I have a RecyclerView that inherits from PagingDataAdapter, inside the adapter I have two viewHolders, they are divided by viewType, the fact is that I wrote a code that combined the body of two requests into one MutableLiveData, which can then be observed in a fragment and set its value via submitData.
private val _searchResult = MutableLiveData<Resource<PagingData<SearchItems>>>()
val searchResult: LiveData<Resource<PagingData<SearchItems>>> = _searchResult
fun getSearchResult(q: String, id: String) = viewModelScope.launch {
_searchResult.postValue(Resource.Loading())
val searchDeferred = async { repository.getSearch(q) }
val channelsDeferred = async { repository.fetchChannels(id) }
val search = searchDeferred.await()
val channels = channelsDeferred.await()
channels.collect {
_searchResult.value = Resource.Success(it)
}
search.collect {
_searchResult.value = Resource.Success(it)
}
}
this is the code in the ViewModel
viewModel.searchResult.observe(viewLifecycleOwner, {
when (it) {
is Resource.Error -> {
it.message?.let { it1 -> Log.d("mecal", it1) }
}
is Resource.Success -> {
lifecycleScope.launch {
it.data?.map { item ->
viewModel.getSearchResult(
args.query,
item.snippet?.channelId.toString()
)
}
it.data?.let { it1 -> searchAdapter.submitData(it1) }
}
}
}
})
and is the code in the Fragment. The point is that this code does not work, i.e. it does not display data in the recyclerview. But I don’t know what exactly I did wrong, if you have any suggestions why it doesn’t work or there is another way, please write, I really need it!
Here I have something very similar that you need. It is a chat app that uses the same RecyclerView to display 2 different viewholders depending on if the message is sent to you or you sent the message
Related
I have the following setup.
I have a screen with a list of items (PlantsScreen). When clicking on an item from the list I will be navigated to another screen (AddEditPlantScreen). After editing and saving the item and navigating back to the listScreen, I want to show the updated list of items. But the list is not displaying the updated list but the list before the edit of the item.
In order to have a single source of truth, I am fetching the data from a node.js Back-End and then saving it to the local repository (Room). I think I need to refresh the state in the ViewModel to fetch the updated list from my repository.
I know I can use a Job to do this, but it throws me an error. Is this the correct approach when returning a Flow?
If yes, how can I achieve this.
If not, what alternative approach do I have?
plantsListViewModel.kt
private val _state = mutableStateOf<PlantsState>(PlantsState())
val state: State<PlantsState> = _state
init {
getPlants(true, "")
}
private fun getPlants(fetchFromBackend: Boolean, query: String) {
viewModelScope.launch {
plantRepository.getPlants(fetchFromBackend, query)
.collect { result ->
when (result) {
is Resource.Success -> {
result.data?.let { plants ->
_state.value = state.value.copy(
plants = plants,
)
}
}
}
}
}
}
Here is my repository where I fetch the items in the list from.
// plantsRepository.kt
override suspend fun getPlants(
fetchFromBackend: Boolean,
query: String
): Flow<Resource<List<Plant>>> {
return flow {
emit(Resource.Loading(true))
val localPlants = dao.searchPlants(query)
emit(
Resource.Success(
data = localPlants.map { it.toPlant() },
)
)
val isDbEmpty = localPlants.isEmpty() && query.isBlank()
val shouldLoadFromCache = !isDbEmpty && !fetchFromBackend
if (shouldLoadFromCache) {
emit(Resource.Loading(false))
return#flow
}
val response = plantApi.getPlants().plants
dao.clearPlants()
dao.insertPlants(
response.map { it.toPlantEntity() }
)
emit(Resource.Success(
data = dao.searchPlants("").map { it.toPlant() }
))
emit(Resource.Loading(false))
}
}
The full code for reference can be found here:
https://gitlab.com/fiehra/plants
Thank you!
You actually have two sources of truth: One is the room database, the other the _state object in the view model.
To reduce this to a single source of truth you need to move the collection of the flow to the compose function where the data is needed. You will do this using the extension function StateFlow.collectAsStateWithLifecycle() from the artifact androidx.lifecycle:lifecycle-runtime-compose. This will automatically subscribe and unsubscribe the flow when your composable enters and leaves the composition.
Since you want the business logic to stay in the view model you have to apply it before the flow is collected. The idea is to only transform the flow in the view model:
class PlantsViewModel {
private var fetchFromBackend: Boolean by mutableStateOf(true)
private var query: String by mutableStateOf("")
#OptIn(ExperimentalCoroutinesApi::class)
val state: StateFlow<PlantsState> =
snapshotFlow { fetchFromBackend to query }
.flatMapLatest { plantRepository.getPlants(it.first, it.second) }
.mapLatest(PlantsState::of)
.stateIn(
scope = viewModelScope,
started = SharingStarted.WhileSubscribed(5_000),
initialValue = PlantsState.Loading,
)
// ...
}
If you want other values for fetchFromBackend and query you just need to update the variables; the flow will automatically recalculate the state object. It can be as simple as just calling something like this:
fun requestPlant(fetchFromBackend: Boolean, query: String) {
this.fetchFromBackend = fetchFromBackend
this.query = query
}
The logic to create a PlantsState from a result can then be done somewhere else in the view model. Replace your PlantsViewModel.getPlants() with this and place it at file level outside of the PlantsViewModel class:
private fun PlantsState.Companion.of(result: Resource<List<Plant>>): PlantsState = when (result) {
is Resource.Success -> {
result.data?.let { plants ->
PlantsState.Success(
plants = plants,
)
} ?: TODO("handle case where result.data is null")
}
is Resource.Error -> {
PlantsState.Error("an error occurred")
}
is Resource.Loading -> {
PlantsState.Loading
}
}
With the PlantsState class replaced by this:
sealed interface PlantsState {
object Loading : PlantsState
data class Success(
val plants: List<Plant> = emptyList(),
val plantOrder: PlantOrder = PlantOrder.Name(OrderType.Descending),
val isOrderSectionVisible: Boolean = false,
) : PlantsState
data class Error(
val error: String,
) : PlantsState
companion object
}
Then, wherever you need the state (in PlantsScreen f.e.), you can get a state object with
val state by viewModel.state.collectAsStateWithLifecycle()
Thanks to kotlin flows state will always contain the most current data from the room database, and thanks to the compose magic your composables will always update when anything in the state object updates, so that you really only have one single source of truth.
Additionally:
PlantRepository.getPlants() should not be marked as a suspend function because it just creates a flow and won't block; long running data retrieval will be done in the collector.
You will need to manually import androidx.compose.runtime.getValue and the androidx.compose.runtime.setValue for some of the delegates to work.
After #Leviathan was able to point me in the right direction i refactored my code by changing the return types of my repository functions, implementing use cases and returning a Flow<List<Plant>> instead of Flow<Resource<List<Plant>>> for simplicity purposes.
Further removed the suspend marker of the functions in the PlantDao.kt and PlantRepository.kt as pointed out by Leviathan.
// PlantRepositoryImplementation.kt
override fun getPlants(
fetchFromBackend: Boolean,
query: String
): Flow<List<Plant>> {
return flow {
if (fetchFromBackend) {
val response = plantApi.getPlants().plants
dao.clearPlants()
dao.insertPlants(
response.map { it.toPlantEntity() }
)
val localPlants = dao.searchPlants(query)
localPlants.collect { plants ->
emit(plants.map { it.toPlant() })
return#collect
}
} else {
val localPlants = dao.searchPlants(query)
localPlants.collect { plants ->
emit(plants.map { it.toPlant() })
return#collect
}
}
}
}
I started using a Job and GetPlants usecase in my viewModel like this:
// PlantsViewModel.kt
private fun getPlants(plantOrder: PlantOrder, fetchFromBackend: Boolean, query: String) {
getPlantsJob?.cancel()
getPlantsJob = plantUseCases.getPlants(plantOrder, fetchFromBackend, query)
.onEach { plants ->
_state.value = state.value.copy(
plants = plants,
plantOrder = plantOrder
)
}.launchIn(viewModelScope)
I also had to remove the suspend in the PlantDao.kt
// PlantDao.kt
fun searchPlants(query: String): Flow<List<PlantEntity>>
This is the code for my GetPlants usecase:
// GetPlantsUsecase.kt
class GetPlants
(
private val repository: PlantRepository,
) {
operator fun invoke(
plantOrder: PlantOrder = PlantOrder.Name(OrderType.Descending),
fetchFromBackend: Boolean,
query: String
): Flow<List<Plant>> {
return repository.getPlants(fetchFromBackend, query).map { plants ->
when (plantOrder.orderType) {
is OrderType.Ascending -> {
// logic for sorting
}
}
is OrderType.Descending -> {
// logic for sorting
}
}
}
}
}
Need to collect flow in ViewModel and after some data modification, the UI is updated using _batteryProfileState.
Inside compose I'm collecting states like this
val batteryProfile by viewModel.batteryProfileState.collectAsStateWithLifecycle()
batteryProfile.voltage
In ViewModel:
private val _batteryProfileState = MutableStateFlow(BatteryProfileState())
val batteryProfileState = _batteryProfileState.asStateFlow()
private fun getBatteryProfileData() {
viewModelScope.launch {
// FIXME In viewModel we should not collect it like this
_batteryProfile(Unit).collect { result ->
_batteryProfileState.update { state ->
when(result) {
is Result.Success -> {
state.copy(
voltage = result.data.voltage?.toString()
?.plus(result.data.voltageUnit
)
}
is Result.Error -> {
state.copy(
errorMessage = _context.getString(R.string.something_went_wrong)
)
}
}
}
}
}
}
The problem is when I put my app in the background the _batteryProfile(Unit).collect does not stop collecting while in UI batteryProfile.voltage stop updating UI which is correct behavior as I have used collectAsStateWithLifecycle() for UI.
But I have no idea how to achieve the same behavior for ViewModel.
In ViewModel I have used stateIn operator and access data like below everything working fine now:
val batteryProfileState = _batteryProfile(Unit).map { result ->
when(result) {
is Result.Success -> {
BatteryProfileState(
voltage = result.data.voltage?.toString()
?.plus(result.data.voltageUnit.unit)
?: _context.getString(R.string.msg_unknown),
)
}
is Result.Error -> {
BatteryProfileState(
errorMessage = _context.getString(R.string.something_went_wrong)
)
}
}
}.stateIn(viewModelScope, WhileViewSubscribed, BatteryProfileState())
collecting data in composing will be the same
Explanation: WhileViewSubscribed Stops updating data while the app is in the background for more than 5 seconds.
val WhileViewSubscribed = SharingStarted.WhileSubscribed(5000)
You can try to define getBatteryProfileData() as suspend fun:
suspend fun getBatteryProfileData() {
// FIXME In viewModel we should not collect it like this
_batteryProfile(Unit).collect { result ->
_batteryProfileState.update { state ->
when(result) {
is Result.Success -> {
state.copy(
voltage = result.data.voltage?.toString()
?.plus(result.data.voltageUnit
)
}
is Result.Error -> {
state.copy(
errorMessage = _context.getString(R.string.something_went_wrong)
)
}
}
}
}
}
And than in your composable define scope:
scope = rememberCoroutineScope()
scope.launch {
yourviewmodel.getBatteryProfileData()
}
And I think you can move suspend fun getBatteryProfileData() out of ViewModel class...
Hey I am working in Android Kotlin. I am learning this LatestNewsUiState sealed class example from Android doc. I made my own sealed class example. But I am confused little bit, how can I achieved this. Is I am doing right for my scenario or not?
DataState.kt
sealed class DataState {
data class DataFetch(val data: List<Xyz>?) : DataState()
object EmptyOnFetch : DataState()
object ErrorOnFetch : DataState()
}
viewmodel.kt
var dataMutableStateFlow = MutableStateFlow<DataState>(DataState.EmptyOnFetch)
fun fetchData() {
viewModelScope.launch {
val result = repository.getData()
result.handleResult(
onSuccess = { response ->
if (response?.items.isNullOrEmpty()) {
dataMutableStateFlow.value = DataState.EmptyOnFetch
} else {
dataMutableStateFlow.value = DataState.DataFetch(response?.items)
}
},
onError = {
dataMutableStateFlow.value = DataState.ErrorOnFetch
}
)
}
}
fun fetchMoreData() {
viewModelScope.launch {
val result = repository.getData()
result.handleResult(
onSuccess = { response ->
if (response?.items.isNullOrEmpty()) {
dataMutableStateFlow.value = DataState.EmptyOnFetch
} else {
dataMutableStateFlow.value = DataState.DataFetch(response?.items)
}
},
onError = {
dataMutableStateFlow.value = DataState.ErrorOnFetch
}
)
}
}
Activity.kt
lifecycleScope.launchWhenStarted {
viewModel.dataMutableStateFlow.collectLatest { state ->
when (state) {
is DataState.DataFetch -> {
binding.group.visibility = View.VISIBLE
}
DataState.EmptyOnFetch,
DataState.ErrorOnFetch -> {
binding.group.visibility = View.GONE
}
}
}
}
}
I have some points which I want to achieve in the standard ways.
1. When your first initial api call fetchData() if data is not null or empty then we need to show view. If data is empty or null then we need to hide the view. But if api fail then we need to show an error message.
2. When view is visible and view is showing some data. Then we call another api fetchMoreData() and data is empty or null then I don't want to hide view as per code is written above. And If api fails then we show error message.
Thanks in advance
Situation
I submit data setTripDeliver, the collect works fine (trigger LOADING and then SUCCESS). I pressed a button go to next fragment B (using replace). After that, I press back button (using popbackstack). the collect SUCCESS triggered.
Codes Related
These codes at the FragmentA.kt inside onViewCreated.
private fun startLifeCycle() {
viewLifecycleOwner.lifecycleScope.launch {
viewLifecycleOwner.lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
launch {
collectTripDeliver()
}
launch {
collectTripReattempt()
}
}
}
}
These codes when to submit data at a button setOnClickListener.
viewLifecycleOwner.lifecycleScope.launchWhenStarted {
viewModel.setTripDeliver(
verificationCode,
remark
)
}
Method to collect flow collectTripReattempt()
private suspend fun collectTripReattempt() {
viewModel.tripReattempt.collect {
when (it) {
is Resource.Initialize -> {
}
is Resource.Loading -> {
Log.i("???","collectTripReattempt loading")
handleSaveEarly()
}
is Resource.Success -> {
val error = it.data?.error
if (error == null) {
Tools.showToast(requireContext(), "Success Reattempt")
Log.i("???","collectTripReattempt Success")
} else {
Tools.showToast(requireContext(), "$error")
}
handleSaveEnding()
}
is Resource.Error -> {
handleSaveEnding()
}
}
}
}
Below codes are from ViewModel.
private val _tripDeliver =
MutableStateFlow<Resource<TripDeliverResponse>>(Resource.Initialize())
val tripDeliver: StateFlow<Resource<TripDeliverResponse>> = _tripDeliver
This method to call repository.
suspend fun setTripDeliver(
verificationCode: String?,
remark: String?
) {
_tripDeliver.value = Resource.Loading()
try {
val result = withContext(ioDispatcher) {
val tripDeliverParameter = DeliverParameter(
verificationCode,
remark
)
val response = appRepository.setTripDeliver(tripDeliverParameter)
Resource.getResponse { response }
}
_tripDeliver.value = result
} catch (e: Exception) {
when (e) {
is IOException -> _tripDeliver.value =
Resource.Error(messageInt = R.string.no_internet_connection)
else -> _tripDeliver.value =
Resource.Error("Trip Deliver Error: " + e.message)
}
}
}
Logcat
2021-07-09 19:56:10.946 7446-7446/com.package.app I/???: collectTripReattempt loading
2021-07-09 19:56:11.172 7446-7446/com.package.app I/???: collectTripReattempt Success
2021-07-09 19:56:17.703 7446-7446/com.package.app I/???: collectTripReattempt Success
As you can see, the last Success is called again AFTER I pressed back button (popbackstack)
Question
How to make it trigger once only? Is it the way I implement it is wrong? Thank you in advance.
This is not problem of your implementation this is happening because of stateIn() which use used in your viewModel to convert regular flow into stateFlow
If according to your code snippet the success is triggered once again, then why not loading has triggered?
as per article, it is showing the latest cached value when you left the screen and came back you got the latest cached value on view.
Resource:
https://medium.com/androiddevelopers/migrating-from-livedata-to-kotlins-flow-379292f419fb
The latest value will still be cached so that when the user comes back to it, the view will have some data immediately.
I have found the solution, thanks to #Nurseyit Tursunkulov for giving me a clue. I have to use SharedFlow.
At the ViewModel, I replace the initialize with these:
private val _tripDeliver = MutableSharedFlow<Resource<TripDeliverResponse>>(replay = 0)
val tripDeliver: SharedFlow<Resource<TripDeliverResponse>> = _tripDeliver
At the replay I have to use 0, so this SharedFlow will trigger once. Next, change _tripDeliver.value to _tripDeliver.emit() like the codes below:
fun setTripDeliver(
verificationCode: String?,
remark: String?
) = viewModelScope.launch {
_tripDeliver.emit(Resource.Loading())
if (verificationCode == null && remark == null) {
_tripDeliver.emit(Resource.Error("Remark cannot be empty if verification is empty"))
return#launch
}
try {
val result = withContext(ioDispatcher) {
val tripDeliverParameter = DeliverParameter(
verificationCode,
remark,
)
val response = appRepository.setTripDeliver(tripDeliverParameter)
Resource.getResponse { response }
}
_tripDeliver.emit(result)
} catch (e: Exception) {
when (e) {
is IOException -> _tripDeliver.emit(Resource.Error(messageInt = R.string.no_internet_connection))
else -> _tripDeliver.emit(Resource.Error("Trip Deliver Error: " + e.message))
}
}
}
I hope this answer will help the others also.
I think this is because of coldFlow, you need a HotFlow. Another option is to try to hide and show fragment, instead of replacing. And yet another solution is to keep this code in viewModel.
In my opinion, I think your way of using coroutines in lifeScope is incorrect. After the lifeScope status of FragmentA is at Started again, the coroutine will be restarted:
launch {
collectTripDeliver()
}
launch {
collectTripReattempt()
}
So I think: You need to modify this way:
private fun startLifeCycle() {
viewLifecycleOwner.lifecycleScope.launch {
launch {
collectTripDeliver()
}
launch {
collectTripReattempt()
}
}
}
In my app, I have this flow:
ClickListender in my fragment:
search_button.setOnClickListener {
if(search_input.text.isNullOrEmpty())
Toast.makeText(activity, "Input Error", Toast.LENGTH_LONG).show()
else
viewModel.onSearchButtonClicked(search_input.text.toString())
}
onSearchButtonClicked inside viewModel:
fun onSearchButtonClicked(input: String) {
coroutineScope.launch {
repo.insertToDatabase(input)
}
}
insertToDatabase inside Repository:
suspend fun insertToDatabase(string: String) {
withContext(Dispatchers.IO) {
val dataList =
ExternalApi.retrofitCall.getData(string).await()
if (dataList.intialDataResult < 1) {
//show error
} else {
//all good
database.myDataBase.insertAll(dataList)
}
}
}
I need to show error message if intialDataResult is less then one.
I thought about create MutableLiveData inside my repository with initial value of false and listen from the fragment through the viewModel, but it's not good approach because I have no way to set the LiveData to "false" again after I show error message.
I also tried to return bool from the insertToDatabase function and decide if to show error or not, with no success.
Any ideas how can I solve this?
Why not create a LiveData to manage your work's result state?
Create a class to store result of work why sealed class?
sealed class ResultState{
object Success: ResultState() // this is object because I added no params
data class Failure(val message: String): ResultState()
}
Create a LiveData to report this result
val stateLiveData = MutableLiveData<ResultState>()
Make insertToDatabase() return a result
suspend fun insertToDatabase(input: String): ResultState {
return withContext<ResultState>(Dispatchers.IO) {
val dataList =
ExternalApi.retrofitCall.getData(string).await()
if (dataList.intialDataResult < 1) {
return#withContext ResultState.Failure("Reason of error...")
} else {
database.myDataBase.insertAll(dataList)
return#withContext ResultState.Success
}
}
}
Now, report result to UI
fun onSearchButtonClicked(input: String) {
coroutineScope.launch {
val resultState = repo.insertToDatabase(input)
stateLiveData.value = resultState
}
}
In UI,
viewModel.stateLiveData.observe(viewLifeCycleOwner, Observer { state ->
when (state) {
is ResultState.Success -> { /* show success in UI */ }
is ResultState.Failure -> { /* show error in UI with state.message variable */ }
}
})
Similarly, you can add a ResultState.PROGRESS to show that a task is running in the UI.
If you have any queries, please add a comment.