve simple data persistently in your Flutter applications. Whether you need to store user preferences, application settings, or any other lightweight data, shared_preferences has got you covered. Its ease of use and versatility make it a valuable tool in your Flutter development arsenal.