Level 13

Storing Preferences (DataStore)

DataStore over SharedPreferences

`SharedPreferences` is synchronous and error-prone. `DataStore` is the modern replacement: it is async, transactional, and exposes settings as a `Flow`. Perfect for things like theme choice or onboarding flags.

📚 Explanation

`preferencesDataStore` creates a single, type-safe key/value store backed by a coroutine `Flow`. Reads never block the main thread and automatically re-emit when a value changes. Writes go through `edit { }`, which is transactional — concurrent updates are serialized safely. This makes DataStore a drop-in, leak-free upgrade over `SharedPreferences` for app settings.

Note: Code execution is not available for Android/Kotlin in the browser. Use Android Studio to run and test the app.

kotlin

import androidx.datastore.core.DataStore
import androidx.datastore.preferences.core.*
import androidx.datastore.preferences.preferencesDataStore
import android.content.Context
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.map

// Define a single DataStore instance for the app
val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "settings")

class SettingsRepository(private val context: Context) {

    private object Keys {
        val DARK_MODE = booleanPreferencesKey("dark_mode")
    }

    // Read: exposed as a Flow that emits on every write
    val darkMode: Flow<Boolean> = context.dataStore.data
        .map { prefs -> prefs[Keys.DARK_MODE] ?: false }

    // Write: suspending + transactional
    suspend fun setDarkMode(enabled: Boolean) {
        context.dataStore.edit { prefs ->
            prefs[Keys.DARK_MODE] = enabled
        }
    }
}

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Storing Preferences (DataStore)

DataStore over SharedPreferences

📚 Explanation

Note: Code execution is not available for Android/Kotlin in the browser. Use Android Studio to run and test the app.

import androidx.datastore.core.DataStore

import androidx.datastore.preferences.core.*

import androidx.datastore.preferences.preferencesDataStore

import android.content.Context

import kotlinx.coroutines.flow.Flow

import kotlinx.coroutines.flow.map

// Define a single DataStore instance for the app

val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "settings")

class SettingsRepository(private val context: Context) {

private object Keys {

val DARK_MODE = booleanPreferencesKey("dark_mode")

}

// Read: exposed as a Flow that emits on every write

val darkMode: Flow<Boolean> = context.dataStore.data

.map { prefs -> prefs[Keys.DARK_MODE] ?: false }

// Write: suspending + transactional

suspend fun setDarkMode(enabled: Boolean) {

context.dataStore.edit { prefs ->

prefs[Keys.DARK_MODE] = enabled

}