DataStore

1. Giới thiệu

DataStore là giải pháp lưu trữ data thay thế SharedPreferences, an toàn với coroutines và Flow.

So sánh với SharedPreferences

Feature	SharedPreferences	DataStore
Async API	❌	✅
Main thread safe	❌	✅
Error handling	❌	✅
Type safety	❌	✅ (Proto)
Migration	❌	✅

2. Setup

build.gradle.kts

dependencies {
    implementation("androidx.datastore:datastore-preferences:1.1.1")
}

3. Preferences DataStore

Tạo DataStore

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

Định nghĩa Keys

object PreferencesKeys {
    val USERNAME = stringPreferencesKey("username")
    val AGE = intPreferencesKey("age")
    val IS_LOGGED_IN = booleanPreferencesKey("is_logged_in")
    val SCORE = floatPreferencesKey("score")
}

Đọc dữ liệu

class SettingsRepository(private val context: Context) {

    val usernameFlow: Flow<String> = context.dataStore.data
        .map { preferences ->
            preferences[PreferencesKeys.USERNAME] ?: ""
        }

    val settingsFlow: Flow<UserSettings> = context.dataStore.data
        .map { preferences ->
            UserSettings(
                username = preferences[PreferencesKeys.USERNAME] ?: "",
                age = preferences[PreferencesKeys.AGE] ?: 0,
                isLoggedIn = preferences[PreferencesKeys.IS_LOGGED_IN] ?: false
            )
        }
}

Ghi dữ liệu

suspend fun saveUsername(username: String) {
    context.dataStore.edit { preferences ->
        preferences[PreferencesKeys.USERNAME] = username
    }
}

suspend fun saveSettings(settings: UserSettings) {
    context.dataStore.edit { preferences ->
        preferences[PreferencesKeys.USERNAME] = settings.username
        preferences[PreferencesKeys.AGE] = settings.age
        preferences[PreferencesKeys.IS_LOGGED_IN] = settings.isLoggedIn
    }
}

4. Sử dụng với ViewModel

class SettingsViewModel(
    private val repository: SettingsRepository
) : ViewModel() {

    val settings: StateFlow<UserSettings> = repository.settingsFlow
        .stateIn(
            scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(5000),
            initialValue = UserSettings()
        )

    fun updateUsername(username: String) {
        viewModelScope.launch {
            repository.saveUsername(username)
        }
    }
}

5. Sử dụng với Compose

@Composable
fun SettingsScreen(viewModel: SettingsViewModel = viewModel()) {
    val settings by viewModel.settings.collectAsState()

    Column {
        Text("Username: ${settings.username}")

        var newUsername by remember { mutableStateOf("") }

        OutlinedTextField(
            value = newUsername,
            onValueChange = { newUsername = it },
            label = { Text("New Username") }
        )

        Button(onClick = { viewModel.updateUsername(newUsername) }) {
            Text("Save")
        }
    }
}

6. Error Handling

val settingsFlow: Flow<UserSettings> = context.dataStore.data
    .catch { exception ->
        if (exception is IOException) {
            emit(emptyPreferences())
        } else {
            throw exception
        }
    }
    .map { preferences ->
        UserSettings(...)
    }

7. Migration từ SharedPreferences

val Context.dataStore by preferencesDataStore(
    name = "settings",
    produceMigrations = { context ->
        listOf(SharedPreferencesMigration(context, "old_prefs_name"))
    }
)

8. Proto DataStore (Type-safe)

Setup

build.gradle.kts

plugins {
    id("com.google.protobuf") version "0.9.4"
}

dependencies {
    implementation("androidx.datastore:datastore:1.1.1")
    implementation("com.google.protobuf:protobuf-javalite:3.25.1")
}

Định nghĩa Proto

src/main/proto/settings.proto

syntax = "proto3";

message Settings {
    string username = 1;
    int32 age = 2;
    bool is_logged_in = 3;
}

Serializer

object SettingsSerializer : Serializer<Settings> {
    override val defaultValue: Settings = Settings.getDefaultInstance()

    override suspend fun readFrom(input: InputStream): Settings {
        return Settings.parseFrom(input)
    }

    override suspend fun writeTo(t: Settings, output: OutputStream) {
        t.writeTo(output)
    }
}

Sử dụng Proto DataStore

val Context.settingsDataStore: DataStore<Settings> by dataStore(
    fileName = "settings.pb",
    serializer = SettingsSerializer
)

// Read
val settingsFlow: Flow<Settings> = context.settingsDataStore.data

// Write
suspend fun updateUsername(username: String) {
    context.settingsDataStore.updateData { current ->
        current.toBuilder()
            .setUsername(username)
            .build()
    }
}

---

📝 Tóm tắt

Type	Use Case
Preferences DataStore	Key-value đơn giản
Proto DataStore	Type-safe, complex objects

API	Mô tả
dataStore.data	Flow of preferences
dataStore.edit {}	Modify data
map {}	Transform data
catch {}	Handle errors