如何解决Kotlin 协程 Kotlin Flow 和共享首选项从不调用 awaitClose
我很想观察共同偏好的变化。以下是我使用 Kotlin Flow 的方法:
数据来源。
interface DataSource {
fun bestTime(): Flow<Long>
fun setBestTime(time: Long)
}
class LocalDataSource @Inject constructor(
@ActivityContext context: Context
) : DataSource {
private val preferences = context.getSharedPreferences(PREFS_FILE_NAME,Context.MODE_PRIVATE)
@ExperimentalCoroutinesApi
override fun bestTime() = callbackFlow {
trySendBlocking(preferences,PREF_KEY_BEST_TIME)
val listener = SharedPreferences.OnSharedPreferenceChangeListener { sharedPreferences,key ->
if (key == PREF_KEY_BEST_TIME) {
trySendBlocking(sharedPreferences,key)
}
}
preferences.registerOnSharedPreferenceChangeListener(listener)
awaitClose { // NEVER CALLED
preferences.unregisterOnSharedPreferenceChangeListener(listener)
}
}
@ExperimentalCoroutinesApi
private fun ProducerScope<Long>.trySendBlocking(
sharedPreferences: SharedPreferences,key: String?
) {
trySendBlocking(sharedPreferences.getLong(key,0L))
.onSuccess { }
.onFailure {
Log.e(TAG,"",it)
}
}
override fun setBestTime(time: Long) = preferences.edit {
putLong(PREF_KEY_BEST_TIME,time)
}
companion object {
private const val TAG = "LocalDataSource"
private const val PREFS_FILE_NAME = "PREFS_FILE_NAME"
private const val PREF_KEY_BEST_TIME = "PREF_KEY_BEST_TIME"
}
}
存储库
interface Repository {
fun observeBestTime(): Flow<Long>
fun setBestTime(bestTime: Long)
}
class RepositoryImpl @Inject constructor(
private val dataSource: DataSource
) : Repository {
override fun observeBestTime() = dataSource.bestTime()
override fun setBestTime(bestTime: Long) = dataSource.setBestTime(bestTime)
}
视图模型
class BestTimeViewModel @Inject constructor(
private val repository: Repository
) : ViewModel() {
// Backing property to avoid state updates from other classes
private val _uiState = MutableStateFlow(0L)
val uiState: StateFlow<Long> = _uiState
init {
viewModelScope.launch {
repository.observeBestTime()
.onCompletion { // CALLED WHEN THE SCREEN IS ROTATED OR HOME BUTTON PRESSED
Log.d("myTag","viewModelScope onCompletion")
}
.collect { bestTime ->
_uiState.value = bestTime
}
}
}
fun setBestTime(time: Long) = repository.setBestTime(time)
}
片段。
@AndroidEntryPoint
class MetaDataFragment : Fragment(R.layout.fragment_meta_data) {
@Inject
lateinit var timeFormatter: TimeFormatter
@Inject
lateinit var bestTimeViewModel: BestTimeViewModel
override fun onViewCreated(view: View,savedInstanceState: Bundle?) {
super.onViewCreated(view,savedInstanceState)
val bestTimeView = view.findViewById<TextView>(R.id.best_time_value)
// Create a new coroutine in the lifecycleScope
viewLifecycleOwner.lifecycleScope.launch {
// repeatOnLifecycle launches the block in a new coroutine every time the
// lifecycle is in the STARTED state (or above) and cancels it when it's STOPPED.
viewLifecycleOwner.repeatOnLifecycle(Lifecycle.State.STARTED) {
// Trigger the flow and start listening for values.
// This happens when lifecycle is STARTED and stops
// collecting when the lifecycle is STOPPED
bestTimeViewModel.uiState
.map { millis ->
timeFormatter.format(millis)
}
.onCompletion { // CALLED WHEN THE SCREEN IS ROTATED OR HOME BUTTON PRESSED
Log.d("MyApp","onCompletion")
}
.collect {
bestTimeView.text = it
}
}
}
}
}
我注意到从未调用过 awaitClose
。但这就是我的清理代码所在的地方。请指教。如果首先使用 callbackFlow
不是一个好主意,请告诉我(因为您可以看到一些函数是 ExperimentalCoroutinesApi
意味着它们的行为可以改变)
解决方法
问题是,您正在通过使用
注入您的 ViewModel,就好像它只是一个常规类一样@Inject
lateinit var bestTimeViewModel: BestTimeViewModel
因此,永远不会取消 ViewModel 的 viewModelScope
,因此永远收集 Flow。
根据 Documentation,您应该使用
privat val bestTimeViewModel: BestTimeViewModel by viewModels()
这可确保在您的 Fragment 销毁时调用 ViewModel 的 onCleared
方法,该方法将取消 viewModelScope
。
还要确保您的 ViewModel 使用 @HiltViewModel
进行注释:
@HiltViewModel
class BestTimeViewModel @Inject constructor(...) : ViewModel()
,
我找到了一个解决方案,可以让我保存一个简单的数据集(例如首选项)并使用 Kotlin Flow 观察其变化。它是Preferences DataStore
。
这是我使用的代码实验室和指南:
https://developer.android.com/codelabs/android-preferences-datastore#0
https://developer.android.com/topic/libraries/architecture/datastore
这是我的代码:
import android.content.Context
import androidx.datastore.preferences.core.edit
import androidx.datastore.preferences.core.emptyPreferences
import androidx.datastore.preferences.core.longPreferencesKey
import androidx.datastore.preferences.preferencesDataStore
import dagger.hilt.android.qualifiers.ApplicationContext
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.catch
import kotlinx.coroutines.flow.map
import java.io.IOException
data class UserPreferences(val bestTime: Long)
private const val USER_PREFERENCES_NAME = "user_preferences"
private val Context.dataStore by preferencesDataStore(
name = USER_PREFERENCES_NAME
)
interface DataSource {
fun userPreferencesFlow(): Flow<UserPreferences>
suspend fun updateBestTime(newBestTime: Long)
}
class LocalDataSource(
@ApplicationContext private val context: Context,) : DataSource {
override fun userPreferencesFlow(): Flow<UserPreferences> =
context.dataStore.data
.catch { exception ->
// dataStore.data throws an IOException when an error is encountered when reading data
if (exception is IOException) {
emit(emptyPreferences())
} else {
throw exception
}
}
.map { preferences ->
val bestTime = preferences[PreferencesKeys.BEST_TIME] ?: 0L
UserPreferences(bestTime)
}
override suspend fun updateBestTime(newBestTime: Long) {
context.dataStore.edit { preferences ->
preferences[PreferencesKeys.BEST_TIME] = newBestTime
}
}
}
private object PreferencesKeys {
val BEST_TIME = longPreferencesKey("BEST_TIME")
}
以及要添加到 build.gradle
的依赖项:
implementation "androidx.datastore:datastore-preferences:1.0.0"
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