MainScreenViewModel.kt

class MainScreenViewModel (
    application: Application
) : ViewModel() {

    private val preferencesManager = PreferencesManager(application)
    val imageCategoryIndex = preferencesManager.imageCategoryPref
    private var workManager = WorkManager.getInstance(application)

    init {
        imageCategoryIndex.onEach {
            setWork(it)
        }.launchIn(viewModelScope)
    }

    fun setCategory(categoryIndex: Int) {
        viewModelScope.launch {
            preferencesManager.setImageCategory(categoryIndex)
        }
    }

    private fun setWork(categoryIndex: Int) {
        val inputData = Data.Builder().putInt(CURRENT_CATEGORY, categoryIndex).build()
        val constraints = Constraints.Builder()
            .setRequiredNetworkType(NetworkType.CONNECTED)
            .build()
        val work = PeriodicWorkRequestBuilder<RemoteImageWorker>(15, TimeUnit.MINUTES)
            .setConstraints(constraints)
            .setInputData(inputData)
            .build()
        workManager.enqueue(work)
    }

}

class MainScreenViewModelFactory(private val application: Application) : ViewModelProvider.Factory {

    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return if (modelClass.isAssignableFrom(MainScreenViewModel::class.java)) {
            MainScreenViewModel(application) as T
        } else {
            throw IllegalArgumentException("Unknown ViewModel class")
        }
    }
}