ANDROID ROOM - COROUTINES & ROOM

VIEWMODEL & VIEWMODEL FACTORY

/* SleepTrackerViewModel.kt */
class SleepTrackerViewModel(
        val database: SleepDatabaseDao,
        application: Application) : AndroidViewModel(application) {
}

/* SleepTrackerViewModelFactory.kt */
class SleepTrackerViewModelFactory(
        private val dataSource: SleepDatabaseDao,
        private val application: Application) : ViewModelProvider.Factory {
    @Suppress("unchecked_cast")
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(SleepTrackerViewModel::class.java)) {
            return SleepTrackerViewModel(dataSource, application) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

DATA BINDING & FRAGMENT

<!-- fragment_sleep_tracker -->
    <data>
        <variable
            name="sleepTrackerViewModel"
            type="com.example.android.trackmysleepquality.sleeptracker.SleepTrackerViewModel" />
    </data>

/* SleepTrackerFragment.kt */
        val application = requireNotNull(this.activity).application
        val dataSource = SleepDatabase.getInstance(application).sleepDatabaseDao
        val sleepTrackerViewModelFactory = SleepTrackerViewModelFactory(dataSource, application)
        val sleepTrackerViewModel = ViewModelProvider(
                this, sleepTrackerViewModelFactory).get(SleepTrackerViewModel::class.java)
        binding.lifecycleOwner = viewLifecycleOwner
        binding.sleepTrackerViewModel = sleepTrackerViewModel

COROUTINES - CONCEPT

Concept
https://developer.android.com/courses/extras/multithreading
https://developer.android.com/codelabs/kotlin-android-training-coroutines-and-room#4

COROUTINES - COLLECT & DISPLAY THE DATA

class SleepTrackerViewModel(
        val database: SleepDatabaseDao,
        application: Application) : AndroidViewModel(application) {

    private var tonight = MutableLiveData<SleepNight?>()

    private val nights = database.getAllNights()

    val nightsString = Transformations.map(nights) {
        formatNights(it, application.resources)
    }

    init {
        initializeTonight()
    }

    private fun initializeTonight() {
        viewModelScope.launch {
            tonight.value = getTonightFromDatabase()
        }
    }

    fun onStartTracking() {
        viewModelScope.launch {
            val newNight = SleepNight()
            insert(newNight)
            tonight.value = getTonightFromDatabase()
        }
    }

    fun onStopTracking() {
        viewModelScope.launch {
            val oldNight = tonight.value ?: return@launch
            oldNight.endTimeMilli = System.currentTimeMillis()
            update(oldNight)
        }
    }

    fun onClear() {
        viewModelScope.launch {
            clear()
            tonight.value = null
        }
    }

    private suspend fun getTonightFromDatabase(): SleepNight? {
        var night = database.getTonight()
        if(night?.endTimeMilli != night?.startTimeMilli) {
            night = null
        }
        return night
    }

    private suspend fun insert(night: SleepNight) {
        database.insert(night)
    }

    private suspend fun update(night: SleepNight) {
        database.update(night)
    }

    private suspend fun clear() {
        database.clear()
    }
}

<!-- fragment_sleep_tracker.xml -->
         <TextView
                android:id="@+id/textview"
              		...
                android:text="@{sleepTrackerViewModel.nightsString}" />

        <Button
            android:id="@+id/start_button"
		       ...
            android:onClick="@{() -> sleepTrackerViewModel.onStartTracking()}" />
        <Button
            android:id="@+id/stop_button"
               ...
            android:onClick="@{() -> sleepTrackerViewModel.onStopTracking()}" />
        <Button
            android:id="@+id/clear_button"
               ...
            android:onClick="@{() -> sleepTrackerViewModel.onClear()}" />
        

SUMMARY

Learn more
https://developer.android.com/codelabs/kotlin-android-training-coroutines-and-room#8