DataStore trong Android

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