Shared Preferences in Flutter: Store and Retrieve data locally

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Store and retrieve data locallyFlutter is a popular framework for building cross-platform mobile applications. One of the essential features in mobile development is the ability to store data persistently across app sessions. Shared preferences in Flutter are one way to store and retrieve data in a key-value pair format. In this blog, we will explore what shared preferences are and how to use them in Flutter with examples.

What are Shared Preferences in Flutter?

Shared preferences are key-value pairs used to store and retrieve data in a Flutter application. They are often used to store simple user preferences, such as language settings, font size, or theme colors. Shared preferences are stored in the device’s file system and are persistent across app sessions.

Data once stored in shared preferences remain in the device's local storage, hence data can be retrieved whenever the app is launched. But Shared Preferences data is lost whenever the App Data is deleted or the App is uninstalled from the device.

Shared preferences are commonly used in Flutter applications because they are easy to use and provide a simple way to store and retrieve data. They are also lightweight and can store small amounts of data. Shared preferences data is stored in XML Format.

Shared Preferences supported data types

How to use Shared Preferences in Flutter

Shared preferences should be used only to store simple data like String, int, bool, etc, and NOT complex data like a dictionary / JSON / List of objects received from API.

To use Shared Preferences in Flutter, you need to add the following dependency to your pubspec.yaml file:

dependencies:
  shared_preferences: ^2.0.12

Then, run the command flutter packages get in your terminal to install the package.

Once you have added the shared_preferences package, you can use it in your Flutter application.

To store data in Shared Preferences, you need to follow these steps:

1. Get an instance of SharedPreferences
2. Store data in SharedPreferences
3. Retrieve data from SharedPreferences

Let’s go through each step with examples.

Step 1: Get an instance of SharedPreferences

To get an instance of SharedPreferences, you can use the getInstance() method from the SharedPreferences class. Here's an example:

import 'package:shared_preferences/shared_preferences.dart';

SharedPreferences preferences = await SharedPreferences.getInstance();

The await keyword is used to wait for the getInstance() method to complete before returning the SharedPreferences instance.

Step 2: Store data in SharedPreferences

To store data in SharedPreferences, you can use the set<Type>(key, value) method, where Type can be String, int, double, bool, or List<String>. Here's an example:

SharedPreferences preferences = await getSharedPreferencesInstance();

preferences.setString('username', 'johndoe');
preferences.setInt('age', 30);
preferences.setBool('isLogged', true);

In the example above, we store a String, an int, and a bool in SharedPreferences using the setString, setInt and setBool methods.

Step 3: Retrieve data from SharedPreferences

To retrieve data from SharedPreferences, you can use the get<Type>(key) method, where Type is the type of value you want to retrieve. Here's an example:

SharedPreferences preferences = await getSharedPreferencesInstance();

String username = preferences.getString('username');
int age = preferences.getInt('age');
bool isLogged = preferences.getBool('isLogged');

In the example above, we retrieve the String, int, and bool values we stored earlier using the getString, getInt and getBool methods.

Step 4: Delete data from SharedPreferences

To retrieve data from SharedPreferences, you can use the remove(key) method, where key is the name of the data you want to remove. Here's an example:

SharedPreferences preferences = await getSharedPreferencesInstance();

preferences.remove('username');
preferences.remove('age');
preferences.remove('isLogged');

Step 5: To Check whether a value is present or not?

containsKey used to check value is present or not.

SharedPreferences preferences = await getSharedPreferencesInstance();

bool checkValue = preferences.containsKey('age');

containsKey will give a boolean value, true for present and false for not present.

Conclusion

In this blog, we discussed how to use Shared Preferences in Flutter with examples. We learned how to get an instance of SharedPreferences, store retrieve and check if data exists in SharedPreferences. Shared Preferences is a simple and easy-to-use way to store and retrieve simple data in Flutter.

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