My Worker(for API call) starts from Service and I want to completion event send into Service class.
What should be best approach?
Calling from service:
PeriodicWorkRequest request = new PeriodicWorkRequest
.Builder(Worker.class, Constants.REPEAT_INTERVAL, TimeUnit.MINUTES)
.addTag(TAG)
.setConstraints(new Constraints.Builder().setRequiredNetworkType(NetworkType.CONNECTED).build())
.build();
WorkManager.getInstance(getApplicationContext()).enqueue(request);
Calling from WorkManager:
override fun doWork(): Result {
// API call
return Result.success()
}
Okay so what I would do is I would create common object for both Worker and Service class and utilize Observer pattern. This WorkObserver object would behave as a proxy between Service and Worker. Using Koin for example, it would look something like that:
class MyWorker: Worker(), KoinComponent {
private val workObserver: WorkObserver by inject()
override fun doWork(): Result {
val result = api.call().execute()
if(result.isSuccessful) {
workObserver.notifySuccess()
return Result.success()
} else {
workObserver.notifyError()
return Result.failure()
}
}
}
class MyService: Service(), KoinComponent {
private val workObserver: WorkObserver by inject()
override fun onCreate() {
workObserver.setOnResultListener { result ->
if(result) {
//do something
} else {
// do something else
}
}
override fun onDestroy() {
workObserver.setOnResultListener(null)
}
}
class WorkObserver {
private var onResultListener: ((Result) -> Unit)? = null
fun setOnResultListener(listener: ((Result) -> Unit)?) {
this.onResultListener = listener
}
fun notifySuccess() {
this.onResultListener?.invoke(true)
}
fun notifyError() {
this.onResultListener?.invoke(false)
}
}
Of course you can use other DI tools for that, you can have a list of listeners and remove particular ones, you can pass any other object through the listener in WorkObserver with the payload you need. I just created a simple boolean passing
For that simple case however if you don't want to use DI, simple Object would do the work. However when your codebase grows and you are dealing with multithreading issues, or even accessing this object in other parts of the application it may lead to problems. I am using it only to pass information between objects, I don't recommend using it for storing data etc:
class MyWorker: Worker() {
override fun doWork(): Result {
val result = api.call().execute()
if(result.isSuccessful) {
WorkObserver.notifySuccess()
return Result.success()
} else {
WorkObserver.notifyError()
return Result.failure()
}
}
}
class MyService: Service() {
override fun onCreate() {
WorkObserver.setOnResultListener { result ->
if(result) {
//do something
} else {
// do something else
}
}
override fun onDestroy() {
WorkObserver.setOnResultListener(null)
}
}
object WorkObserver {
private var onResultListener: ((Result) -> Unit)? = null
fun setOnResultListener(listener: ((Result) -> Unit)?) {
this.onResultListener = listener
}
fun notifySuccess() {
this.onResultListener?.invoke(true)
}
fun notifyError() {
this.onResultListener?.invoke(false)
}
}
Related
Context
I started working on a new project and I've decided to move from RxJava to Kotlin Coroutines. I'm using an MVVM clean architecture, meaning that my ViewModels communicate to UseCases classes, and these UseCases classes use one or many Repositories to fetch data from network.
Let me give you an example. Let's say we have a screen that is supposed to show the user profile information. So we have the UserProfileViewModel:
#HiltViewModel
class UserProfileViewModel #Inject constructor(
private val getUserProfileUseCase: GetUserProfileUseCase
) : ViewModel() {
sealed class State {
data SuccessfullyFetchedUser(
user: ExampleUser
) : State()
}
// ...
val state = SingleLiveEvent<UserProfileViewModel.State>()
// ...
fun fetchUserProfile() {
viewModelScope.launch {
// ⚠️ We trigger the use case to fetch the user profile info
getUserProfileUseCase()
.collect {
when (it) {
is GetUserProfileUseCase.Result.UserProfileFetched -> {
state.postValue(State.SuccessfullyFetchedUser(it.user))
}
is GetUserProfileUseCase.Result.ErrorFetchingUserProfile -> {
// ...
}
}
}
}
}
}
The GetUserProfileUseCase use case would look like this:
interface GetUserProfileUseCase {
sealed class Result {
object ErrorFetchingUserProfile : Result()
data class UserProfileFetched(
val user: ExampleUser
) : Result()
}
suspend operator fun invoke(email: String): Flow<Result>
}
class GetUserProfileUseCaseImpl(
private val userRepository: UserRepository
) : GetUserProfileUseCase {
override suspend fun invoke(email: String): Flow<GetUserProfileUseCase.Result> {
// ⚠️ Hit the repository to fetch the info. Notice that if we have more
// complex scenarios, we might require zipping repository calls together, or
// flatmap responses.
return userRepository.getUserProfile().flatMapMerge {
when (it) {
is ResultData.Success -> {
flow { emit(GetUserProfileUseCase.Result.UserProfileFetched(it.data.toUserExampleModel())) }
}
is ResultData.Error -> {
flow { emit(GetUserProfileUseCase.Result.ErrorFetchingUserProfile) }
}
}
}
}
}
The UserRepository repository would look like this:
interface UserRepository {
fun getUserProfile(): Flow<ResultData<ApiUserProfileResponse>>
}
class UserRepositoryImpl(
private val retrofitApi: RetrofitApi
) : UserRepository {
override fun getUserProfile(): Flow<ResultData<ApiUserProfileResponse>> {
return flow {
val response = retrofitApi.getUserProfileFromApi()
if (response.isSuccessful) {
emit(ResultData.Success(response.body()!!))
} else {
emit(ResultData.Error(RetrofitNetworkError(response.code())))
}
}
}
}
And finally, the RetrofitApi and the response class to model the backend API response would look like this:
data class ApiUserProfileResponse(
#SerializedName("user_name") val userName: String
// ...
)
interface RetrofitApi {
#GET("api/user/profile")
suspend fun getUserProfileFromApi(): Response<ApiUserProfileResponse>
}
Everything has been working fine so far, but I've started to run into some issues when implementing more complex features.
For example, there's a use case where I need to (1) post to a POST /send_email_link endpoint when the user first signs in, this endpoint will check if the email that I send in the body already exists, if it doesn't it will return a 404 error code, and (2) if everything goes okay, I'm supposed to hit a POST /peek endpoint that will return some info about the user account.
This is what I've implemented so far for this UserAccountVerificationUseCase:
interface UserAccountVerificationUseCase {
sealed class Result {
object ErrorVerifyingUserEmail : Result()
object ErrorEmailDoesNotExist : Result()
data class UserEmailVerifiedSuccessfully(
val canSignIn: Boolean
) : Result()
}
suspend operator fun invoke(email: String): Flow<Result>
}
class UserAccountVerificationUseCaseImpl(
private val userRepository: UserRepository
) : UserAccountVerificationUseCase {
override suspend fun invoke(email: String): Flow<UserAccountVerificationUseCase.Result> {
return userRepository.postSendEmailLink().flatMapMerge {
when (it) {
is ResultData.Success -> {
userRepository.postPeek().flatMapMerge {
when (it) {
is ResultData.Success -> {
val canSignIn = it.data?.userName == "Something"
flow { emit(UserAccountVerificationUseCase.Result.UserEmailVerifiedSuccessfully(canSignIn)) }
} else {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
}
}
}
is ResultData.Error -> {
if (it.exception is RetrofitNetworkError) {
if (it.exception.errorCode == 404) {
flow { emit(UserAccountVerificationUseCase.Result.ErrorEmailDoesNotExist) }
} else {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
} else {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
}
}
}
}
}
Issue
The above solution is working as expected, if the first API call to the POST /send_email_link ever returns a 404, the use case will behave as expected and return the ErrorEmailDoesNotExist response so the ViewModel can pass that back to the UI and show the expected UX.
The problem as you can see is that this solution requires a ton of boilerplate code, I thought using Kotlin Coroutines would make things simpler than with RxJava, but it hasn't turned out like that yet. I'm quite sure that this is because I'm missing something or I haven't quite learned how to use Flow properly.
What I've tried so far
I've tried to change the way I emit the elements from the repositories, from this:
...
override fun getUserProfile(): Flow<ResultData<ApiUserProfileResponse>> {
return flow {
val response = retrofitApi.getUserProfileFromApi()
if (response.isSuccessful) {
emit(ResultData.Success(response.body()!!))
} else {
emit(ResultData.Error(RetrofitNetworkError(response.code())))
}
}
}
...
To something like this:
...
override fun getUserProfile(): Flow<ResultData<ApiUserProfileResponse>> {
return flow {
val response = retrofitApi.getUserProfileFromApi()
if (response.isSuccessful) {
emit(ResultData.Success(response.body()!!))
} else {
error(RetrofitNetworkError(response.code()))
}
}
}
..
So I can use the catch() function like I'd with RxJava's onErrorResume():
class UserAccountVerificationUseCaseImpl(
private val userRepository: UserRepository
) : UserAccountVerificationUseCase {
override suspend fun invoke(email: String): Flow<UserAccountVerificationUseCase.Result> {
return userRepository.postSendEmailLink()
.catch { e ->
if (e is RetrofitNetworkError) {
if (e.errorCode == 404) {
flow { emit(UserAccountVerificationUseCase.Result.ErrorEmailDoesNotExist) }
} else {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
} else {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
}
.flatMapMerge {
userRepository.postPeek().flatMapMerge {
when (it) {
is ResultData.Success -> {
val canSignIn = it.data?.userName == "Something"
flow { emit(UserAccountVerificationUseCase.Result.UserEmailVerifiedSuccessfully(canSignIn)) }
} else -> {
flow { emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail) }
}
}
}
}
}
}
}
This does reduce the boilerplate code a bit, but I haven't been able to get it working because as soon as I try to run the use case like this I start getting errors saying that I shouldn't emit items in the catch().
Even if I could get this working, still, there's way too much boilerplate code here. I though doing things like this with Kotlin Coroutines would mean having much more simple, and readable, use cases. Something like:
...
class UserAccountVerificationUseCaseImpl(
private val userRepository: AuthRepository
) : UserAccountVerificationUseCase {
override suspend fun invoke(email: String): Flow<UserAccountVerificationUseCase.Result> {
return flow {
coroutineScope {
val sendLinksResponse = userRepository.postSendEmailLink()
if (sendLinksResponse is ResultData.Success) {
val peekAccount = userRepository.postPeek()
if (peekAccount is ResultData.Success) {
emit(UserAccountVerificationUseCase.Result.UserEmailVerifiedSuccessfully())
} else {
emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail)
}
} else {
if (sendLinksResponse is ResultData.Error) {
if (sendLinksResponse.error == 404) {
emit(UserAccountVerificationUseCase.Result.ErrorEmailDoesNotExist)
} else {
emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail)
}
} else {
emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail)
}
}
}
}
}
}
...
This is what I had pictured about working with Kotlin Coroutines. Ditching RxJava's zip(), contact(), delayError(), onErrorResume() and all those Observable functions in favor of something more readable.
Question
How can I reduce the amount of boilerplate code and make my use cases look more Coroutine-like?
Notes
I know some people just call the repositories directly from the ViewModel layer, but I like having this UseCase layer in the middle so I can contain all the code related to switching streams and handling errors here.
Any feedback is appreciated! Thanks!
Edit #1
Based on #Joffrey response, I've changed the code so it works like this:
The Retrofit API layer keeps returning suspendable function.
data class ApiUserProfileResponse(
#SerializedName("user_name") val userName: String
// ...
)
interface RetrofitApi {
#GET("api/user/profile")
suspend fun getUserProfileFromApi(): Response<ApiUserProfileResponse>
}
The repository now returns a suspendable function and I've removed the Flow wrapper:
interface UserRepository {
suspend fun getUserProfile(): ResultData<ApiUserProfileResponse>
}
class UserRepositoryImpl(
private val retrofitApi: RetrofitApi
) : UserRepository {
override suspend fun getUserProfile(): ResultData<ApiUserProfileResponse> {
val response = retrofitApi.getUserProfileFromApi()
return if (response.isSuccessful) {
ResultData.Success(response.body()!!)
} else {
ResultData.Error(RetrofitNetworkError(response.code()))
}
}
}
The use case keeps returning a Flow since I might also plug calls to a Room DB here:
interface GetUserProfileUseCase {
sealed class Result {
object ErrorFetchingUserProfile : Result()
data class UserProfileFetched(
val user: ExampleUser
) : Result()
}
suspend operator fun invoke(email: String): Flow<Result>
}
class GetUserProfileUseCaseImpl(
private val userRepository: UserRepository
) : GetUserProfileUseCase {
override suspend fun invoke(email: String): Flow<GetUserProfileUseCase.Result> {
return flow {
val userProfileResponse = userRepository.getUserProfile()
when (userProfileResponse) {
is ResultData.Success -> {
emit(GetUserProfileUseCase.Result.UserProfileFetched(it.toUserModel()))
}
is ResultData.Error -> {
emit(GetUserProfileUseCase.Result.ErrorFetchingUserProfile)
}
}
}
}
}
This looks much more clean. Now, applying the same thing to the UserAccountVerificationUseCase:
interface UserAccountVerificationUseCase {
sealed class Result {
object ErrorVerifyingUserEmail : Result()
object ErrorEmailDoesNotExist : Result()
data class UserEmailVerifiedSuccessfully(
val canSignIn: Boolean
) : Result()
}
suspend operator fun invoke(email: String): Flow<Result>
}
class UserAccountVerificationUseCaseImpl(
private val userRepository: UserRepository
) : UserAccountVerificationUseCase {
override suspend fun invoke(email: String): Flow<UserAccountVerificationUseCase.Result> {
return flow {
val sendEmailLinkResponse = userRepository.postSendEmailLink()
when (sendEmailLinkResponse) {
is ResultData.Success -> {
val peekResponse = userRepository.postPeek()
when (peekResponse) {
is ResultData.Success -> {
val canSignIn = peekResponse.data?.userName == "Something"
emit(UserAccountVerificationUseCase.Result.UserEmailVerifiedSuccessfully(canSignIn)
}
else -> {
emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail)
}
}
}
is ResultData.Error -> {
if (sendEmailLinkResponse.isNetworkError(404)) {
emit(UserAccountVerificationUseCase.Result.ErrorEmailDoesNotExist)
} else {
emit(UserAccountVerificationUseCase.Result.ErrorVerifyingUserEmail)
}
}
}
}
}
}
This looks much more clean and it works perfectly. I still wonder if there's any more room for improvement here.
The most obvious problem I see here is that you're using Flow for single values instead of suspend functions.
Coroutines makes the single-value use case much simpler by using suspend functions that return plain values or throw exceptions. You can of course also make them return Result-like classes to encapsulate errors instead of actually using exceptions, but the important part is that with suspend functions you are exposing a seemingly synchronous (thus convenient) API while still benefitting from asynchronous runtime.
In the provided examples you're not subscribing for updates anywhere, all flows actually just give a single element and complete, so there is no real reason to use flows and it complicates the code. It also makes it harder to read for people used to coroutines because it looks like multiple values are coming, and potentially collect being infinite, but it's not the case.
Each time you write flow { emit(x) } it should just be x.
Following the above, you're sometimes using flatMapMerge and in the lambda you create flows with a single element. Unless you're looking for parallelization of the computation, you should simply go for .map { ... } instead. So replace this:
val resultingFlow = sourceFlow.flatMapMerge {
if (something) {
flow { emit(x) }
} else {
flow { emit(y) }
}
}
With this:
val resultingFlow = sourceFlow.map { if (something) x else y }
I have the following:
interface CartRepository {
fun getCart(): Flow<CartState>
}
interface ProductRepository {
fun getProductByEan(ean: String): Flow<Either<ServerError, Product?>>
}
class ScanViewModel(
private val productRepository: ProductRepository,
private val cartRepository: CartRepository
) :
BaseViewModel<ScanUiState>(Initial) {
fun fetchProduct(ean: String) = viewModelScope.launch {
setState(Loading)
productRepository
.getProductByEan(ean)
.combine(cartRepository.getCart(), combineToGridItem())
.collect { result ->
when (result) {
is Either.Left -> {
sendEvent(Error(R.string.error_barcode_product_not_found, null))
setState(Initial)
}
is Either.Right -> {
setState(ProductUpdated(result.right))
}
}
}
}
}
When a user scans a barcode fetchProduct is being called. Every time a new coroutine is being set up. And after a while, there are many running in the background and the combine is triggered when the cart state is updated on all of them, which can cause errors.
I want to cancel all old coroutines and only have the latest call running and update on cart change.
I know I can do the following by saving the job and canceling it before starting a new one. But is this really the way to go? Seems like I'm missing something.
var searchJob: Job? = null
private fun processImage(frame: Frame) {
barcodeScanner.process(frame.toInputImage(this))
.addOnSuccessListener { barcodes ->
barcodes.firstOrNull()?.rawValue?.let { ean ->
searchJob?.cancel()
searchJob = viewModel.fetchProduct(ean)
}
}
.addOnFailureListener {
Timber.e(it)
messageMaker.showError(
binding.root,
getString(R.string.unknown_error)
)
}
}
I could also have a MutableSharedFlow in my ViewModel to make sure the UI only react to the last product the user has been fetching:
private val productFlow = MutableSharedFlow<Either<ServerError, Product?>>(replay = 1)
init {
viewModelScope.launch {
productFlow.combine(
mycroftRepository.getCart(),
combineToGridItem()
).collect { result ->
when (result) {
is Either.Right -> {
setState(ProductUpdated(result.right))
}
else -> {
sendEvent(Error(R.string.error_barcode_product_not_found, null))
setState(Initial)
}
}
}
}
}
fun fetchProduct(ean: String) = viewModelScope.launch {
setState(Loading)
repository.getProductByEan(ean).collect { result ->
productFlow.emit(result)
}
}
What's considered best practice handling this scenario?
I can't think of a simpler pattern for cancelling any previous Job when starting a new one.
If you're concerned about losing your stored job reference on screen rotation (you probably won't since Fragment instances are typically reused on rotation), you can move Job storage and cancellation into the ViewModel:
private var fetchProductJob: Job? = null
fun fetchProduct(ean: String) {
fetchProductJob?.cancel()
fetchProductJob = viewModelScope.launch {
//...
}
}
If you're repeatedly using this pattern, you could create a helper class like this. Not sure if there's a better way.
class SingleJobPipe(val scope: CoroutineScope) {
private var job: Job? = null
fun launch(
context: CoroutineContext = EmptyCoroutineContext,
start: CoroutineStart = CoroutineStart.DEFAULT,
block: suspend CoroutineScope.() -> Unit
): Job = synchronized(this) {
job?.cancel()
scope.launch(context, start, block).also { job = it }
}
}
// ...
private val fetchProductPipe = SingleJobPipe(viewModelScope)
fun fetchProduct(ean: String) = fetchProductPipe.launch {
//...
}
I have a flow to fetch data from database via content provider.
fun getDataFlow(): Flow<Result> {
return flow {
emit(Result.Loading)
// fetchAll() is the method to fetch data via contentResolover.query()
val results = fetchAll()
emit(Result.Success(categories))
}.catch { e ->
emit(Result.Error(e))
}
}
So how to trigger refetching data when ContentProvider data changed (onChange get called)?
val contentObserver = object : ContentObserver(null) {
override fun onChange(selfChange: Boolean) {
super.onChange(selfChange)
}
}
you can use callback flow
#ExperimentalCoroutinesApi
fun ContentResolver.register(uri: Uri) = callbackFlow<Boolean> {
val observer = object : ContentObserver(null) {
override fun onChange(selfChange: Boolean) {
trySend(selfChange)
}
}
registerContentObserver(uri, false, observer)
invokeOnClose {
unregisterContentObserver(observer)
}
}
then u can do something like this
getDataFlow().combine(ContentResolver.register("YOUR_URI")){data, isSelfChange ->
}
I have recently seen a weird issue that is acting as a barrier to my project.
Multiple calls to set the live data value does not invoke the observer in the view.
It seems that only the last value that was set actually invokes the Observer in the view.
Here is the code snippet for a review.
MainActivity.kt
class MainActivity : AppCompatActivity() {
private lateinit var viewModel: MainViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel = ViewModelProviders.of(this).get(MainViewModelImpl::class.java)
viewModel.state().observe(this, Observer {
onStateChange(it!!)
})
viewModel.fetchFirstThree()
}
private fun onStateChange(state: MainViewModel.State) {
when (state) {
is One -> {
show(state.data)
}
is Two -> {
show(state.data)
}
is Three -> {
show(state.data)
}
}
}
private fun show(data: String) {
Log.d("Response", data)
}
}
MainViewModel.kt
abstract class MainViewModel : ViewModel() {
sealed class State {
data class One(val data: String) : State()
data class Two(val data: String) : State()
data class Three(val data: String) : State()
}
abstract fun state(): LiveData<State>
abstract fun fetchFirstThree()
}
MainViewModelImpl.kt
class MainViewModelImpl : MainViewModel() {
private val stateLiveData: MediatorLiveData<State> = MediatorLiveData()
override fun state(): LiveData<State> = stateLiveData
override fun fetchFirstThree() {
stateLiveData.value = State.One("One")
stateLiveData.value = State.Two("Two")
stateLiveData.value = State.Three("Three")
}
}
Expected output:
Response: One
Response: Two
Response: Three
Actual Output:
Response: Three
As per the output above, the Observer is not being called for the first two values.
I did some science, re-implementing LiveData and MutableLiveData to log out some data.
Check the source code here.
setValue value=Test1
dispatchingValue mDispatchingValue=false mDispatchInvalidated=false
considerNotify
Returned at !observer.active
setValue value=Test2
dispatchingValue mDispatchingValue=false mDispatchInvalidated=false
considerNotify
Returned at !observer.active
setValue value=Test3
dispatchingValue mDispatchingValue=false mDispatchInvalidated=false
considerNotify
Returned at !observer.active
dispatchingValue mDispatchingValue=false mDispatchInvalidated=false
considerNotify
ITEM: Test3
It looks like the observer hasn't reached an active state when you send the initial values.
private void considerNotify(LifecycleBoundObserver observer) {
// <-- Three times it fails here. This means that your observer wasn't ready for any of them.
if (!observer.active) {
return;
}
Once the observer reaches an active state, it sends the last set value.
void activeStateChanged(boolean newActive) {
if (newActive == active) {
return;
}
active = newActive;
boolean wasInactive = LiveData.this.mActiveCount == 0;
LiveData.this.mActiveCount += active ? 1 : -1;
if (wasInactive && active) {
onActive();
}
if (LiveData.this.mActiveCount == 0 && !active) {
onInactive();
}
if (active) {
// <--- At this point you are getting a call to your observer!
dispatchingValue(this);
}
}
I had such issue too.
To resolve it was created custom MutableLiveData, that contains a queue of posted values and will notify observer for each value.
You can use it the same way as usual MutableLiveData.
open class MultipleLiveEvent<T> : MutableLiveData<T>() {
private val mPending = AtomicBoolean(false)
private val values: Queue<T> = LinkedList()
#MainThread
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
if (hasActiveObservers()) {
Log.w(this::class.java.name, "Multiple observers registered but only one will be notified of changes.")
}
// Observe the internal MutableLiveData
super.observe(owner, { t: T ->
if (mPending.compareAndSet(true, false)) {
observer.onChanged(t)
//call next value processing if have such
if (values.isNotEmpty())
pollValue()
}
})
}
override fun postValue(value: T) {
values.add(value)
pollValue()
}
private fun pollValue() {
value = values.poll()
}
#MainThread
override fun setValue(t: T?) {
mPending.set(true)
super.setValue(t)
}
/**
* Used for cases where T is Void, to make calls cleaner.
*/
#Suppress("unused")
#MainThread
fun call() {
value = null
}
}
You could use custom LiveData like this:
class ActiveMutableLiveData<T> : MutableLiveData<T>() {
private val values: Queue<T> = LinkedList()
private var isActive: Boolean = false
override fun onActive() {
isActive = true
while (values.isNotEmpty()) {
setValue(values.poll())
}
}
override fun onInactive() {
isActive = false
}
override fun setValue(value: T) {
if (isActive) {
super.setValue(value)
} else {
values.add(value)
}
}
}
FWIW I had the same problem but solved it like this...
I originally had some code similar to this...
private fun updateMonth(month: Int){
updateMonth.value = UpdateMonth(month, getDaysOfMonth(month))
}
updateMonth(1)
updateMonth(2)
updateMonth(3)
I experienced the same problem as described...
But when I made this simple change....
private fun updateMonth(month: Int) {
CoroutineScope(Dispatchers.Main).launch {
updateMonth.value = UpdateMonth(month, getDaysOfMonth(month))
}
}
Presumably, each updateMonth is going onto a different thread now, so all of the updates are observed.
You should call viewModel.fetchFirstThree() after Activity's onStart() method. for example in onResume() method.
Because in LiveData the Observer is wrapped as a LifecycleBoundObserver. The field mActive set to true after onStart().
class LifecycleBoundObserver extends ObserverWrapper implements GenericLifecycleObserver {
#Override
boolean shouldBeActive() {
return mOwner.getLifecycle().getCurrentState().isAtLeast(STARTED);// return true after onStart()
}
#Override
public void onStateChanged(LifecycleOwner source, Lifecycle.Event event) {
if (mOwner.getLifecycle().getCurrentState() == DESTROYED) {
removeObserver(mObserver);
return;
}
activeStateChanged(shouldBeActive());// after onStart() change mActive to true
}
}
When the observer notify the change it calls considerNotify, before onStart it will return at !observer.mActive
private void considerNotify(ObserverWrapper observer) {
if (!observer.mActive) {// called in onCreate() will return here.
return;
}
if (!observer.shouldBeActive()) {
observer.activeStateChanged(false);
return;
}
if (observer.mLastVersion >= mVersion) {
return;
}
observer.mLastVersion = mVersion;
//noinspection unchecked
observer.mObserver.onChanged((T) mData);
}
I have this issue ;)
I'm trying to call this usecase, which at the end returns an Observable.
But, despite using schedulers, constantly is being invoked on the main thread. I don't know why:
It looks like this:
class MainViewModel #Inject constructor(private val loadNewsUseCase: LoadNews) : Model {
override fun loadNews() {
loadNewsUseCase.execute(NewsObserver(), "")
}
override fun dispose() {
loadNewsUseCase.dispose()
}
}
class NewsObserver : DisposableObserver<Result>() {
override fun onComplete() {
Log.i("TAG", "")
}
override fun onNext(t: Result) {
Log.i("TAG", "")
}
override fun onError(e: Throwable) {
Log.i("TAG", "")
}
}
-
abstract class UseCase<T, in P>(
private val computationThreadExecutor: ComputationThreadExecutor,
private val mainThreadExecutor: MainThreadExecutor,
private val compositeDisposable: CompositeDisposable = CompositeDisposable()
) {
abstract fun createUseCase(params: P): Observable<T>
fun execute(disposableObserver: DisposableObserver<T>, params: P) {
requireNotNull(disposableObserver)
val observable = createUseCase(params)
.subscribeOn(Schedulers.newThread())
.observeOn(mainThreadExecutor.getThread())
val disposable = observable.subscribeWith(disposableObserver)
addDisposable(disposable)
}
private fun addDisposable(disposable: Disposable) {
requireNotNull(disposable)
compositeDisposable.add(disposable)
}
fun dispose() {
!compositeDisposable.isDisposed.apply { compositeDisposable.dispose() }
}
}
UseCase concrete implementation uses DataService to fetch data from api, which looks like this:
open class NewsDataService(private val newsDataProvider: NewsDataProvider) : NewsService {
override fun loadNews(): Observable<Result> {
return Observable.just(newsDataProvider.fetchData())
}
}
Inside NewsDataProvider is normal sync retrofit call.
Problem is, that from every begininning useCase is invoked in the mainThread(). Shouldn't be called in a new thread?
Replace
Observable.just(foo)
with something like
Observable.fromCallable(() -> foo)
Observable.just() creates an observable from the supplied values and you're computing the value on the main thread. fromCallable() takes in a callback that can be invoked on your subscription thread.
Make fetchData return an Observable<Result> (or potentially Single but that would require wider updates in your code). Retrofit supports RxJava.