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.
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 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.
I am trying to implement android MVI architecture using state flow and paging 3 but I got confused when I had a view state which contains paging data.
The problem is that I expose the view state from view model as a state flow object, but now inside that view state I have another flow object which comes from the paging library.
Is it OK to have a flow inside a state flow? and if it’s not what should I do instead?
This is my code for more clarification.
TaskRepository
override fun list(
pageNumber: Int,
pageSize: Int,
groupId: Long?,
query: String
): Flow<PagingData<Task>> {
return Pager(
config = PagingConfig(
pageSize = Consts.PageSize,
maxSize = 200,
enablePlaceholders = false
),
remoteMediator = TaskRemoteMediator(query, groupId, db, taskApi),
pagingSourceFactory = {
TaskDataSource(taskApi, groupId, query)
}
).flow
}
TaskViewModel
viewModelScope.launch {
try {
_taskListViewState.emit(TaskListViewState.Loading)
val tasks = taskRepo.list(1, Consts.PageSize, intent.groupId, "")
_taskListViewState.emit(TaskListViewState.Data(tasks))
} catch (e: Exception) {
_taskListViewState.emit(TaskListViewState.Error(R.string.unknown_error))
}
}
TaskListViewState
sealed class TaskListViewState {
object Idle : TaskListViewState()
object Loading : TaskListViewState()
data class Data(val tasks: Flow<PagingData<Task>>) : TaskListViewState()
data class Error(val error: Int) : TaskListViewState()
}
TaskListFragment
private fun observeViewState() {
lifecycleScope.launchWhenStarted {
viewModel.taskListViewState.collect {
render(it)
}
}
}
private fun render(viewState: TaskListViewState) {
Log.d(TAG, "render: $viewState")
when (viewState) {
is TaskListViewState.Loading -> showLoading()
is TaskListViewState.Idle -> hildeLoading()
is TaskListViewState.Error -> {
hildeLoading()
showMessage(viewState.error)
}
is TaskListViewState.Data -> {
hildeLoading()
lifecycleScope.launchWhenCreated {
viewState.tasks.collectLatest {
tasksAdapter.submitData(lifecycle, it)
}
}
}
}
}
A bit late but you can modify the classes like below and you wouldn't need flow inside the TaskListViewState.
TaskListViewState
sealed class TaskListViewState {
object Idle : TaskListViewState()
object Loading : TaskListViewState()
data class Data(val tasks: PagingData<Task>) : TaskListViewState()
data class Error(val error: Int) : TaskListViewState()
}
TaskViewModel
viewModelScope.launch {
try {
_taskListViewState.emit(TaskListViewState.Loading)
taskRepo.list(1, Consts.PageSize, intent.groupId, "")
.cacheIn(viewModelScope)
.collectLatest { pagingData ->
_taskListViewState.emit(TaskListViewState.Data(pagingData))
}
} catch (e: Exception) {
_taskListViewState.emit(TaskListViewState.Error(R.string.unknown_error))
}
}
TaskListFragment
private fun observeViewState() {
lifecycleScope.launchWhenStarted {
viewModel.taskListViewState.collect {
render(it)
}
}
}
private fun render(viewState: TaskListViewState) {
Log.d(TAG, "render: $viewState")
when (viewState) {
is TaskListViewState.Loading -> showLoading()
is TaskListViewState.Idle -> hildeLoading()
is TaskListViewState.Error -> {
hildeLoading()
showMessage(viewState.error)
}
is TaskListViewState.Data -> {
hildeLoading()
tasksAdapter.submitData(lifecycle, viewState.tasks)
}
}
}
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()
}
I am working on creating my MVVM template project.
The way MVVM work's is that the View observes changes to the VM and reacts to them. How would i implement that logic in the following example.
View code:
fun addPost(): Unit {
viewModel.addPost(dataSource.text.get(), dataSource.title.get(), { postID: Long ->
if (postID.equals(0)) {
Toast.makeText(MyApp.instance.getContext(), "Error", Toast.LENGTH_LONG).show()
} else {
(arguments.get(ARG_RunOnPositiveDismiss) as (DMPost) -> Unit)(DMPost(postID, MyOptions.User.GET()!!.UserID, dataSource.title.get(), dataSource.text.get()))
dismiss()
}
})
}
ViewModel code:
fun addPost(title:String,text:String,onSuccess: (Long) -> Unit): Unit {
rep.insertPost(DMPost(0, MyOptions.User.GET()!!.UserID, title, text),onSuccess)
}
Repository code:
fun insertPost(post: DMPost, onSuccess: (Long) -> Unit) {
if (MyOptions.Online.GET()!!) {
val client = retrofit.create(APIPost::class.java)
val insertPost: Call<Long> = client.insertPost(post)
insertPost.enqueue(object : Callback<Long> {
override fun onResponse(call: Call<Long>, response: Response<Long>) {
if (response.isSuccessful) {
onSuccess(response.body()!!)
} else {
onSuccess(0)
}
}
override fun onFailure(call: Call<Long>, t: Throwable) {
onSuccess(0)
}
})
} else {
AsyncTask.execute {
try {
onSuccess(daoPost.insertPost(EntityPost(post)))
} catch (e: Exception) {
onSuccess(0)
}
}
}
}
I am assuming that i need to have 2 methods in my view, one for showing the error toast and the other for success.the view should observe a value on the VM and on a change on that value, should call one of those 2 methods.
Is my assumption right?
If yes, can someone write the code for that logic?
In your viewmodel:
private MediatorLiveData<YourDataType> mDataObserved;
public LiveData<YourDataType> getDataObserved(){
return mDataObserved;
}
And in your view:
viewModel.getDataObserved().observer(this, Observer<YourDataType>{
// do update view logic in here
});
Last, in your repository callback call viewmodel to notify data changed:
mDataObserved.postValue(YourDataValue);