Shared Preferences สำหรับข้อมูล

When building mobile apps, you often need to store small bits of data locally on the device. This could be anything from a user's dark mode preference to their last logged-in status.

shared_preferences is a Flutter package that helps you do just that! It provides a simple way to store key-value pairs of primitive data types.

• Simple Data: Ideal for storing simple data types like booleans, integers, doubles, strings, and lists of strings.
• User Settings: Perfect for saving user preferences, app settings, or theme choices.
• Lightweight: It's a quick and easy way to persist small amounts of data without needing a full database.

Think of it like a small digital notepad for your app's temporary memory!

To use shared_preferences, you first need to add it to your project's dependencies.

Open your pubspec.yaml file and add the following line under dependencies:

Once the package is added, you can start saving data. You'll need to get an instance of SharedPreferences and then use methods like setBool(), setString(), etc.

Remember to use await because these operations are asynchronous!

Try running this example to see how a boolean value is saved. We'll set a 'welcomeShown' flag to true.

To get data back, you use corresponding get methods like getBool(), getString(), etc. These methods return a nullable type (e.g., bool?) because the key might not exist.

It's good practice to provide a default value using the ?? operator if the key is not found.

Let's load the welcomeShown preference we saved earlier. Notice how we handle the case where it might not exist by providing a default of false.

shared_preferences supports several basic data types:

• setString(key, value) for text
• setInt(key, value) for whole numbers
• setDouble(key, value) for decimal numbers
• setStringList(key, value) for lists of strings

There are corresponding get methods for each type.

This example demonstrates saving and loading a string, an integer, and a list of strings. See how different types are handled.

You can also remove stored preferences:

• remove(key): Deletes a specific key-value pair.
• clear(): Deletes ALL data stored by your app using shared_preferences. Use with caution!

Both methods are asynchronous and return a Future<bool> indicating success.

You want to store a user's preferred language, which is a single string like 'en_US' or 'es_ES'. Which shared_preferences method is the most appropriate for saving this data?

Great job! You've learned how to use shared_preferences to store and retrieve small, simple data locally in your Flutter applications.

• It's ideal for user settings and preferences.
• Supports basic types: bool, int, double, string, and List<String>.
• Operations are asynchronous (use await).
• Remember to handle null values when retrieving data.

Next, you'll explore more structured data storage with SQLite databases!