Develop Reference

StateFlow collect not firing for list type

#HiltViewModel
class HistoryViewModel #Inject constructor(private val firebaseRepository: FirebaseRepository) :
ViewModel() {
private val translateList: MutableList<Translate> = mutableListOf()
private val _translateListState: MutableStateFlow<List<Translate>> =
MutableStateFlow(translateList)
val translateListState = _translateListState.asStateFlow()
init {
listenToSnapshotData()
}
private suspend fun addItemToList(translate: Translate) {
Log.d("customTag", "item added adapter $translate")
translateList.add(translate)
_translateListState.emit(translateList)
}
private suspend fun removeItemFromList(translate: Translate) {
Log.d("customTag", "item removed adapter $translate")
val indexOfItem = translateList.indexOfFirst {
it.id == translate.id
}
if (indexOfItem != -1) {
translateList.removeAt(indexOfItem)
_translateListState.emit(translateList)
}
}
private suspend fun updateItemFromList(translate: Translate) {
Log.d("customTag", "item modified adapter $translate")
val indexOfItem = translateList.indexOfFirst {
it.id == translate.id
}
if (indexOfItem != -1) {
translateList[indexOfItem] = translate
_translateListState.emit(translateList)
}
}
private fun listenToSnapshotData() {
viewModelScope.launch {
firebaseRepository.translateListSnapshotListener().collect { querySnapshot ->
querySnapshot?.let {
for (document in it.documentChanges) {
val translateData = document.document.toObject(Translate::class.java)
when (document.type) {
DocumentChange.Type.ADDED -> {
addItemToList(translate = translateData)
}
DocumentChange.Type.MODIFIED
-> {
updateItemFromList(translate = translateData)
}
DocumentChange.Type.REMOVED
-> {
removeItemFromList(translate = translateData)
}
}
}
}
}
}
}
}
Here data comes properly in querySnapshot in listenToSnapshotData function. And post that it properly calls corresponding function to update the list.
But after this line _translateListState.emit(translateList) flow doesn't go to corresponding collectLatest
private fun observeSnapShotResponse() {
lifecycleScope.launch {
repeatOnLifecycle(Lifecycle.State.STARTED) {
historyViewModel.translateListState.collectLatest {
Log.d("customTag", "calling submitList from fragment")
translateListAdapter.submitList(it)
}
}
}
}
calling submitList from fragment is called once at the start, but as & when data is modified in list viewmodel, callback doesn't come to collectLatest

This is from StateFlow documentation:
Values in state flow are conflated using Any.equals comparison in a similar way to distinctUntilChanged operator. It is used to conflate incoming updates to value in MutableStateFlow and to suppress emission of the values to collectors when new value is equal to the previously emitted one.
You are trying to emit the same instance of List all the time, which has no effect because of what is written in the docs. You will have to create new instance of the list every time.

calling an api multiple times using WorkManager in android

I want to call an api multiple times using WorkManager.
where idsArrayList is a list of ids.
I send each id in the api as Path to get response and similarly for other ids.
I want the workManager to return success after it has called api for all ids.
But the problem is WorkManager only returns SUCCESS for one id from the list. This is the first time I'm using WorkManager and I tried starting work manager for every id too by iterating over idsList one by one and making instance of workManger for every id in the for loop. But I thought sending the idsList as data in the workmanager and then itering over ids from inside doWork() would be better, but it's not working like I want and I don't understand why. Here's my code:
class MyWorkManager(appContext: Context, workerParams: WorkerParameters):
Worker(appContext, workerParams) {
private lateinit var callGrabShifts: Call<ConfirmStatus>
override fun doWork(): Result {
val idsList = inputData.getStringArray("IDS_LIST")
val idsArrayList = idsList?.toCollection(ArrayList())
var response = ""
if (idsArrayList != null) {
try {
response = callConfirmShiftApi(idsArrayList)
if (response.contains("CONFIRM")) {
return Result.success()
}
} catch (e: Exception) {
e.printStackTrace()
return Result.failure()
}
}
return Result.retry()
}
private fun callConfirmShiftApi(idsArrayList: ArrayList<String>): String {
var response = ""
for ((index, id) in idsArrayList.withIndex()) {
response = callApiForId(id)
if(index == idsArrayList.lastIndex) {
response = "CONFIRM"
}
}
return response
}
private fun callApiForId(id: String): String {
var shiftGrabStatus = ""
callGrabShifts = BaseApp.apiInterface.confirmGrabAllShifts(BaseApp.userId, id)
callGrabShifts.enqueue(object : Callback<ConfirmStatus> {
override fun onResponse(call: Call<ConfirmStatus>, response: Response<ConfirmStatus>) {
if (response.body() != null) {
shiftGrabStatus = response.body()!!.status
if (shiftGrabStatus != null) {
if (shiftGrabStatus.contains("CONFIRM")) {
val shiftNumber = ++BaseApp.noOfShiftsGrabbed
sendNotification(applicationContext)
shiftGrabStatus = "CONFIRM"
return
} else {
shiftGrabStatus = "NOT CONFIRM"
return
}
} else {
shiftGrabStatus = "NULL"
return
}
} else {
shiftGrabStatus = "NULL"
return
}
}
override fun onFailure(call: Call<ConfirmStatus>, t: Throwable) {
shiftGrabStatus = "FAILURE"
return
}
})
return shiftGrabStatus
}
}
And this is the code where I'm starting the WorkManager:
private fun confirmShiftApi(availableShiftsIdList: ArrayList<String>) {
val data = Data.Builder()
data.putStringArray("IDS_LIST", availableShiftsIdList.toArray(arrayOfNulls<String>(availableShiftsIdList.size)))
val oneTimeWorkRequest = OneTimeWorkRequestBuilder<MyWorkManager>().setInputData(data.build())
.build()
WorkManager.getInstance(applicationContext).enqueue(oneTimeWorkRequest)
WorkManager.getInstance(this).getWorkInfoByIdLiveData(oneTimeWorkRequest.id)
.observe(this, Observer { workInfo: WorkInfo? ->
if (workInfo != null && workInfo.state.isFinished) {
val progress = workInfo.progress
}
Log.d("TESTING", "(MainActivity) : observing work manager - workInfo?.state - ${workInfo?.state}")
})
}
Any suggestions what I might be doing wrong or any other alternative to perform the same? I chose workmanager basicaly to perform this task even when app is closed and for learning purposes as I haven't used WorkManager before. But would switch to other options if this doesn't work.

I tried the following things:
removed the 'var response line in every method that I'm using to set the response, though I added it temporarily just for debugging earlier but it was causing an issue.
I removed the check for "CONFIRM" in doWork() method and just made the api calls, removed the extra return lines.
I tried adding manual delay in between api calls for each id.
I removed the code where I'm sending the ids data from my activity before calling workmanager and made the api call to fetch those ids inside workmanager and added more delay in between those calls to that keep running in background to check for data one round completes(to call api for all ids that were fetched earlier, it had to call api again to check for more ids on repeat)
I removed the extra api calls from onRestart() and from other conditons that were required to call api again.
I tested only one round of api calls for all ids with delay and removed the repeated call part just to test first. Didn't work.
None of the above worked, it just removed extra lines of code.
This is my final code that is tested and It cleared my doubt. Though it didn't fix this issue as the problem was because of backend server and Apis were returning failure in onResponse callback for most ids(when calls are made repeatedly using a for loop for each id) except first id and randomly last id from the list sometimes(with delay) for the rest of the ids it didn't return CONFIRM status message from api using Workmanager. Adding delay didn't make much difference.
Here's my Workmanager code:
class MyWorkManager(appContext: Context, workerParams: WorkerParameters):
Worker(appContext, workerParams) {
private lateinit var callGrabShifts: Call<ConfirmStatus>
override fun doWork(): Result {
val idsList = inputData.getStringArray("IDS_LIST")
val idsArrayList = idsList?.toCollection(ArrayList())
if (idsArrayList != null) {
try {
response = callConfirmShiftApi(idsArrayList)
if (response.contains("CONFIRM")) {
return Result.success()
}
} catch (e: Exception) {
e.printStackTrace()
return Result.failure()
}
}
return Result.success()
}
private fun callConfirmShiftApi(idsArrayList: ArrayList<String>): String {
for ((index, id) in idsArrayList.withIndex()) {
response = callApiForId(id)
Thread.sleep(800)
if(index == idsArrayList.lastIndex) {
response = "CONFIRM"
}
}
return response
}
private fun callApiForId(id: String): String {
callGrabShifts = BaseApp.apiInterface.confirmGrabAllShifts(BaseApp.userId, id)
callGrabShifts.enqueue(object : Callback<ConfirmStatus> {
override fun onResponse(call: Call<ConfirmStatus>, response: Response<ConfirmStatus>) {
if (response.body() != null) {
shiftGrabStatus = response.body()!!.status
if (shiftGrabStatus != null) {
if (shiftGrabStatus.contains("CONFIRM")) {
return
} else {
return
}
} else {
return
}
} else {
return
}
}
override fun onFailure(call: Call<ConfirmStatus>, t: Throwable) {
return
}
})
return shiftGrabStatus
}
Eventually this problem(when an individual call is made for an id, it always returns success but when i call the api for every id using a loop, it only returns success for first call and failure for others) was solved using Service, it didn't have a complete success rate from apis either, but for 6/11 ids the api returned success(400ms delay between each api call), so it served the purpose for now.

How to Wait response from Server in forEach with Coroutines

I recently started working with coroutines.
The task is that I need to check the priority parameter from the List and make a request to the server, if the response from the server is OK, then stop the loop.
var minPriority = 0
list.forEach { model ->
if (model.priority > minPriority) {
makeRequest(model.value)
minPriority = model.priority
}
}
private fun makeRequest(value: String) {
scope.launch() {
val response = restApi.makeRequest()
if response.equals("OK") {
**stop list foreach()**
}
}
}
In RxJava, this was done using the retryWhen() operator, tell me how to implement this in Coroutines?

I suggest making your whole code suspendable, not only the body of makeRequest() function. This way you can run the whole operation in the background, but internally it will be sequential which is easier to code and maintain.
It could be something like this:
scope.launch() {
var minPriority = 0
list.forEach { model ->
if (model.priority > minPriority) {
val response = restApi.makeRequest()
if response.equals("OK") {
return#forEach
}
minPriority = model.priority
}
}
}
Of if you need to keep your makeRequest() function separate:
fun myFunction() {
scope.launch() {
var minPriority = 0
list.forEach { model ->
if (model.priority > minPriority) {
if (makeRequest(model.value)) {
return#forEach
}
minPriority = model.priority
}
}
}
}
private suspend fun makeRequest(value: String): Boolean {
val response = restApi.makeRequest()
return response.equals("OK")
}

Kotlin Coroutine Retrofit - Chain network calls

I'm trying to use Kotlin Coroutines + Retrofit to make my network calls, but my current implementation has two problems.
A) It only returns once my loop has completed.
B) it seems to wait for each call in my loop to complete before making the next one.
The API I'm interacting with requires me to make an initial fetch, returning an array of itemId's
[ 1234, 3456, 3456 ... ]
and for each item in the above response, fetch that item with id
{ id: 1234, "name": "banana" ... }
My current implementation is as follows, what am I doing wrong?
suspend operator fun invoke(feedType: String): NetworkResult<List<MyItem>> = withContext(Dispatchers.IO) {
val itemList: MutableList< MyItem > = mutableListOf()
val result = repository.fetchItems()
when (result) {
is NetworkResult.Success -> {
itemList.addAll(result.data)
for (i in itemList) {
val emptyItem = result.data[i]
val response = repository.fetchItem(emptyItem.id)
when (response) {
is NetworkResult.Success -> {
val item = response.data
emptyItem.setProperties(item)
}
}
}
}
is NetworkResult.Error -> return#withContext result
}
return#withContext NetworkResult.Success(itemList)
}

I would like to propose you to use async to process every item separately:
suspend operator fun invoke(feedType: String): NetworkResult<List<MyItem>> = withContext(Dispatchers.IO) {
when (val result = repository.fetchItems()) { // 1
is NetworkResult.Success -> {
result.data
.map { async { fetchItemData(it) } } // 2
.awaitAll() // 3
NetworkResult.Success(result.data)
}
is NetworkResult.Error -> result
}
}
private suspend fun fetchItemData(item: MyItem) {
val response = repository.fetchItem(item.id)
if (response is NetworkResult.Success) {
item.setProperties(response.data)
}
}
In this code, at first, we make a call to fetchItems to get the items ids (1). Then we make a call to fetchItem for every item at the same time (2). It can be easily done with coroutines and async. Then we wait until all data will be fetched (3).

How to perform call sequence to a REST API in Android App?

I'm having a hard time making a call to my api. I'm using Reactivex with kotlin and Flowables. My API returns a list of items if the date I passed by the "If-Modified_since" header is less than the last update.
If there is no update I get as an app return android app a 304 error.
I need to do the following procedure.
1-> I make a call to the api
2-> If the call is successful, save the list in Realm and return to the viewmodel
3-> If the error is 304, I perform a cache search (Realm) of the items
4-> If it is another error, I return the error normally for the ViewModel
Here is the code below, but I'm not sure if it's that way.
override fun getTickets(eventId: String): Flowable<List<Ticket>> {
return factory
.retrieveRemoteDataStore()
.getTickets(eventId)
.map {
saveTickets(it)
it
}.onErrorResumeNext { t: Throwable ->
if (t is HttpException && t.response().code() == 304) {
factory.retrieveCacheDataStore().getTickets(eventId)
} else
//Should return error
}
The question is, what is the best way to do this?
Thank you.

I'm going to assume, that you're using Retrofit. If that's the case, then you could wrap your getTickets call in Single<Response<SomeModel>>. This way, on first map you can check the errorcode, something among the lines of:
...getTickets(id)
.map{ response ->
when {
response.isSuccessful && response.body!=null -> {
saveTickets(it)
it
}
!response.isSuccessful && response.errorCode() == 304 -> {
factory.retrieveCacheDataStore().getTickets(eventId)
}
else -> throw IOException()
}
}
This could of course be made pretty using standard/extension functions but wanted to keep it simple for readability purposes.
Hope this helps!

Most of my comments are my explanations.
data class Ticket(val id:Int) {
companion object {
fun toListFrom(jsonObject: JSONObject): TICKETS {
/**do your parsing of data transformation here */
return emptyList()
}
}
}
typealias TICKETS = List<Ticket>
class ExampleViewModel(): ViewModel() {
private var error: BehaviorSubject<Throwable> = BehaviorSubject.create()
private var tickets: BehaviorSubject<TICKETS> = BehaviorSubject.create()
/**public interfaces that your activity or fragment talk to*/
fun error(): Observable<Throwable> = this.error
fun tickets(): Observable<TICKETS> = this.tickets
fun start() {
fetch("http://api.something.com/v1/tickets/")
.subscribeOn(Schedulers.io())
.onErrorResumeNext { t: Throwable ->
if (t.message == "304") {
get(3)
} else {
this.error.onNext(t)
/** this makes the chain completed gracefuly without executing flatMap or any other operations*/
Observable.empty()
}
}
.flatMap(this::insertToRealm)
.subscribe(this.tickets)
}
private fun insertToRealm(tickets: TICKETS) : Observable<TICKETS> {
/**any logic here is mainly to help you save into Realm**/
/** I think realm has the option to ignore items that are already in the db*/
return Observable.empty()
}
private fun get(id: Int): Observable<TICKETS> {
/**any logic here is mainly to help you fetch from your cache**/
return Observable.empty()
}
private fun fetch(apiRoute: String): Observable<TICKETS> {
/**
* boilerplate code
wether you're using Retrofit or Okhttp, that's the logic you
should try to have
* */
val status: Int = 0
val rawResponse = ""
val error: Throwable? = null
val jsonResponse = JSONObject(rawResponse)
return Observable.defer {
if (status == 200) {
Observable.just(Ticket.toListFrom(jsonResponse))
}
else if (status == 304) {
Observable.error<TICKETS>(Throwable("304"))
}
else {
Observable.error<TICKETS>(error)
}
}
}
override fun onCleared() {
super.onCleared()
this.error = BehaviorSubject.create()
this.tickets = BehaviorSubject.create()
}
}