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Flow block is not executing, call generated from ViewModel

Can't understand why the flow block doesn't execute and control returns back to ViewModel.
ViewModel code
fun getFilesFromServer() {
viewModelScope.launch(Dispatchers.IO) {
ftpRepository.getFilesFromServer()
.onEach { state ->
when (state) {
is Resource.Loading -> {
liveData.postValue(Resource.Loading())
}
}
}
}
Repository (Here the problem, control doesn't go inside flow {} block)
override suspend fun getFilesFromServer(): Flow<Resource<Response>> = flow {
emit(Resource.Loading())
ftpClient.connect(
Constants.SERVER_IP, Constants.PORT,
Constants.USER_NAME,
Constants.PASSWORD,
object : OnEZFtpCallBack<Void?> {
override fun onSuccess(response: Void?) {
requestFtpFileList()
}
override fun onFail(code: Int, msg: String) {
}
}
)
}
Thanks for your time...

Forgot to launch the flow
launchIn(this)
Complete code
fun getFilesFromServer() {
viewModelScope.launch(Dispatchers.IO) {
ftpRepository.getFilesFromServer()
.onEach { state ->
when (state) {
is Resource.Loading -> {
liveData.postValue(Resource.Loading())
}
}
}.launchIn(this)
}

How to implement loadstate with adapter, recyclerView?

I would like to implement a feature like loadStateFlow in Paging 3.
I do not use pagination in my implementation and it is not necessary in my case.
Could I make it another way?
I have found something like LoadingStateAdapter library
https://developer.android.com/reference/kotlin/androidx/paging/LoadStateAdapter
For now I get a list using method in the fragment:
private fun collectNotificationItems() {
vm.notificationData.collectWith(viewLifecycleOwner) {
notificationAdapter.items = it
}
}
This is implementation I would like to achieve, example is in paging3:
private fun collectItems() {
vm.items.collectWith(viewLifecycleOwner, adapter::submitData)
adapter.loadStateFlow.collectWith(viewLifecycleOwner) { loadState ->
vm.setLoadingState(loadState.refresh is LoadState.Loading)
val isEmpty =
loadState.source.refresh is LoadState.NotLoading && loadState.append.endOfPaginationReached && archiveAdapter.itemCount < 1
vm.setEmptyStateVisible(isEmpty)
}
}
Where methods are:
in ViewModel
fun setLoadingState(isLoading: Boolean) {
_areShimmersVisible.value = isLoading && !_isSwipingToRefresh.value
if (!isLoading) _isSwipingToRefresh.value = false
}
areShimmers and isSwiping are MutableStateFlow
Could you recommend any other options?
EDIT:
I have the whole implementation a little bit different.
I have use case to make it
class GetListItemDetailsUseCase #Inject constructor(private val dao: Dao): BaseFlowUseCase<Unit, List<ItemData>>() {
override fun create(params: Unit): Flow<List<ItemData>> {
return flow{
emit(dao.readAllData())
}
}
}
For now it looks like the code above.
How to use DateState in that case?
EDIT2:
class GetNotificationListItemDetailsUseCase #Inject constructor(private val notificationDao: NotificationDao): BaseFlowUseCase<Unit, DataState<List<NotificationItemsResponse.NotificationItemData>>>() {
override fun create(params: Unit): Flow<DataState<List<NotificationItemsResponse.NotificationItemData>>> {
return flow{
emit(DataState.Loading)
try {
emit(DataState.Success(notificationDao.readAllDataState()))
} catch(e: Exception) {
emit(DataState.Error(e)) // error, and send the exception
}
}
}
}
DAO
#Query("SELECT * FROM notification_list ORDER BY id ASC")
abstract suspend fun readAllDataState(): DataState<List<NotificationItemsResponse.NotificationItemData>>
/\ error beacause of it:
error: Not sure how to convert a Cursor to this method's return type
fragment
private suspend fun collectNotificationItems() {
vm.notificationData.collectLatest { dataState ->
when(dataState) {
is DataState.Error -> {
collectErrorState()
Log.d("collectNotificationItems", "Collect ErrorState")
}
DataState.Loading -> {
Log.d("collectNotificationItems", "Collect Loading")
}
is DataState.Success<*> -> {
vm.notificationData.collectWith(viewLifecycleOwner) {
notificationAdapter.items = it
notificationAdapter.notifyDataSetChanged()
Log.d("collectNotificationItems", "Collect Sucess")
}
}
}
}

You could use a utility class (usually called DataState or something like that).
sealed class DataState<out T> {
data class Success<out T>(val data: T) : DataState<T>()
data class Error(val exception: Exception) : DataState<Nothing>()
object Loading : DataState<Nothing>()
}
Then, you change your flow's return type from Flow<YourObject> to Flow<DataState<YourObject>> and emit the DataStates within a flow {} or channelFlow {} block.
val notificationsFlow: Flow<DataState<YourObject>> get() = flow {
emit(DataState.Loading) // when you collect, you will receive this DataState telling you that it's loading
try {
// networking/database stuff
emit(DataState.Success(yourResultObject))
} catch(e: Exception) {
emit(DataState.Error(e)) // error, and send the exception
}
}
Finally, just change your collect {} to be like:
notificationsFlow.collectLatest { dataState ->
when(dataState) {
is DataState.Error -> { } // error occurred, deal with it here
DataState.Loading -> { } // it's loading, show progress bar or something
is DataState.Success -> { } // data received from the flow, access it with dataState.data
}
}
For more information on this regard, check this out.

How to propagate the response of an async operation to the view using Jetpack Compose?

I have this sealed class:
sealed class Resource<out T> {
object Loading: Resource<Nothing>()
data class Success<out T>(val data: T): Resource<T>()
data class Failure(val message: String): Resource<Nothing>()
}
In the repository class I have this function that deletes an item from an API:
override suspend fun deleteItem(id: String) = flow {
try {
emit(Resource.Loading)
emit(Resource.Success(itemsRef.document(id).delete().await()))
} catch (e: Exception) {
emit(Resource.Failure(e.message))
}
}
The result of the delete operation is Void?. Now, in the ViewModel class I declare:
val state = mutableStateOf<Resource<Void?>>(Success(null))
And update it when the delete completes:
fun deleteItem(id: String) {
viewModelScope.launch {
repo.deleteItem(id).collect { response ->
state.value = response
}
}
}
I have created a Card and inside onClick I have added:
IconButton(
onClick = viewModel.deleteItem(id),
)
Which actually deletes that item form database correctly. But I cannot track the result of the operation. I tried using:
when(val res = viewModel.state.value) {
is Resource.Loading -> Log.d(TAG, "Loading")
is Resource.Success -> Log.d(TAG, "Success")
is Resource.Failure -> Log.d(TAG, "Failure")
}
But only the case Loading is triggered. No success/failure at all. What can be wrong here? As it really acts like a synchronous operation.

I've tested your approach without a repository, and compose part looks totally fine:
var i = 0
#Composable
fun TestScreen(viewModel: TestViewModel = viewModel()) {
val state by viewModel.state
Text(
when (val stateSmartCast = state) {
is Resource.Failure -> "Failure ${stateSmartCast.message}"
Resource.Loading -> "Loading"
is Resource.Success -> "Success ${stateSmartCast.data}"
}
)
Button(onClick = {
viewModel.deleteItem(++i)
}) {
}
}
class TestViewModel : ViewModel() {
val state = mutableStateOf<Resource<Int>>(Resource.Success(i))
fun deleteItem(id: Int) {
viewModelScope.launch {
deleteItemInternal(id).collect { response ->
state.value = response
}
}
}
suspend fun deleteItemInternal(id: Int) = flow {
try {
emit(Resource.Loading)
delay(1000)
if (id % 3 == 0) {
throw IllegalStateException("error on third")
}
emit(Resource.Success(id))
} catch (e: Exception) {
emit(Resource.Failure(e.message ?: e.toString()))
}
}
}
So the the problem looks like in this line itemsRef.document(id).delete().await()), or in your connection to the repository.

Try collecting in the composable function:
val state = viewModel.state.collectAsState()
Then you can do: when (val res = viewModel.state.value){...}.
However I am sceptical about the deleteItem in the repository returning a flow. Do you really need such thing? You can always map stuff in the viewModel.

Android: Firebase Object is null when using kotlin flow

My problem is, that when I try to get a document out of my database, that this document aka the object is always null. I only have this problem when I use Kotlin Coroutines to get the document out of my database. Using the standard approach with listeners do work.
EmailRepository
interface EmailRepository {
suspend fun getCalibratePrice(): Flow<EmailEntity?>
suspend fun getRepairPrice(): Flow<EmailEntity?>
}
EmailRepository Implementation
class EmailRepositoryImpl #Inject constructor(private val db: FirebaseFirestore) : EmailRepository {
fun hasInternet(): Boolean {
return true
}
// This works! When using flow to write a document, the document is written!
override fun sendEmail(email: Email)= flow {
emit(EmailStatus.loading())
if (hasInternet()) {
db.collection("emails").add(email).await()
emit(EmailStatus.success(Unit))
} else {
emit(EmailStatus.failed<Unit>("No Email connection"))
}
}.catch {
emit(EmailStatus.failed(it.message.toString()))
}.flowOn(Dispatchers.Main)
// This does not work! "EmailEntity" is always null. I checked the document path!
override suspend fun getCalibratePrice(): Flow<EmailEntity?> = flow {
val result = db.collection("emailprice").document("Kalibrieren").get().await()
emit(result.toObject<EmailEntity>())
}.catch {
}.flowOn(Dispatchers.Main)
// This does not work! "EmailEntity" is always null. I checked the document path!
override suspend fun getRepairPrice(): Flow<EmailEntity?> = flow {
val result = db.collection("emailprice").document("Reparieren").get().await()
emit(result.toObject<EmailEntity>())
}.catch {
}.flowOn(Dispatchers.Main)
}
Viewmodel where I get the data
init {
viewModelScope.launch {
withContext(Dispatchers.IO) {
if (subject.value != null){
when(subject.value) {
"Test" -> {
emailRepository.getCalibratePrice().collect {
emailEntity.value = it
}
}
"Toast" -> {
emailRepository.getRepairPrice().collect {
emailEntity.value = it
}
}
}
}
}
}
}
private val emailEntity = MutableLiveData<EmailEntity?>()
private val _subject = MutableLiveData<String>()
val subject: LiveData<String> get() = _subject
Fragment
#AndroidEntryPoint
class CalibrateRepairMessageFragment() : EmailFragment<FragmentCalibrateRepairMessageBinding>(
R.layout.fragment_calibrate_repair_message,
) {
// Get current toolbar Title and send it to the next fragment.
private val toolbarText: CharSequence by lazy { toolbar_title.text }
override val viewModel: EmailViewModel by navGraphViewModels(R.id.nav_send_email) { defaultViewModelProviderFactory }
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// Here I set the data from the MutableLiveData "subject". I don't know how to do it better
viewModel.setSubject(toolbarText.toString())
}
}
One would say, that the Firebase rules are the problems here, but that should not be the case here, because the database is open and using the listener approach does work.
I get the subject.value from my CalibrateRepairMessageFragment. When I don't check if(subject.value != null) I get a NullPointerException from my init block.
I will use the emailEntitiy only in my viewModel and not outside it.
I appreciate every help, thank you.
EDIT
This is the new way I get the data. The object is still null! I've also added Timber.d messages in my suspend functions which also never get executed therefore flow never throws an error.. With this new approach I don't get a NullPointerException anymore
private val emailEntity = liveData {
when(subject.value) {
"Test" -> emailRepository.getCalibratePrice().collect {
emit(it)
}
"Toast" -> emailRepository.getRepairPrice().collect {
emit(it)
}
// Else block is never executed, therefore "subject.value" is either Test or toast and the logic works. Still error when using flow!
else -> EmailEntity("ERROR", 0F)
}
}
I check if the emailEntity is null or not with Timber.d("EmailEntity is ${emailEntity.value}") in one of my functions.
I then set the price with val price = MutableLiveData(emailEntity.value?.basePrice ?: 1000F) but because emailentity is null the price is always 1000
EDIT 2
I have now further researched the problem and made a big step forward. When observing the emailEntity from a fragment like CalibrateRepairMessageFragment the value is no longer null.
Furthermore, when observing emailEntity the value is also not null in viewModel, but only when it is observed in one fragment! So how can I observe emailEntity from my viewModel or get the value from my repository and use it in my viewmodel?

Okay, I have solved my problem, this is the final solution:
Status class
sealed class Status<out T> {
data class Success<out T>(val data: T) : Status<T>()
class Loading<T> : Status<T>()
data class Failure<out T>(val message: String?) : Status<T>()
companion object {
fun <T> success(data: T) = Success<T>(data)
fun <T> loading() = Loading<T>()
fun <T> failed(message: String?) = Failure<T>(message)
}
}
EmailRepository
interface EmailRepository {
fun sendEmail(email: Email): Flow<Status<Unit>>
suspend fun getCalibratePrice(): Flow<Status<CalibrateRepairPricing?>>
suspend fun getRepairPrice(): Flow<Status<CalibrateRepairPricing?>>
}
EmailRepositoryImpl
class EmailRepositoryImpl (private val db: FirebaseFirestore) : EmailRepository {
fun hasInternet(): Boolean {
return true
}
override fun sendEmail(email: Email)= flow {
Timber.d("Executed Send Email Repository")
emit(Status.loading())
if (hasInternet()) {
db.collection("emails").add(email).await()
emit(Status.success(Unit))
} else {
emit(Status.failed<Unit>("No Internet connection"))
}
}.catch {
emit(Status.failed(it.message.toString()))
}.flowOn(Dispatchers.Main)
// Sends status and object to viewModel
override suspend fun getCalibratePrice(): Flow<Status<CalibrateRepairPricing?>> = flow {
emit(Status.loading())
val entity = db.collection("emailprice").document("Kalibrieren").get().await().toObject<CalibrateRepairPricing>()
emit(Status.success(entity))
}.catch {
Timber.d("Error on getCalibrate Price")
emit(Status.failed(it.message.toString()))
}
// Sends status and object to viewModel
override suspend fun getRepairPrice(): Flow<Status<CalibrateRepairPricing?>> = flow {
emit(Status.loading())
val entity = db.collection("emailprice").document("Kalibrieren").get().await().toObject<CalibrateRepairPricing>()
emit(Status.success(entity))
}.catch {
Timber.d("Error on getRepairPrice")
emit(Status.failed(it.message.toString()))
}
}
ViewModel
private lateinit var calibrateRepairPrice: CalibrateRepairPricing
private val _calirateRepairPriceErrorState = MutableLiveData<Status<Unit>>()
val calibrateRepairPriceErrorState: LiveData<Status<Unit>> get() = _calirateRepairPriceErrorState
init {
viewModelScope.launch {
when(_subject.value.toString()) {
"Toast" -> emailRepository.getCalibratePrice().collect {
when(it) {
is Status.Success -> {
calibrateRepairPrice = it.data!!
_calirateRepairPriceErrorState.postValue(Status.success(Unit))
}
is Status.Loading -> _calirateRepairPriceErrorState.postValue(Status.loading())
is Status.Failure -> _calirateRepairPriceErrorState.postValue(Status.failed(it.message))
}
}
else -> emailRepository.getRepairPrice().collect {
when(it) {
is Status.Success -> {
calibrateRepairPrice = it.data!!
_calirateRepairPriceErrorState.postValue(Status.success(Unit))
}
is Status.Loading -> _calirateRepairPriceErrorState.postValue(Status.loading())
is Status.Failure -> _calirateRepairPriceErrorState.postValue(Status.failed(it.message))
}
}
}
price.postValue(calibrateRepairPrice.head!!.basePrice)
}
}
You can now observe the status in one of your fragments (but you dont need to!)
Fragment
viewModel.calibrateRepairPriceErrorState.observe(viewLifecycleOwner) { status ->
when(status) {
is Status.Success -> requireContext().toast("Price successfully loaded")
is Status.Loading -> requireContext().toast("Price is loading")
is Status.Failure -> requireContext().toast("Error, Price could not be loaded")
}
}
This is my toast extensions function:
fun Context.toast(text: String, duration: Int = Toast.LENGTH_SHORT) {
Toast.makeText(this, text, duration).show()
}

How to achieve concurrency with Kotlin coroutines?

I have list of carousels and run over each carousel and based on the carousel query I do fetchAssets() and fetchAssets() is Kotlin suspended function but the problem is each function is called when the previous one is finished I want to achieve concurency?
uiScope.launch {
carousels.mapIndexed { index, carousel ->
when (val assetsResult = assetRepository.fetchAssets(carousel.query)) {
is Response.Success<List<Asset>> -> {
if (assetsResult.data.isNotEmpty()) {
val contentRow = ContentRow(assetsResult.data)
contentRows.add(contentRow)
contentRowsmutableData.postValue(contentRows)
}
}
is Response.Failure -> {
}
}
}
}
override suspend fun fetchAssets(query: String): Response<List<Asset>> {
return suspendCoroutine { cont ->doHttp(assetsEndpoint, JsonHttpCall("GET"),
object : JsonReaderResponseHandler() {
override fun onSuccess(jsonReader: JsonReader) {
val apiAsset = ApiAssetList(jsonReader)
cont.resume(Response.Success(apiAsset.items))
}
override fun onError(error: Error) {
cont.resume(Response.Failure("errorMessage"))
}
})
}
}```

You have to wrap your suspend function in an async block, then wait for all async operations to complete:
uiScope.launch {
val asyncList = carousels.map { carousel ->
async { assetRepository.fetchAssets(carousel.query) }
}
val results = asyncList.awaitAll()
results.forEach { result ->
when (result) {
is Response.Success -> TODO()
is Response.Failure -> TODO()
}
}
}
suspend fun fetchAssets(query: String): Response<List<Asset>>
Edit: if you want to update the UI as each completes, you need to change it like this:
carousels.forEach { carousel ->
uiScope.launch {
val result = fetchAssets(carousel.query)
when (result) {
is Response.Success -> {
if (result.data.isNotEmpty()) {
val contentRow = ContentRow(result.data)
contentRows.add(contentRow)
contentRowsmutableData.postValue(contentRows)
}
}
is Response.Failure -> TODO()
}
}
}
Check this for concurrency with Coroutines.