Custom Lazy<Deferred<T>> fun leads to frame skipping and crash - android-studio

Question

I'm following the MVVM using ROOM,Retrofit,Koin DI etc. and inside of my MainFragment class i'm calling my bindUI() function that is responsible for fetching data through the viewModel asynchronously using kotlin coroutines as you can see below. Now, when i run my app it crashes almost immediately.
Here's what i tried: I placed a breakpoint inside of bindUI() and specifically on my first .await() call on val currentWeather and run the debugger. I noticed that as soon as the await call is resolved and the result is returned to the variable, the application crashes saying that Skipped 1501 frames! The application may be doing too much work on its main thread. and then Skipped 359 frames! The application may be doing too much work on its main thread.
Now, why would that be since i'm running those async calls inside of the Dispathcers.IO thread and at the moment of the crash i'm only executing one await() call?
Here's my MainFragment class:
const val UNIT_SYSTEM_KEY = "UNIT_SYSTEM"
class MainFragment(
private val weatherUnitConverter: WeatherUnitConverter
) : ScopedFragment() {
// Lazy inject the view model
private val viewModel: WeatherViewModel by viewModel()
private lateinit var unitSystem:String
private val TAG = MainFragment::class.java.simpleName
// View declarations
private lateinit var lcHourlyForecasts: LineChart
private lateinit var weeklyForecastRCV: RecyclerView
private lateinit var scrollView: NestedScrollView
private lateinit var detailsExpandedArrow:ImageView
private lateinit var detailsExpandedLayout: LinearLayout
private lateinit var dailyWeatherDetailsHeader:LinearLayout
private lateinit var settingsBtnImageView:ImageView
private lateinit var unitSystemImgView:ImageView
private lateinit var locationTxtView:TextView
// Current weather view declarations
private lateinit var currentWeatherDate:TextView
private lateinit var currentWeatherTemp:TextView
private lateinit var currentWeatherSummaryText:TextView
private lateinit var currentWeatherSummaryIcon:ImageView
private lateinit var currentWeatherPrecipProb:TextView
// Today/Details weather view declarations
private lateinit var todayHighLowTemp:TextView
private lateinit var todayWindSpeed:TextView
private lateinit var todayFeelsLike:TextView
private lateinit var todayUvIndex:TextView
private lateinit var todayPrecipProb:TextView
private lateinit var todayCloudCover:TextView
private lateinit var todayHumidity:TextView
private lateinit var todayPressure:TextView
private lateinit var todaySunriseTime:TextView
private lateinit var todaySunsetTime:TextView
// OnClickListener to handle the current weather's "Details" layout expansion/collapse
private val onCurrentWeatherDetailsClicked:View.OnClickListener = View.OnClickListener {
if(detailsExpandedLayout.visibility == View.GONE) {
detailsExpandedLayout.visibility = View.VISIBLE
detailsExpandedArrow.setImageResource(R.drawable.ic_arrow_up_black)
}
else {
detailsExpandedLayout.visibility = View.GONE
detailsExpandedArrow.setImageResource(R.drawable.ic_down_arrow)
}
}
// OnClickListener to allow navigating from this fragment to the settings one
private val onSettingsButtonClicked:View.OnClickListener = View.OnClickListener {
(activity as MainActivity).openSettingsPage()
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View {
val view = inflater.inflate(R.layout.main_fragment, container, false)
// View initializations
scrollView = view.findViewById(R.id.nsv_main)
lcHourlyForecasts = view.findViewById(R.id.lc_hourly_forecasts)
detailsExpandedLayout = view.findViewById(R.id.ll_expandable)
detailsExpandedArrow = view.findViewById(R.id.iv_arrow)
dailyWeatherDetailsHeader = view.findViewById(R.id.current_weather_details_header)
dailyWeatherDetailsHeader.setOnClickListener(onCurrentWeatherDetailsClicked)
settingsBtnImageView = view.findViewById(R.id.settings)
settingsBtnImageView.setOnClickListener(onSettingsButtonClicked)
unitSystemImgView = view.findViewById(R.id.unitSystemImg)
locationTxtView = view.findViewById(R.id.location)
initCurrentWeatherViews(view)
initTodayWeatherViews(view)
// RCV initialization
weeklyForecastRCV = view.findViewById(R.id.weekly_forecast_rcv)
weeklyForecastRCV.adapter = WeeklyWeatherAdapter(listOf(),viewModel.preferences, this,weatherUnitConverter) // init the adapter with empty data
weeklyForecastRCV.setHasFixedSize(true)
// Disable nested scrolling to control the RCV scrolling via the parent NestedScrollView
weeklyForecastRCV.isNestedScrollingEnabled = false
return view
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
initLineChart()
bindUI()
}
private fun SharedPreferences.stringLiveData(key: String, defValue: String): SharedPreferenceLiveData<String> {
return SharedPreferenceStringLiveData(this, key, defValue)
}
private fun bindUI() = launch(Dispatchers.Main) {
//TODO:sp get the coordinates dynamically
viewModel.setLocCoordinates(37.8267,-122.4233)
// fetch current weather
val currentWeather = viewModel.currentWeatherData.await()
// fetch weekly weather
val weeklyWeather = viewModel.weeklyWeatherEntries.await()
// fetch the location
val weatherLocation = viewModel.weatherLocation.await()
// Observe the location for changes
weatherLocation.observe(viewLifecycleOwner, Observer { location ->
if(location == null) return#Observer
launch {
updateLocation(location)
}
})
// Observe the current weather live data
currentWeather.observe(viewLifecycleOwner, Observer {currently ->
if(currently == null) return#Observer
setCurrentWeatherDate(currently.time.toDouble())
// Observe the unit system sharedPrefs live data for changes
viewModel.preferences.stringLiveData(UNIT_SYSTEM_KEY, UnitSystem.SI.name.toLowerCase(Locale.ROOT))
.observe(viewLifecycleOwner, Observer {unitSystem ->
when(unitSystem) {
UnitSystem.SI.name.toLowerCase(Locale.ROOT) -> {
setCurrentWeatherTemp(currently.temperature)
setUnitSystemImgView(unitSystem)
}
UnitSystem.US.name.toLowerCase(Locale.ROOT) -> {
setCurrentWeatherTemp(weatherUnitConverter.convertToFahrenheit(
currently.temperature
))
setUnitSystemImgView(unitSystem)
}
}
})
setCurrentWeatherSummaryText(currently.summary)
setCurrentWeatherSummaryIcon(currently.icon)
setCurrentWeatherPrecipProb(currently.precipProbability)
})
// observe the weekly weather live data
weeklyWeather.observe(viewLifecycleOwner, Observer {weatherEntries ->
if(weatherEntries == null) return#Observer
// update the recyclerView with the new data
(weeklyForecastRCV.adapter as WeeklyWeatherAdapter).updateWeeklyWeatherData(weatherEntries)
initTodayData(weatherEntries[0])
})
}
/**
* Uses the location param's lat & longt values
* to determine the selected location and updates
* the view.
*/
private suspend fun updateLocation(location: WeatherLocation) {
withContext(Dispatchers.IO) {
val geocoder = Geocoder(activity,Locale.getDefault())
try {
val addr = geocoder.getFromLocation(location.latitude,location.longitude,1)
val adobj = addr[0]
locationTxtView.text = adobj.countryName
} catch (e:IOException) {
Log.d(TAG, e.printStackTrace().toString())
}
}
}
/**
* Initializes the views for the current weather.
*/
private fun initCurrentWeatherViews(view: View) {
currentWeatherDate = view.findViewById(R.id.current_weather_date)
currentWeatherTemp = view.findViewById(R.id.current_temp_main)
currentWeatherSummaryText = view.findViewById(R.id.current_weather_summary_text)
currentWeatherSummaryIcon = view.findViewById(R.id.current_weather_summary_icon)
currentWeatherPrecipProb = view.findViewById(R.id.current_weather_precip_text)
}
/**
* Initializes the views for the Detailed Today weather view.
*/
private fun initTodayWeatherViews(view: View?) {
if(view == null) return
todayHighLowTemp = view.findViewById(R.id.today_lowHighTemp)
todayWindSpeed = view.findViewById(R.id.today_windSpeed)
todayFeelsLike = view.findViewById(R.id.today_feelsLike)
todayUvIndex = view.findViewById(R.id.today_uvIndex)
todayPrecipProb = view.findViewById(R.id.today_precipProb)
todayCloudCover = view.findViewById(R.id.today_cloudCover)
todayHumidity = view.findViewById(R.id.today_humidity)
todayPressure = view.findViewById(R.id.today_pressure)
todaySunriseTime = view.findViewById(R.id.today_sunriseTime)
todaySunsetTime = view.findViewById(R.id.today_sunsetTime)
}
private fun setUnitSystemImgView(unitSystem:String) {
val resource = when(unitSystem) {
UnitSystem.SI.name.toLowerCase(Locale.ROOT)
-> R.drawable.ic_celsius
UnitSystem.US.name.toLowerCase(Locale.ROOT)
-> R.drawable.ic_fahrenheit
else -> R.drawable.ic_celsius
}
unitSystemImgView.setImageResource(resource)
}
/**
* Links the data to the view for the Today(Details) Weather View.
*/
private fun initTodayData(weekDayWeatherEntry: WeekDayWeatherEntry) {
// Observe the unit system sharedPrefs live data for changes
viewModel.preferences.stringLiveData(UNIT_SYSTEM_KEY, UnitSystem.SI.name.toLowerCase(Locale.ROOT))
.observe(viewLifecycleOwner, Observer {unitSystem ->
when(unitSystem) {
UnitSystem.SI.name.toLowerCase(Locale.ROOT) -> {
setTodayWeatherLowHighTemp(weekDayWeatherEntry.temperatureLow,weekDayWeatherEntry.temperatureHigh)
setTodayWeatherWindSpeed(weekDayWeatherEntry.windSpeed,unitSystem)
setTodayWeatherFeelsLike(weekDayWeatherEntry.apparentTemperatureLow,weekDayWeatherEntry.apparentTemperatureHigh)
}
UnitSystem.US.name.toLowerCase(Locale.ROOT) -> {
setTodayWeatherLowHighTemp(weatherUnitConverter.convertToFahrenheit(
weekDayWeatherEntry.temperatureLow),
weatherUnitConverter.convertToFahrenheit(
weekDayWeatherEntry.temperatureHigh))
setTodayWeatherWindSpeed(weatherUnitConverter.convertToMiles(weekDayWeatherEntry.windSpeed),unitSystem)
setTodayWeatherFeelsLike(weatherUnitConverter.convertToFahrenheit(
weekDayWeatherEntry.apparentTemperatureLow)
,weatherUnitConverter.convertToFahrenheit(weekDayWeatherEntry.apparentTemperatureHigh))
}
}
})
setTodayWeatherUvIndex(weekDayWeatherEntry.uvIndex)
setTodayWeatherPrecipProb(weekDayWeatherEntry.precipProbability)
setTodayWeatherCloudCover(weekDayWeatherEntry.cloudCover)
setTodayWeatherHumidity(weekDayWeatherEntry.humidity)
setTodayWeatherPressure(weekDayWeatherEntry.pressure)
setTodayWeatherSunriseTime(weekDayWeatherEntry.sunriseTime)
setTodayWeatherSunsetTime(weekDayWeatherEntry.sunsetTime)
}
...
}
WeatherViewModel.kt:
class WeatherViewModel(
private val forecastRepository: ForecastRepository,
context:Context
) : ViewModel() {
private var mLatitude:Double = 0.0
private var mLongitute:Double = 0.0
private val appContext = context.applicationContext
// Retrieve the sharedPrefs
val preferences:SharedPreferences
get() = PreferenceManager.getDefaultSharedPreferences(appContext)
// This will run only when currentWeatherData is called from the View
val currentWeatherData by lazyDeferred {
forecastRepository.getCurrentWeather(mLatitude, mLongitute)
}
val weeklyWeatherEntries by lazyDeferred {
val currentDateEpoch = LocalDate.now().toEpochDay()
forecastRepository.getWeekDayWeatherList(mLatitude, mLongitute, currentDateEpoch)
}
val weatherLocation by lazyDeferred {
forecastRepository.getWeatherLocation()
}
fun setLocCoordinates(latitude:Double,longitude:Double) {
mLatitude = latitude
mLongitute = longitude
}
}
Here's my custom Lazy<Deferred<T>> fun inside of my Delegates.kt file:
fun<T> lazyDeferred(block: suspend CoroutineScope.() -> T) : Lazy<Deferred<T>> {
return lazy {
GlobalScope.async(start = CoroutineStart.LAZY) {
block.invoke(this)
}
}
}
Here's my repository class just in case:
private const val WEEKLY_FORECAST_DAYS_COUNT = 7
/**
* The Repository class responsible
* for caching the downloaded weather data
* and for swapping between different data sources.
*/
class ForecastRepositoryImpl(
private val currentWeatherDao: CurrentWeatherDao,
private val weekDayWeatherDao: WeekDayWeatherDao,
private val weatherLocationDao: WeatherLocationDao,
private val locationProvider: LocationProvider,
private val weatherNetworkDataSource: WeatherNetworkDataSource
) : ForecastRepository {
init {
weatherNetworkDataSource.apply {
// Persist downloaded data
downloadedCurrentWeatherData.observeForever { newCurrentWeather: CurrentWeatherResponse? ->
persistFetchedCurrentWeather(newCurrentWeather!!)
}
downloadedWeeklyWeatherData.observeForever { newWeeklyWeather: WeeklyWeatherResponse? ->
persistFetchedWeeklyWeather(newWeeklyWeather!!)
}
}
}
override suspend fun getCurrentWeather(latitude:Double,longitude:Double): LiveData<CurrentWeatherEntry> {
return withContext(Dispatchers.IO) {
initWeatherData(latitude,longitude)
return#withContext currentWeatherDao.getCurrentWeather()
}
}
override suspend fun getWeekDayWeatherList(latitude: Double,longitude: Double,time:Long): LiveData<out List<WeekDayWeatherEntry>> {
return withContext(Dispatchers.IO) {
initWeatherData(latitude,longitude)
return#withContext weekDayWeatherDao.getFutureWeather(time)
}
}
override suspend fun getWeatherLocation(): LiveData<WeatherLocation> {
return withContext(Dispatchers.IO) {
return#withContext weatherLocationDao.getWeatherLocation()
}
}
private suspend fun initWeatherData(latitude:Double,longitude:Double) {
// retrieve the last weather location from room
val lastWeatherLocation = weatherLocationDao.getWeatherLocation().value
if(lastWeatherLocation == null ||
locationProvider.hasLocationChanged(lastWeatherLocation)) { // then this is the first time we are launching the app
fetchCurrentWeather()
fetchWeeklyWeather()
return
}
if(isFetchCurrentNeeded(lastWeatherLocation.zonedDateTime))
fetchCurrentWeather()
if(isFetchWeeklyNeeded())
fetchWeeklyWeather()
}
/**
* Checks if the current weather data should be re-fetched.
* #param lastFetchedTime The time at which the current weather data were last fetched
* #return True or false respectively
*/
private fun isFetchCurrentNeeded(lastFetchedTime: ZonedDateTime) : Boolean {
val thirtyMinutesAgo = ZonedDateTime.now().minusMinutes(30)
return lastFetchedTime.isBefore(thirtyMinutesAgo)
}
/**
* Fetches the Current Weather data from the WeatherNetworkDataSource.
*/
private suspend fun fetchCurrentWeather() {
weatherNetworkDataSource.fetchCurrentWeather(
locationProvider.getPreferredLocationLat(),
locationProvider.getPreferredLocationLong()
)
}
private fun isFetchWeeklyNeeded(): Boolean {
val todayEpochTime = LocalDate.now().toEpochDay()
val futureWeekDayCount = weekDayWeatherDao.countFutureWeekDays(todayEpochTime)
return futureWeekDayCount < WEEKLY_FORECAST_DAYS_COUNT
}
private suspend fun fetchWeeklyWeather() {
weatherNetworkDataSource.fetchWeeklyWeather(
locationProvider.getPreferredLocationLat(),
locationProvider.getPreferredLocationLong()
)
}
/**
* Caches the downloaded current weather data to the local
* database.
* #param fetchedCurrentWeather The most recently fetched current weather data
*/
private fun persistFetchedCurrentWeather(fetchedCurrentWeather:CurrentWeatherResponse) {
// Using a GlobalScope since a Repository class doesn't have a lifecycle
GlobalScope.launch(Dispatchers.IO) {
// cache the data
currentWeatherDao.upsert(fetchedCurrentWeather.currentWeatherEntry)
weatherLocationDao.upsert(fetchedCurrentWeather.location)
}
}
/**
* Caches the downloaded weekly weather data to the local
* database.
* #param fetchedWeeklyWeather The most recently fetched weekly weather data
*/
private fun persistFetchedWeeklyWeather(fetchedWeeklyWeather: WeeklyWeatherResponse) {
fun deleteOldData() {
val time = LocalDate.now().toEpochDay()
weekDayWeatherDao.deleteOldEntries(time)
}
GlobalScope.launch(Dispatchers.IO) {
deleteOldData()
val weekDayEntriesList = fetchedWeeklyWeather.weeklyWeatherContainer.weekDayEntries
weekDayWeatherDao.insert(weekDayEntriesList)
}
}
}
EDIT: Here's the crash log i found out about earlier today:
2020-04-13 01:43:48.628 26875-26904/com.nesoinode.flogaweather E/AndroidRuntime: FATAL EXCEPTION: DefaultDispatcher-worker-2
Process: com.nesoinode.flogaweather, PID: 26875
java.lang.NullPointerException: Attempt to invoke virtual method 'int com.nesoinode.flogaweather.model.db.entity.WeatherLocation.getId()' on a null object reference
at com.nesoinode.flogaweather.model.db.dao.WeatherLocationDao_Impl$1.bind(WeatherLocationDao_Impl.java:34)
at com.nesoinode.flogaweather.model.db.dao.WeatherLocationDao_Impl$1.bind(WeatherLocationDao_Impl.java:26)
at androidx.room.EntityInsertionAdapter.insert(EntityInsertionAdapter.java:63)
at com.nesoinode.flogaweather.model.db.dao.WeatherLocationDao_Impl.upsert(WeatherLocationDao_Impl.java:52)
at com.nesoinode.flogaweather.model.repository.ForecastRepositoryImpl$persistFetchedCurrentWeather$1.invokeSuspend(ForecastRepositoryImpl.kt:131)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:561)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:727)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:667)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:655)
It's pointing to this part of my repository class as the root cause. I can't tell why though.
private fun persistFetchedCurrentWeather(fetchedCurrentWeather:CurrentWeatherResponse) {
// Using a GlobalScope since a Repository class doesn't have a lifecycle
GlobalScope.launch(Dispatchers.IO) {
// cache the data
currentWeatherDao.upsert(fetchedCurrentWeather.currentWeatherEntry)
weatherLocationDao.upsert(fetchedCurrentWeather.location)
}
}
UPDATE #2:
CurrentWeatherEntry :
const val CURRENT_WEATHER_ID = 0
#Entity(tableName = "current_weather")
data class CurrentWeatherEntry(
val time: Long, // epoch timestamp
val icon: String,
val summary: String,
val precipProbability: Double,
val temperature: Double
) {
#PrimaryKey(autoGenerate = false)
var id:Int = CURRENT_WEATHER_ID
}
WeatherLocation:
const val WEATHER_LOCATION_ID = 0
#Entity(tableName = "weather_location")
data class WeatherLocation(
val latitude: Double,
val longitude: Double,
val timezone: String
) {
#PrimaryKey(autoGenerate = false)
var id:Int = WEATHER_LOCATION_ID
private var epochTimeVal:Long = 0
val zonedDateTime:ZonedDateTime
get() {
val instant = Instant.ofEpochMilli(this.epochTimeVal)
val zoneId = ZoneId.of(timezone)
return ZonedDateTime.ofInstant(instant,zoneId)
}
fun setEpochTimeVal(time:Long) {
this.epochTimeVal = time}
fun getEpochTimeVal() : Long = epochTimeVal
}
and CurrentWeatherResponse:
data class CurrentWeatherResponse(
// Tells GSON that the "currently" field of the JSON returned by the
// API should be tied with our CurrentWeatherEntry data class
#SerializedName("currently")
val currentWeatherEntry: CurrentWeatherEntry,
#Embedded
val location: WeatherLocation
) {
init {
location.setEpochTimeVal(currentWeatherEntry.time)
}
}

Answer 1

According to the further diagnosis you made, the problem is unrelated to lazyDeferred, blocking the main thread, or coroutines in general. Your CurrentWeatherDao sometimes returns a CurrentWeatherResponse with location == null.

Answer 2

You never specified where forecastRepository.getWeatherLocation() should be executed so it gets executed on the dispatcher of your bindUI function which is Dispatchers.Main.
This means the request blocks your UI thread and causes the warning you're seeing in the log.
You need to specify that it executes on a separate dispatcher so the UI can continue updating normally:
lazyDeferred {
withContext(Dispatchers.IO) {
forecastRepository.getWeatherLocation()
}
}
As a separate issue, your lazyDeferred is slightly redundant in that it is "double"-lazy. You could remove the outer Lazy<T> and it would still work exactly the same way, or remove the start = CoroutineStart.LAZY and have the result arrive slightly sooner. (This essentially depends on whether the request starts when the Lazy is resolved, or when Deferred.await is called)