Flutter Shared Preferences: Storing Simple Data

In Flutter app development, you often need to store small amounts of data locally on the user's device. This could include user settings, preferences, or simple state information. For these use cases, Flutter provides the

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shared_preferences

package, which offers a simple key-value store mechanism.

What are Shared Preferences?

Shared Preferences is a Flutter plugin that allows you to save and retrieve primitive data types (like booleans, integers, doubles, strings, and string lists) in a persistent, asynchronous, and simple key-value store. It's built on top of native platform APIs (like

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SharedPreferences

on Android and

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NSUserDefaults

on iOS), making it efficient for small data storage.

Shared Preferences is ideal for storing user settings and simple data locally.

Think of Shared Preferences like a digital notebook where you can jot down small pieces of information, like whether a user has enabled dark mode or their username. Each piece of information is labeled with a unique 'key' so you can easily find it later.

The shared_preferences package acts as an abstraction layer over the native platform's key-value storage. On Android, this is typically SharedPreferences, and on iOS, it's NSUserDefaults. These native mechanisms are designed for storing small amounts of data efficiently. The Flutter plugin makes it cross-platform and easy to use within your Dart code.

Adding the `shared_preferences` Package

To use Shared Preferences, you first need to add the

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shared_preferences

package to your Flutter project. Open your

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pubspec.yaml

file and add the following under

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dependencies

yaml

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: ^2.2.2 # Use the latest version

After saving

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pubspec.yaml

, run

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flutter pub get

in your terminal to download and install the package.

Saving Data

To save data, you'll use the

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SharedPreferences

instance. You'll typically get an instance using

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SharedPreferences.getInstance()

. Then, you can use methods like

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setString()

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setInt()

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setBool()

, etc., providing a unique key and the value you want to store.

Imagine you want to save a user's name. You'd get an instance of SharedPreferences, then call setString('userName', 'Alice'). The setString method takes two arguments: the key (a unique string identifier, like 'userName') and the value (the string 'Alice' in this case). This operation is asynchronous, so you'll need to await it.

📚

Text-based content

Library pages focus on text content

Here's a code snippet for saving a boolean value (e.g., for a dark mode toggle):

dart

import 'package:shared_preferences/shared_preferences.dart';
Future saveDarkModePreference(bool isDarkMode) async {
  final prefs = await SharedPreferences.getInstance();
  await prefs.setBool('darkModeEnabled', isDarkMode);
}

Retrieving Data

To retrieve data, you use similar methods, but they are prefixed with

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get

(e.g.,

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getString()

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getInt()

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getBool()

). These methods also require the key you used when saving the data. Importantly, these methods return a

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Future

, so you'll need to

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await

them. If the key doesn't exist, they will return

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null

or a default value if you provide one.

Here's how you might retrieve the dark mode preference:

dart

import 'package:shared_preferences/shared_preferences.dart';
Future getDarkModePreference() async {
  final prefs = await SharedPreferences.getInstance();
  // Provide a default value if the key doesn't exist
  return prefs.getBool('darkModeEnabled') ?? false;
}

Removing Data

You can also remove specific key-value pairs using the

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remove()

method, or clear all stored data using

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clear()

Example of removing a specific preference:

dart

Future removeUserName() async {
  final prefs = await SharedPreferences.getInstance();
  await prefs.remove('userName');
}

Remember that Shared Preferences is designed for small amounts of data. For larger or more complex data structures, consider using other storage solutions like SQLite databases or file storage.

Use Cases for Shared Preferences

Shared Preferences are excellent for:

User Preferences: Storing themes (dark/light mode), language settings, notification preferences.
Session Management: Storing a boolean flag indicating if a user is logged in.
Simple State: Remembering the last viewed item or a user's input in a form.
Onboarding Status: Tracking if a user has completed the initial app tutorial.

Key Considerations

Always handle the

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Future

returned by

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SharedPreferences

methods using

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async

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await

. Provide default values when retrieving data to gracefully handle cases where a key might not exist yet. Be mindful of security; Shared Preferences are not encrypted and should not be used for sensitive data like passwords or API keys.

Learning Resources

Flutter Shared Preferences Package Documentation(documentation)

The official documentation for the shared_preferences plugin, detailing installation, usage, and available methods.

Flutter Docs: Working with Forms and User Input(documentation)

Learn how to handle user input in Flutter, which often involves saving preferences.

Flutter Shared Preferences Tutorial by Fireship(video)

A concise and engaging video tutorial explaining how to use shared preferences in Flutter.

Flutter Shared Preferences: Save and Load Data by The App Expert(video)

A step-by-step guide on implementing shared preferences for data persistence in Flutter applications.

Flutter Shared Preferences Example(blog)

A practical example demonstrating how to save and retrieve various data types using shared preferences in Flutter.

Flutter Shared Preferences: A Complete Guide(blog)

A comprehensive guide covering the basics, advanced usage, and best practices for shared preferences in Flutter.

Flutter State Management: Shared Preferences(blog)

Discusses shared preferences as a simple state management solution for small data in Flutter.

SharedPreferences (Android Developers)(documentation)

Understand the underlying Android mechanism that Flutter's shared_preferences plugin utilizes.

UserDefaults (Apple Developer Documentation)(documentation)

Explore the equivalent mechanism for storing preferences on iOS platforms.

Flutter Persistence Options(documentation)

An overview of different data persistence strategies in Flutter, placing shared preferences in context.

Shared Preferences for Simple Data

Flutter Shared Preferences: Storing Simple Data

What are Shared Preferences?

Shared Preferences is ideal for storing user settings and simple data locally.

Adding the `shared_preferences` Package

Saving Data

Retrieving Data

Removing Data

Use Cases for Shared Preferences

Key Considerations

Learning Resources