Develop Reference

Observe callback is not being triggered with Kotlin coroutines Flow and LiveData?

I'm new to Android development and trying to understand Coroutines and LiveData from various example projects. I have currently setup a function to call my api when the user has input a username and password. However after 1 button press, the app seems to jam and I can't make another api call as if its stuck on a pending process.
This is my first android app made with a mash of ideas so please let me know where I've made mistakes!
Activity:
binding.bLogin.setOnClickListener {
val username = binding.etUsername.text.toString()
val password = binding.etPassword.text.toString()
viewModel.userClicked(username, password).observe(this, Observer {
it?.let { resource ->
when (resource.status) {
Status.SUCCESS -> {
print(resource.data)
}
Status.ERROR -> {
print(resource.message)
}
Status.LOADING -> {
// loader stuff
}
}
}
})
}
ViewModel:
fun userClicked(username: String, password: String) = liveData(dispatcherIO) {
viewModelScope.launch {
emit(Resource.loading(data = null))
try {
userRepository.login(username, password).apply {
emit(Resource.success(null))
}
} catch (exception: Exception) {
emit(Resource.error(exception.message ?: "Error Occurred!", data = null))
}
}
}
Repository:
#WorkerThread
suspend fun login(
username: String,
password: String
): Flow<Resource<String?>> {
return flow {
emit(Resource.loading(null))
api.login(LoginRequest(username, password)).apply {
this.onSuccessSuspend {
data?.let {
prefs.apiToken = it.key
emit(Resource.success(null))
}
}
}.onErrorSuspend {
emit(Resource.error(message(), null))
}.onExceptionSuspend {
emit(Resource.error(message(), null))
}
}.flowOn(dispatcherIO)
}
API:
suspend fun login(#Body request: LoginRequest): ApiResponse<Auth>

You don't need to launch a coroutine in liveData builder, it is already suspend so you can call suspend functions there:
fun userClicked(username: String, password: String) = liveData(dispatcherIO) {
emit(Resource.loading(data = null))
try {
userRepository.login(username, password).apply {
emit(Resource.success(null))
}
} catch (exception: Exception) {
emit(Resource.error(exception.message ?: "Error Occurred!", data = null))
}
}
If you want to use LiveDate with Flow you can convert Flow to LiveData object using asLiveData function:
fun userClicked(username: String, password: String): LiveData<Resource<String?>> {
return userRepository.login(username, password).asLiveData()
}
But I wouldn't recommend to mix up LiveData and Flow streams in the project. I suggest to use only Flow.
Using only Flow:
// In ViewModel:
fun userClicked(username: String, password: String): Flow<Resource<String?>> {
return userRepository.login(username, password)
}
// Activity
binding.bLogin.setOnClickListener {
val username = binding.etUsername.text.toString()
val password = binding.etPassword.text.toString()
lifecycleScope.launch {
viewModel.userClicked(username, password).collect { resource ->
when (resource.status) {
Status.SUCCESS -> {
print(resource.data)
}
Status.ERROR -> {
print(resource.message)
}
Status.LOADING -> {
// loader stuff
}
}
}
}
}
Remove suspend keyword from the login function in Repository.
lifecycleScope docs.

FirebaseAuth - how can I wait for value

I use FirebaseAuth for registration new user
class FirebaseAuthenticationServiceImpl(): FirebaseAuthenticationService {
override fun registerWithEmailAndPassword(email: String, password: String): Boolean {
val registration = FirebaseAuth.getInstance().createUserWithEmailAndPassword(email, password)
.addOnSuccessListener {
println(it.additionalUserInfo?.providerId.toString())
}.addOnFailureListener {
println(it.message.toString())
}
return registration.isSuccessful
}
}
I call function above and every time I get false. After some time I get true
coroutineScope {
try {
if (firebaseService.registerWithEmailAndPassword(email, password)) {
openHomeActivity.offer(Unit)
} else {}
} catch (e: Exception) {}
}
How can I wait for uth result (success/failure) and afer that get that value?

Where is FirebaseAuthenticationService from? Do you need it? The official getting started guide just uses Firebase.auth. With this, you can authenticate using the await() suspend function instead of using the callback approach.
// In a coroutine:
val authResult = Firebase.auth.registerWithEmailAndPassword(email, password).await()
val user: FirebaseUser = authResult.user
if (user != null) {
openHomeActivity.offer(Unit)
} else {
// authentication failed
}

If you are using coroutines you can use suspendCoroutine which is perfect bridge between traditional callbacks and coroutines as it gives you access to the Continuation<T> object, example with a convenience extension function for Task<R> objects :
scope.launch {
val registrationResult = suspendCoroutine { cont -> cont.suspendTask(FirebaseAuth.getInstance().createUserWithEmailAndPassword(email, password) }
}
private fun <R> Continuation<R>.suspendTask(task: Task<R>) {
task.addOnSuccessListener { this.success(it) }
.addOnFailureListener { this.failure(it) }
}
private fun <R> Continuation<R>.success(r : R) = resume(r)
private fun <R> Continuation<R>.failure(t : Exception) = resumeWithException(t)

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()
}

callbackFlow not returning anything android kotlin

I want to implement firebase realtime database with coroutines, so I need to use flow because firebase just accept callbacks. the problem is the .collect{} block never gets executed
here is my code
#ExperimentalCoroutinesApi
override suspend fun getProduct(barcode: String): ProductItem? {
return withContext(Dispatchers.Default) {
println("Hi")
var item: ProductItem? = null
productFlow(barcode).collect {
//this never gets called
print("Getting product")
item = it
}
println("Ending product request ${item?.name}")
Log.i("GetProduct",item?.name)
item
}
}
#ExperimentalCoroutinesApi
private fun productFlow(barcode: String): Flow<ProductItem?> = callbackFlow {
val database = FirebaseDatabase.getInstance()
val productRef = database.getReference("products/$barcode")
val callback = object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
for(snapshot in dataSnapshot.children){
Log.i("Source", snapshot.value.toString())
}
val product = dataSnapshot.getValue(ProductItem::class.java)
Log.i("Source",product?.name) //everything is good until here
sendBlocking(dataSnapshot.getValue(ProductItem::class.java)) //after this i dont get anything on the collect{} block
}
override fun onCancelled(databaseError: DatabaseError) {
println("cancelling")
sendBlocking(null)
}
}
try {
productRef.addListenerForSingleValueEvent(callback)
} catch (e: FirebaseException) {
println("Firebase exception")
sendBlocking(null)
}
awaitClose{
println("Closing")
productRef.removeEventListener(callback)
}
}

First I would suggest to use the catch method to check if there is an error or not. Second, for callbackflow I remember using offer() instead of sendBlocking

Coroutin To Perform task

hi this is my user repository
class UserRepository(private val appAuth: FirebaseAuth) : SafeAuthRequest(){
suspend fun userLogin(email: String,password: String) : AuthResult{
return authRequest { appAuth.signInWithEmailAndPassword(email,password)}
}
}
this is the SafeAuthRequest class
open class SafeAuthRequest {
suspend fun<T: Any> authRequest(call : suspend () -> Task<T>) : T{
val task = call.invoke()
if(task.isSuccessful){
return task.result!!
}
else{
val error = task.exception?.message
throw AuthExceptions("$error\nInvalid email or password")
}
}
}
calling above things like that
/** Method to perform login operation with custom */
fun onClickCustomLogin(view: View){
authListener?.onStarted()
Coroutines.main {
try {
val authResult = repository.userLogin(email!!,password!!)
authListener?.onSuccess()
}catch (e : AuthExceptions){
authListener?.onFailure(e.message!!)
}
}
}
and my authListener like this
interface AuthListener {
fun onStarted()
fun onSuccess()
fun onFailure(message: String)
}
I am getting an error as the task is not completed
is the correct way to implement the task

I'm using MVVM architectural pattern, so the example I'm going to provide is called from my ViewModel class, that means I have access to viewModelScope. If you want to run a similar code on Activity class, you have to use the Coroutines scope available for your Activity, for example:
val uiScope = CoroutineScope(Dispatchers.Main)
uiScope.launch {...}
Answering your question, what I've done to retrieve login from user repository is this:
//UserRepository.kt
class UserRepository(private val appAuth: FirebaseAuth) {
suspend fun userLogin(email: String, password: String) : LoginResult{
val firebaseUser = appAuth.signInWithEmailAndPassword(email, password).await() // Do not forget .await()
return LoginResult(firebaseUser)
}
}
LoginResult is a wrapper class of firebase auth response.
//ClassViewModel.kt
class LoginFirebaseViewModel(): ViewModel(){
private val _loginResult = MutableLiveData<LoginResult>()
val loginResult: LiveData<LoginResult> = _loginResult
fun login() {
viewModelScope.launch {
try {
repository.userLogin(email!!,password!!).let {
_loginResult.value = it
}
} catch (e: FirebaseAuthException) {
// Do something on firebase exception
}
}
}
}
The code on Activity class would be like this:
// Function inside Activity
fun onClickCustomLogin(view: View){
val uiScope = CoroutineScope(Dispatchers.Main)
uiScope.launch {
try {
repository.userLogin(email!!,password!!).let {
authResult = it
}
}catch (e : FirebaseAuthException){
// Do something on firebase exception
}
}
}
One of the main benefits of using Coroutines is that you convert asynchronous code in sequential one. That means you don't need listeners or callbacks.
I hope this help you