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//Listen app theme mode (dark, light)
private val selectedThemeChannel: ConflatedBroadcastChannel<String> by lazy {
ConflatedBroadcastChannel<String>().also { channel ->
channel.trySend(selectedTheme)
}
}
private val changeListener = SharedPreferences.OnSharedPreferenceChangeListener { _, key ->
when (key) {
PREF_DARK_MODE_ENABLED -> selectedThemeChannel.trySend(selectedTheme)
}
}
val selectedThemeFlow: Flow<String>
get() = selectedThemeChannel.asFlow()
view raw old.kt hosted with ❤ by GitHub
//initialization with extension
private val dataStore: DataStore<Preferences> = context.dataStore
val selectedThemeFlow = dataStore.data
.map { it[stringPreferencesKey(name = "pref_dark_mode")] }
view raw new.kt hosted with ❤ by GitHub
Read/write single value using SharedPreferences
enum class Theme(val storageKey: String) {
LIGHT("light"),
DARK("dark"),
SYSTEM("system")
}
private const val PREF_DARK_MODE = "pref_dark_mode"
private val prefs: SharedPreferences = context.getSharedPreferences("PREFERENCES_NAME", Context.MODE_PRIVATE)
fun getTheme(): String = prefs.getString(PREF_DARK_MODE, SYSTEM.storageKey)
?: SYSTEM.storageKey
fun updateTheme(value: String) {
prefs.edit {
putString(PREF_DARK_MODE, value)
}
}
view raw gistfile1.kt hosted with ❤ by GitHub

Well, two functions it is not so bad, but we can try to merge this into single Property.

enum class Theme(val storageKey: String) {
LIGHT("light"),
DARK("dark"),
SYSTEM("system")
}
private const val PREF_DARK_MODE = "pref_dark_mode"
private val prefs: SharedPreferences = context.getSharedPreferences("PREFERENCES_NAME", Context.MODE_PRIVATE)
var theme: String
get() = prefs.getString(PREF_DARK_MODE, SYSTEM.storageKey) ?: SYSTEM.storageKey
set(value) {
prefs.edit {
putString(PREF_DARK_MODE, value)
}
}
view raw sharedpref.kt hosted with ❤ by GitHub

To make it fully clear and supportable we can use the Kotlin delegation feature. As we want to read and write simultaneously, ReadWritePropertywill suit our goal.

class StringPreference(
private val preferences: SharedPreferences,
private val name: String,
private val defaultValue: String
) : ReadWriteProperty<Any, String?> {
@WorkerThread
override fun getValue(thisRef: Any, property: KProperty<*>) =
preferences.getString(name, defaultValue) ?: defaultValue
override fun setValue(thisRef: Any, property: KProperty<*>, value: String?) {
preferences.edit {
putString(name, value)
}
}
}

Please take a look at the final compact version, where all logic is encapsulated inside the delegate.

enum class Theme(val storageKey: String) {
LIGHT("light"),
DARK("dark"),
SYSTEM("system")
}
private val prefs: SharedPreferences =
context.getSharedPreferences("PREFERENCES_NAME", Context.MODE_PRIVATE)
var theme by StringPreference(
preferences = prefs,
name = "pref_dark_mode",
defaultValue = SYSTEM.storageKey
)
view raw Delegate.kt hosted with ❤ by GitHub
DataStore Preferences and missing API
val EXAMPLE_COUNTER = intPreferencesKey("example_counter")
val exampleCounterFlow: Flow<Int> = context.dataStore.data
.map { preferences ->
// No type safety.
preferences[EXAMPLE_COUNTER] ?: 0
}
view raw sample.kt hosted with ❤ by GitHub
Example from Documentation

Let’s make a small crutch
fun <T> DataStore<Preferences>.get(
key: Preferences.Key<T>,
defaultValue: T
): T = runBlocking {
data.first()[key] ?: defaultValue
}
fun <T> DataStore<Preferences>.set(
key: Preferences.Key<T>,
value: T?
) = runBlocking<Unit> {
edit {
if (value == null) {
it.remove(key)
} else {
it[key] = value
}
}
}
view raw extension.kt hosted with ❤ by GitHub

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Now let’s wrap this functionality into old delegates, replace SharedPreferences with DataStore and change the key.

class PreferenceDataStore<T>(
private val dataStore: DataStore<Preferences>,
private val key: Preferences.Key<T>,
private val defaultValue: T
) : ReadWriteProperty<Any, T> {
@WorkerThread
override fun getValue(thisRef: Any, property: KProperty<*>) =
dataStore.get(key = key, defaultValue = defaultValue)
override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
dataStore.set(key = key, value = value)
}
}
view raw new.kt hosted with ❤ by GitHub
enum class Theme(val storageKey: String) {
LIGHT("light"),
DARK("dark"),
SYSTEM("system")
}
// initialization DataStore with extension
private val dataStore: DataStore<Preferences> = context.dataStore
var selectedTheme by PreferenceDataStore<String>(
dataStore = dataStore,
key = stringPreferencesKey(name = "pref_dark_mode"),
defaultValue = SYSTEM.storageKey
)
view raw new.kt hosted with ❤ by GitHub

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