SharedPreferences / DataStore in Android Kotlin

Introduction

We use SharedPreferences or DataStore to save small pieces of information on your phone. This helps your app remember things like settings or user choices even after closing.

Saving user preferences like theme or language choice.

Remembering if the user is logged in or not.

Storing simple flags like if a tutorial was shown.

Keeping small counters or scores in a game.

Saving last opened screen or app state.

Syntax

Android Kotlin

val sharedPref = context.getSharedPreferences("prefs", Context.MODE_PRIVATE)

// To save data
sharedPref.edit().putString("key", "value").apply()

// To read data
val value = sharedPref.getString("key", "default")

SharedPreferences stores data as key-value pairs.

Use apply() to save changes asynchronously.

Examples

Save a boolean value to remember if user is logged in.

Android Kotlin

sharedPref.edit().putBoolean("isLoggedIn", true).apply()

Read the boolean value, default is false if not set.

Android Kotlin

val isLoggedIn = sharedPref.getBoolean("isLoggedIn", false)

Create a DataStore instance for storing preferences.

Android Kotlin

val dataStore = context.createDataStore(name = "settings")

Save a string value in DataStore using a key.

Android Kotlin

val EXAMPLE_KEY = preferencesKey<String>("example_key")

runBlocking {
  dataStore.edit { settings ->
    settings[EXAMPLE_KEY] = "Hello"
  }
}

Sample App

This simple app saves a username "Alice" in SharedPreferences and then reads it back. It prints a welcome message with the saved name.

Android Kotlin

import android.content.Context
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    val sharedPref = getSharedPreferences("myPrefs", Context.MODE_PRIVATE)

    // Save a value
    sharedPref.edit().putString("username", "Alice").apply()

    // Read the value
    val username = sharedPref.getString("username", "Guest")

    println("Welcome, $username")
  }
}

Important Notes

SharedPreferences is simple but not suited for large or complex data.

DataStore is a newer, safer alternative that uses Kotlin coroutines.

Always use keys carefully to avoid overwriting data.

Summary

SharedPreferences and DataStore save small data on device.

Use key-value pairs to store and retrieve data.

DataStore is recommended for modern apps using Kotlin.