I am trying to use Android Paging with ItemKeyedDataSource. Network call fetches list of items but my pagedList is not getting updated with the list.
`override fun loadInitial(
params: LoadInitialParams<String>,
callback: LoadInitialCallback<InteractionEntity>
) {
Timber.d("load Initial called")
interactionsRepository.getInteractions(params.requestedLoadSize,reviewFiltersEntity.locationId,reviewFiltersEntity.startDate,
reviewFiltersEntity.endDate,reviewFiltersEntity.siteUrls,reviewFiltersEntity.ratingFilters,reviewFiltersEntity.responseStatus,null,null)
.subscribe(object: Observer<List<InteractionEntity>>{
override fun onComplete() {
Timber.d("getInteractions complete")
}
override fun onSubscribe(d: Disposable) {
Timber.d("getInteractions subscribed ")
}
override fun onNext(t: List<InteractionEntity>) {
Timber.d("getInteractions onNext "+t.size)
callback.onResult(t)
}
override fun onError(e: Throwable) {
Timber.d("getInteractions error "+e.message)
}
})
}`
DataSourceFactory
'var interactionDataSourceLiveData = MutableLiveData<InteractionDataSource>()
override fun create(): DataSource<String, InteractionEntity> {
val interactionDataSource = InteractionDataSource(interactionsRepository,locationsRepository,reviewFiltersEntity)
interactionDataSourceLiveData.postValue(interactionDataSource)
return interactionDataSource
}'
ViewModel
'fun loadInteractions(reviewFiltersEntity: ReviewFiltersEntity){
interactionDataSourceFactory = InteractionDataSourceFactory(interactionsRepository,locationsRepository,reviewFiltersEntity)
interactionDataSourceLiveData = interactionDataSourceFactory?.interactionDataSourceLiveData
var config = PagedList.Config.Builder()
.setEnablePlaceholders(true)
.setInitialLoadSizeHint(10)
.setPageSize(20)
.setPrefetchDistance(4)
.build()
interactionsPagedList = LivePagedListBuilder<String, InteractionEntity>(interactionDataSourceFactory!!,config)
.setFetchExecutor(executor)
.build()
}'
Activity
'interactionPagingViewModel?.loadInteractions(reviewFiltersEntity)
interactionPagingViewModel?.interactionsPagedList?.observe(this, Observer {
Timber.d("interaction paged list changed ")
if(!it.isNullOrEmpty()){
Timber.d("fetched interactions in paging "+it.size)
adapter.submitList(it)
}else{
showError(R.string.error_fetching_reviews)
}
})'
I can see the list fetched in loadInitial but I do not see the same onChanged of Observer above.
Any idea What could be wrong?
Found the solution. The problem was DataSource of Android Paging required the api calls to be synchronous. Since the thread of data source and that of api call were different the data source was unable to post the result fetched by api call. So Instead of subscribe, I called blockingFirst() and it worked.
Related
I am trying to retrieve the base url from my proto datastore to be used to initialize my ktor client instance I know how to get the data from the datastore but I don't know how to block execution until that value is received so the client can be initialized with the base url
So my ktor client service asks for a NetworkURLS class which has a method to return the base url
Here is my property to retrieve terminalDetails from my proto datastore
val getTerminalDetails: Flow<TerminalDetails> = cxt.terminalDetails.data
.catch { e ->
if (e is IOException) {
Log.d("Error", e.message.toString())
emit(TerminalDetails.getDefaultInstance())
} else {
throw e
}
}
Normally when I want to get the values I would do something like this
private fun getTerminalDetailsFromStore() {
try {
viewModelScope.launch(Dispatchers.IO) {
localRepository.getTerminalDetails.collect {
_terminalDetails.value = it
}
}
} catch(e: Exception) {
Log.d("AdminSettingsViewModel Error", e.message.toString()) // TODO: Handle Error Properly
}
}
but in my current case what I am looking to do is return terminalDetails.backendHost from a function and that where the issue comes in I know I need to use a coroutine scope to retrieve the value so I don't need to suspend the function but how to a prevent the function returning until the coroutine scope has finished?
I have tried using async and runBlocking but async doesn't work the way I would think it would and runBlocking hangs the entire app
fun backendURL(): String = runBlocking {
var url: String = "localhost"
val job = CoroutineScope(Dispatchers.IO).async {
repo.getTerminalDetails.collect {
it.backendHost
}
}
url
}
Can anyone give me some assistance on getting this to work?
EDIT: Here is my temporary solution, I do not intend on keeping it this way, The issue with runBlocking{} turned out to be the Flow<T> does not finish so runBlocking{} continues to block the app.
fun backendURL(): String {
val details = MutableStateFlow<TerminalDetails>(TerminalDetails.getDefaultInstance())
val job = CoroutineScope(Dispatchers.IO).launch {
repo.getTerminalDetails.collect {
details.value = it
}
}
runBlocking {
delay(250L)
}
return details.value.backendHost
}
EDIT 2: I fully fixed my issue. I created a method with the same name as my val (personal decision) which utilizes runBlocking{} and Flow<T>.first() to block while the value is retrieve. The reason I did not replace my val with the function is there are places where I need the information as well where I can utilize coroutines properly where I am not initializing components on my app
val getTerminalDetails: Flow<TerminalDetails> = cxt.terminalDetails.data
.catch { e ->
if (e is IOException) {
Log.d("Error", e.message.toString())
emit(TerminalDetails.getDefaultInstance())
} else {
throw e
}
}
fun getTerminalDetails(): TerminalDetails = runBlocking {
cxt.terminalDetails.data.first()
}
I'm expecting that the observer will be triggered when I'm hitting API by clicking one of the side menu. When I clicked one of the menu, Retrofit actually gave me the response with the correct value. The problem is, the Observer isn't getting triggered for the second time. I've trace the problem and find out that my Repository isn't returning a value even though my Retrofit already update the MutableLiveData.
RemoteDataSource.kt
override fun getDisastersByFilter(filter: String?): LiveData<ApiResponse<DisastersDTO?>> {
val result = MutableLiveData<ApiResponse<DisastersDTO?>>()
apiService.getDisastersByFilter(filter).enqueue(object : Callback<DisastersResponse> {
override fun onResponse(
call: Call<DisastersResponse>,
response: Response<DisastersResponse>
) {
if(response.isSuccessful) {
val data = response.body()
data?.disastersDTO?.let {
result.postValue(ApiResponse.Success(it))
Log.d("RemoteDataSource", "$it")
} ?: run {
result.postValue(ApiResponse.Error("Bencana alam tidak ditemukan"))
}
} else {
result.postValue(ApiResponse.Error("Terjadi kesalahan!"))
}
}
override fun onFailure(call: Call<DisastersResponse>, t: Throwable) {
result.postValue(ApiResponse.Error(t.localizedMessage!!))
Log.d("RemoteDataSource", t.localizedMessage!!)
}
})
return result
}
Repository.kt
override fun getDisastersByFilter(filter: String?): LiveData<Resource<List<Disaster>>> =
remoteDataSource.getDisastersByFilter(filter).map {
when (it) {
is ApiResponse.Empty -> Resource.Error("Terjadi error")
is ApiResponse.Error -> Resource.Error(it.errorMessage)
is ApiResponse.Loading -> Resource.Loading()
is ApiResponse.Success -> Resource.Success(
DataMapper.disastersResponseToDisasterDomain(
it.data
)
)
}
}
SharedViewModel.kt
fun getDisastersByFilter(filter: String? = "gempa"): LiveData<Resource<List<Disaster>>> =
useCase.getDisastersByFilter(filter)
Here's the **MapsFragment**
private val viewModel: SharedViewModel by activityViewModels()
viewModel.getDisastersByFilter("gempa").observe(viewLifecycleOwner) {
when (it) {
is Resource.Success -> {
Log.d("MapsFragmentFilter", "${it.data}")
it.data?.let { listDisaster ->
if(listDisaster.isNotEmpty()) {
map.clear()
addGeofence(listDisaster)
listDisaster.map { disaster ->
placeMarker(disaster)
addCircle(disaster)
}
}
}
}
is Resource.Error -> Toast.makeText(context, "Filter Error", Toast.LENGTH_SHORT).show()
is Resource.Loading -> {}
}
}
Here's the MainActivity that triggers the function to hit API
private val viewModel: SharedViewModel by viewModels()
binding.navViewMaps.setNavigationItemSelectedListener { menu ->
when (menu.itemId) {
R.id.filter_gempa -> viewModel.getDisastersByFilter("gempa")
R.id.filter_banjir -> viewModel.getDisastersByFilter("banjir")
R.id.about_us -> viewModel.getDisasters()
}
binding.drawerLayoutMain.closeDrawers()
true
}
I can't be sure from what you've posted, but your menu options call getDisastersByFilter on your SharedViewModel, and it looks like that eventually calls through to getDisastersByFilter in RemoteDataSource.
That function creates a new LiveData and returns it, and all your other functions (including the one in viewModel) just return that new LiveData. So if you want to see the result that's eventually posted to it, you need to observe that new one.
I don't know where the fragment code you posted is from, but it looks like you're just calling and observing viewModel.getDisastersByFilter once. So when that first happens, it does the data fetch and you get a result on the LiveData it returned. That LiveData won't receive any more results, from the looks of your code - it's a one-time, disposable thing that receives a result later, and then it's useless.
If I've got that right, you need to rework how you're handling your LiveDatas. The fragment needs to get the result of every viewModel.getDisastersByFilter call, so it can observe the result - it might be better if your activity passes an event to the fragment ("this item was clicked") and the fragment handles calling the VM, and it can observe the result while it's at it (pass it to a function that wires that up so you don't have to keep repeating your observer code)
The other approach would be to have the Fragment observe a currentData livedata, that's wired up to show the value of a different source livedata. Then when you call getDisastersByFilter, that source livedata is swapped for the new one. The currentData one gets any new values posted to this new source, and the fragment only has to observe that single LiveData once. All the data gets piped into it by the VM.
I don't have time to do an example, but have a look at this Transformations stuff (this is one of the developers' blogs): https://medium.com/androiddevelopers/livedata-beyond-the-viewmodel-reactive-patterns-using-transformations-and-mediatorlivedata-fda520ba00b7
What I believe you are doing wrong is using LiveData in the first place while using a retrofit.
You are getting a response asynchronously while your code is running synchronously. So, you need to make use of suspending functions by using suspend.
And while calling this function from ViewModel, wrap it with viewModelScope.launch{}
fun getDisastersByFilter(filter: String? = "gempa") = viewModelScope.launch {
useCase.getDisastersByFilter(filter).collect{
// do something....
// assign the values to MutableLiveData or MutableStateFlows
}
}
You should either be using RxJava or CallbackFlow.
I prefer Flows, given below is an example of how your code might look if you use callback flow.
suspend fun getDisastersByFilter(filter: String?): Flow<ApiResponse<DisastersDTO?>> =
callbackFlow {
apiService.getDisastersByFilter(filter)
.enqueue(object : Callback<DisastersResponse> {
override fun onResponse(
call: Call<DisastersResponse>,
response: Response<DisastersResponse>
) {
if (response.isSuccessful) {
val data = response.body()
data?.disastersDTO?.let {
trySend(ApiResponse.Success(it))
// result.postValue(ApiResponse.Success(it))
Log.d("RemoteDataSource", "$it")
} ?: run {
trySend(ApiResponse.Error("Bencana alam tidak ditemukan"))
// result.postValue(ApiResponse.Error("Bencana alam tidak ditemukan"))
}
} else {
trySend(ApiResponse.Error("Terjadi kesalahan!"))
// result.postValue(ApiResponse.Error("Terjadi kesalahan!"))
}
}
override fun onFailure(call: Call<DisastersResponse>, t: Throwable) {
trySend(ApiResponse.Error(t.localizedMessage!!))
// result.postValue(ApiResponse.Error(t.localizedMessage!!))
Log.d("RemoteDataSource", t.localizedMessage!!)
}
})
awaitClose()
}
using kotlin, having code
fun fetchRemoteDataApi(): Single<RemoteDataResponse> = networkApi.getData()
// it is just a retrofit
#GET(".../api/getData")
fun getData() : Single<RemoteDataResponse>
fun mergeApiWithDb(): Completable = fetchRemoteDataApi()
.zipWith(localDao.getAll())
.flatMapCompletable { (remoteData, localData) ->
doMerge(remoteData, localData) //<== return a Completable
}
the code flow:
val mergeApiDbCall = mergeApiWithDb().onErrorComplete().cache() //<=== would like do some inspection at this level
PublishSubject.create<Unit>().toFlowable(BackpressureStrategy.LATEST)
.compose(Transformers.flowableIO())
.switchMap {
//merge DB with api, or local default value first then listen to DB change
mergeApiDbCall.andThen(listAllTopics())
.concatMapSingle { topics -> remoteTopicUsers.map { topics to it } }
}
.flatMapCompletable { (topics, user) ->
// do something return Completable
}
.subscribe({
...
}, { throwable ->
...
})
and when making the call
val mergeApiDbCall = mergeApiWithDb().onErrorComplete().cache()
the question is if would like to inspect on the Singles<RemoteDataResponse> returned from fetchRemoteDataApi() (i.e. using Log.i(...) to printout the content of RemoteDataResponse, etc.), either in got error or success case, how to do it?
/// the functions
fun listAllTopics(): Flowable<List<String>> = localRepoDao.getAllTopics()
// which a DAO:
#Query("SELECT topic FROM RemoteDataTable WHERE read = 1")
fun getAllTopics(): Flowable<List<String>>
///
private val remoteTopicUsers: Single<List<User>>
get() {
return Single.create {
networkApi.getTopicUsers(object : ICallback.IGetTopicUsersCallback {
override fun onSuccess(result: List<User>) = it.onSuccess(result)
override fun onError(errorCode: Int, errorMsg: String?) = it.onError(Exception(errorCode, errorMsg))
})
}
}
You cannot extract information about elements from the Completable. Though you can use doOnComplete() on Completable, it will not provide you any information about the element.
You can inspect elements if you call doOnSuccess() on your Single, so you need to incorporate this call earlier in your code. To inspect errors you can use doOnError() on both Completable or Single.
I have code that should change SharedPreferences into obsarvable storage with flow so I've code like this
internal val onKeyValueChange: Flow<String> = channelFlow {
val callback = SharedPreferences.OnSharedPreferenceChangeListener { _, key ->
coroutineScope.launch {
//send(key)
offer(key)
}
}
sharedPreferences.registerOnSharedPreferenceChangeListener(callback)
awaitClose {
sharedPreferences.unregisterOnSharedPreferenceChangeListener(callback)
}
}
or this
internal val onKeyValueChange: Flow<String> = callbackFlow {
val callback = SharedPreferences.OnSharedPreferenceChangeListener { _, key ->
coroutineScope.launch {
send(key)
//offer(key)
}
}
sharedPreferences.registerOnSharedPreferenceChangeListener(callback)
awaitClose {
sharedPreferences.unregisterOnSharedPreferenceChangeListener(callback)
}
}
Then I observe this preferences for token, userId, companyId and then log into but there is odd thing as I need to build app three times like changing token not causes tokenFlow to emit anything, then second time new userId not causes userIdFlow to emit anything, then after 3rd login I can logout/login and it works. On logout I am clearing all 3 properties stores in prefs token, userId, companyId.
For callbackFlow:
You cannot use emit() as the simple Flow (because it's a suspend function) inside a callback. Therefore the callbackFlow offers you a synchronized way to do it with the trySend() option.
Example:
fun observeData() = flow {
myAwesomeInterface.addListener{ result ->
emit(result) // NOT ALLOWED
}
}
So, coroutines offer you the option of callbackFlow:
fun observeData() = callbackFlow {
myAwesomeInterface.addListener{ result ->
trySend(result) // ALLOWED
}
awaitClose{ myAwesomeInterface.removeListener() }
}
For channelFlow:
The main difference with it and the basic Flow is described in the documentation:
A channel with the default buffer size is used. Use the buffer
operator on the resulting flow to specify a user-defined value and to
control what happens when data is produced faster than consumed, i.e.
to control the back-pressure behavior.
The trySend() still stands for the same thing. It's just a synchronized way (a non suspending way) for emit() or send()
I suggest you to check Romans Elizarov blog for more detailed information especially this post.
Regarding your code, for callbackFlow you wont' be needing a coroutine launch:
coroutineScope.launch {
send(key)
//trySend(key)
}
Just use trySend()
Another Example, maybe much concrete:
private fun test() {
lifecycleScope.launch {
someFlow().collectLatest {
Log.d("TAG", "Finally we received the result: $it")
// Cancel this listener, so it will not be subscribed anymore to the callbackFlow. awaitClose() will be triggered.
// cancel()
}
}
}
/**
* Define a callbackFlow.
*/
private fun someFlow() = callbackFlow {
// A dummy class which will run some business logic and which will sent result back to listeners through ApiCallback methods.
val service = ServiceTest() // a REST API class for example
// A simple callback interface which will be called from ServiceTest
val callback = object : ApiCallback {
override fun someApiMethod(data: String) {
// Sending method used by callbackFlow. Into a Flow we have emit(...) or for a ChannelFlow we have send(...)
trySend(data)
}
override fun anotherApiMethod(data: String) {
// Sending method used by callbackFlow. Into a Flow we have emit(...) or for a ChannelFlow we have send(...)
trySend(data)
}
}
// Register the ApiCallback for later usage by ServiceTest
service.register(callback)
// Dummy sample usage of callback flow.
service.execute(1)
service.execute(2)
service.execute(3)
service.execute(4)
// When a listener subscribed through .collectLatest {} is calling cancel() the awaitClose will get executed.
awaitClose {
service.unregister()
}
}
interface ApiCallback {
fun someApiMethod(data: String)
fun anotherApiMethod(data: String)
}
class ServiceTest {
private var callback: ApiCallback? = null
fun unregister() {
callback = null
Log.d("TAG", "Unregister the callback in the service class")
}
fun register(callback: ApiCallback) {
Log.d("TAG", "Register the callback in the service class")
this.callback = callback
}
fun execute(value: Int) {
CoroutineScope(Dispatchers.IO).launch {
if (value < 2) {
callback?.someApiMethod("message sent through someApiMethod: $value.")
} else {
callback?.anotherApiMethod("message sent through anotherApiMethod: $value.")
}
}
}
}
I wanted to know how can I send/emit items to a Kotlin.Flow, so my use case is:
In the consumer/ViewModel/Presenter I can subscribe with the collect function:
fun observe() {
coroutineScope.launch {
// 1. Send event
reopsitory.observe().collect {
println(it)
}
}
}
But the issue is in the Repository side, with RxJava we could use a Behaviorsubject expose it as an Observable/Flowable and emit new items like this:
behaviourSubject.onNext(true)
But whenever I build a new flow:
flow {
}
I can only collect. How can I send values to a flow?
If you want to get the latest value on subscription/collection you should use a ConflatedBroadcastChannel:
private val channel = ConflatedBroadcastChannel<Boolean>()
This will replicate BehaviourSubject, to expose the channel as a Flow:
// Repository
fun observe() {
return channel.asFlow()
}
Now to send an event/value to that exposed Flow simple send to this channel.
// Repository
fun someLogicalOp() {
channel.send(false) // This gets sent to the ViewModel/Presenter and printed.
}
Console:
false
If you wish to only receive values after you start collecting you should use a BroadcastChannel instead.
To make it clear:
Behaves as an Rx's PublishedSubject
private val channel = BroadcastChannel<Boolean>(1)
fun broadcastChannelTest() {
// 1. Send event
channel.send(true)
// 2. Start collecting
channel
.asFlow()
.collect {
println(it)
}
// 3. Send another event
channel.send(false)
}
false
Only false gets printed as the first event was sent before collect { }.
Behaves as an Rx's BehaviourSubject
private val confChannel = ConflatedBroadcastChannel<Boolean>()
fun conflatedBroadcastChannelTest() {
// 1. Send event
confChannel.send(true)
// 2. Start collecting
confChannel
.asFlow()
.collect {
println(it)
}
// 3. Send another event
confChannel.send(false)
}
true
false
Both events are printed, you always get the latest value (if present).
Also, want to mention Kotlin's team development on DataFlow (name pending):
https://github.com/Kotlin/kotlinx.coroutines/pull/1354
Which seems better suited to this use case (as it will be a cold stream).
Take a look at MutableStateFlow documentation as it is a replacement for ConflatedBroadcastChannel that is going to be deprecated, very soon.
For a better context, look at the whole discussion on the original issue on Kotlin's repository on Github.
UPDATE:
Kotlin Coroutines 1.4.0 is now available with MutableSharedFlow, which replaces the need for Channel. MutableSharedFlow cleanup is also built in so you don't need to manually OPEN & CLOSE it, unlike Channel. Please use MutableSharedFlow if you need a Subject-like api for Flow
ORIGINAL ANSWER
Since your question had the android tag I'll add an Android implementation that allows you to easily create a BehaviorSubject or a PublishSubject that handles its own lifecycle.
This is relevant in Android because you don't want to forget to close the channel and leak memory. This implementation avoids the need to explicitly "dispose" of the reactive stream by tying it to the creation and destruction of the Fragment/Activity. Similar to LiveData
interface EventReceiver<Message> {
val eventFlow: Flow<Message>
}
interface EventSender<Message> {
fun postEvent(message: Message)
val initialMessage: Message?
}
class LifecycleEventSender<Message>(
lifecycle: Lifecycle,
private val coroutineScope: CoroutineScope,
private val channel: BroadcastChannel<Message>,
override val initialMessage: Message?
) : EventSender<Message>, LifecycleObserver {
init {
lifecycle.addObserver(this)
}
override fun postEvent(message: Message) {
if (!channel.isClosedForSend) {
coroutineScope.launch { channel.send(message) }
} else {
Log.e("LifecycleEventSender","Channel is closed. Cannot send message: $message")
}
}
#OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
fun create() {
channel.openSubscription()
initialMessage?.let { postEvent(it) }
}
#OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
fun destroy() {
channel.close()
}
}
class ChannelEventReceiver<Message>(channel: BroadcastChannel<Message>) :
EventReceiver<Message> {
override val eventFlow: Flow<Message> = channel.asFlow()
}
abstract class EventRelay<Message>(
lifecycle: Lifecycle,
coroutineScope: CoroutineScope,
channel: BroadcastChannel<Message>,
initialMessage: Message? = null
) : EventReceiver<Message> by ChannelEventReceiver<Message>(channel),
EventSender<Message> by LifecycleEventSender<Message>(
lifecycle,
coroutineScope,
channel,
initialMessage
)
By using the Lifecycle library from Android, I can now create a BehaviorSubject that cleans itself up after the activity/fragment has been destroyed
class BehaviorSubject<String>(
lifecycle: Lifecycle,
coroutineScope: CoroutineScope,
initialMessage = "Initial Message"
) : EventRelay<String>(
lifecycle,
coroutineScope,
ConflatedBroadcastChannel(),
initialMessage
)
or I can create a PublishSubject by using a buffered BroadcastChannel
class PublishSubject<String>(
lifecycle: Lifecycle,
coroutineScope: CoroutineScope,
initialMessage = "Initial Message"
) : EventRelay<String>(
lifecycle,
coroutineScope,
BroadcastChannel(Channel.BUFFERED),
initialMessage
)
And now I can do something like this
class MyActivity: Activity() {
val behaviorSubject = BehaviorSubject(
this#MyActivity.lifecycle,
this#MyActivity.lifecycleScope
)
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
if (savedInstanceState == null) {
behaviorSubject.eventFlow
.onEach { stringEvent ->
Log.d("BehaviorSubjectFlow", stringEvent)
// "BehaviorSubjectFlow: Initial Message"
// "BehaviorSubjectFlow: Next Message"
}
.flowOn(Dispatchers.Main)
.launchIn(this#MyActivity.lifecycleScope)
}
}
override fun onResume() {
super.onResume()
behaviorSubject.postEvent("Next Message")
}
}