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Combining Two Flows and add them to temporary list of StateFlow(Hot Flows)

I m getting data from two End points using flows and assigning those two list to temporary list in ViewModel. For this purpose, I'm using combine function and returning result as stateFlows with stateIn operator but that's not working. Can anyone point me out where I go wrong please.
ViewModel.kt
private val _movieItem: MutableStateFlow<State<List<HomeRecyclerViewItems>>> =
MutableStateFlow(State.Loading())
val movieItems: StateFlow<State<List<HomeRecyclerViewItems>>> = _movieItem
fun getHomeItemList() {
viewModelScope.launch {
val testList: Flow<State<List<HomeRecyclerViewItems.Movie>>> =
settingsRepo.getMovieList().map {
State.fromResource(it)
}
val directorList: Flow<State<List<HomeRecyclerViewItems.Directors>>> =
settingsRepo.getDirectorList().map {
State.fromResource(it)
}
_movieItem.value = combine(testList, directorList) { testList, directorList ->
testList + directorList // This is not working as "+" Unresolve Error
}.stateIn(
viewModelScope,
SharingStarted.WhileSubscribed(5000),
State.loading<Nothing>()
) as State<List<HomeRecyclerViewItems>> // Unchecked cast: StateFlow<Any> to State<List<HomeRecyclerViewItems>>
}
Repository.kt
fun getMovieList(): Flow<ResponseAPI<List<HomeRecyclerViewItems.Movie>>> {
return object :
NetworkBoundRepository<List<HomeRecyclerViewItems.Movie>, List<HomeRecyclerViewItems.Movie>>() {
override suspend fun saveRemoteData(response: List<HomeRecyclerViewItems.Movie>) {
}
override fun fetchFromLocal() {
}
override suspend fun fetchFromRemote(): Response<List<HomeRecyclerViewItems.Movie>> =
apiInterface.getMoviesList()
}.asFlow()
}
fun getDirectorList(): Flow<ResponseAPI<List<HomeRecyclerViewItems.Directors>>> {
return object :
NetworkBoundRepository<List<HomeRecyclerViewItems.Directors>, List<HomeRecyclerViewItems.Directors>>() {
override suspend fun saveRemoteData(response: List<HomeRecyclerViewItems.Directors>) {
}
override fun fetchFromLocal() {
}
override suspend fun fetchFromRemote(): Response<List<HomeRecyclerViewItems.Directors>> =
apiInterface.getDirectorsList()
}.asFlow()
}
Network BoundRepository.kt
#ExperimentalCoroutinesApi
abstract class NetworkBoundRepository<RESULT, REQUEST> {
fun asFlow() = flow<ResponseAPI<REQUEST>> {
val apiResponse = fetchFromRemote()
val remotePosts = apiResponse.body()
if (apiResponse.isSuccessful && remotePosts != null) {
emit(ResponseAPI.Success(remotePosts))
} else {
emit(ResponseAPI.Failed(apiResponse.errorBody()!!.string()))
}
}.catch { e ->
e.printStackTrace()
emit(ResponseAPI.Failed("Server Problem! Please try again Later. "))
}
#WorkerThread
protected abstract suspend fun saveRemoteData(response: REQUEST)
#MainThread
protected abstract fun fetchFromLocal()
#MainThread
protected abstract suspend fun fetchFromRemote(): Response<REQUEST>
}
Endpoints with Sealed Class
#GET("directors")
fun getDirectorsList(): Response<List<HomeRecyclerViewItems.Directors>>
#GET("movies")
fun getMoviesList(): Response<List<HomeRecyclerViewItems.Movie>>
sealed class HomeRecyclerViewItems {
class Title(
val id: Int,
val title: String
) : HomeRecyclerViewItems()
class Movie(
val id: Int,
val title: String,
val thumbnail: String,
val releaseDate: String
) : HomeRecyclerViewItems()
class Directors(
val id: Int,
val name: String,
val avator: String,
val movie_count: Int
) : HomeRecyclerViewItems()
}
Fragment.kt
#AndroidEntryPoint
#ExperimentalCoroutinesApi
class SettingsFragment : BaseBottomTabFragment() {
private var _binding: FragmentSettingsBinding? = null
private val binding get() = _binding!!
private val viewModel by viewModels<SettingViewModel>()
#Inject
lateinit var recyclerViewAdapter: RecyclerViewAdapter
#Inject
lateinit var bundle: Bundle
var finalList = mutableListOf<HomeRecyclerViewItems>()
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
// Inflate the layout for this fragment
_binding = FragmentSettingsBinding.inflate(layoutInflater,container,false)
val view = binding.root
binding.rvMovie.apply {
setHasFixedSize(true)
layoutManager = LinearLayoutManager(activity)
}
bundle.putString("Hello","hihg")
Toast.makeText(activity, "${bundle.getString("Hello")}", Toast.LENGTH_SHORT).show()
finalList.add(HomeRecyclerViewItems.Title(1,"hello"))
return view
}
private fun observeList() {
viewLifecycleOwner.lifecycleScope.launch {
viewLifecycleOwner.lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED){
launch {
viewModel.movieItems.collect { state ->
when(state){
is State.Loading ->{
}
is State.Success->{
if (state.data.isNotEmpty()){
recyclerViewAdapter = RecyclerViewAdapter()
binding.rvMovie.adapter = recyclerViewAdapter
recyclerViewAdapter.submitList(finalList)
}
}
is State.Error -> {
Toast.makeText(activity, "Error", Toast.LENGTH_SHORT).show()
}
else -> Unit
}
}
}
}
}
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
(activity as MainActivity).binding.ivSearch.isGone = true
viewModel.getHomeItemList()
observeList()
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
Note: I m following this tutorial simpliedCoding for api data for multirecyclerview but want to implement it with Kotlin State Flow. Any help in this regard is highly appreciated. Thanks.

Your problem is in here
val testList: Flow<State<List<HomeRecyclerViewItems.Movie>>> =
settingsRepo.getMovieList().map {
State.fromResource(it)
}
val directorList: Flow<State<List<HomeRecyclerViewItems.Directors>>> =
settingsRepo.getDirectorList().map {
State.fromResource(it)
}
_movieItem.value = combine(testList, directorList) { testList, directorList ->
testList + directorList
}
They are not returning a List<HomeRecyclerViewItems>, but a State<List<HomeRecyclerViewItems>. Maybe a better name for the variables are testsState and directorsState. After that it will be more clear why you need to unpack the values before combining the lists
_movieItem.value = combine(testsState, directorsState) { testsState, directorsState ->
val homeRecyclerViewItems = mutableListOf<HomeRecyclerViewItems>()
if (testsState is Success) homeRecyclerViewItems.add(testsState.data)
if (directorsState is Success) homeRecyclerViewItems.add(directorsState.data)
homeRecyclerViewItems
}

Android Room with LiveData + ViewModel Refresh Question

I have a small app I am using to try learn more about some of the newer Android components. I'm finding it difficult to find information and understand how best to do what I want.
Currently: Open app -> load data + stores in DB -> display data in list
I want to be able to query data again upon button press.
I have 2 buttons, 1 to fetch data again, 1 to delete the list data from the DB.
Problem is that it seems you cannot refresh if you are observing on an instance of LiveData, which I am. I understand that however the way I found to actually do a Network call and store in the Database returns an instance of LiveData and I am not sure how best to proceed.
Let me show you the code.
Fragment
private val viewModel: quoteViewModel by viewModels()
private lateinit var binding: FragmentHomeBinding
private lateinit var adapter: QuoteAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = FragmentHomeBinding.inflate(inflater, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
initRecyclerView()
setupRetrieveQuotesObserver()
setupDeleteDataListener()
setupFetchNewDataListener()
setupSwipeToRefresh()
}
private fun initRecyclerView() {
adapter = QuoteAdapter()
binding.recyclerView.layoutManager = LinearLayoutManager(requireContext())
binding.recyclerView.adapter = adapter
}
private fun setupDeleteDataListener() {
binding.removeQuotesButton.setOnClickListener {
viewModel.removeAllQuotes()
}
}
private fun setupFetchNewDataListener() {
binding.getQuotesButton.setOnClickListener {
viewModel.removeQuotes()
viewModel.getQuotes()
}
}
private fun setupRetrieveQuotesObserver() {
viewModel.quoteLiveDataList.observe(viewLifecycleOwner, Observer { result ->
when (result.status) {
NewResult.Status.SUCCESS -> {
result.data.let { adapter.setItems(ArrayList(result.data)) }
binding.progressBar.visibility = View.GONE
binding.swipeContainer.isRefreshing = false
}
NewResult.Status.ERROR -> {
binding.progressBar.visibility = View.GONE
Snackbar.make(binding.root, "Some error has occurred", Snackbar.LENGTH_SHORT)
.show()
}
NewResult.Status.LOADING -> {
binding.progressBar.visibility = View.VISIBLE
}
}
})
}
private fun setupSwipeToRefresh() {
binding.swipeContainer.setOnRefreshListener {
viewModel.getQuotes()
}
}
ViewModel
val quoteLiveDataList: LiveData<NewResult<List<Quote>>> = repository.quotes
fun getQuotes() = viewModelScope.launch {
repository.quotes
}
fun removeAllQuotes() = viewModelScope.launch {
repository.deleteAllQuotes()
}
Repository
val quotes = performGetOperation(
databaseQuery = { dao.getAllQuotes() },
networkCall = { remoteSource.getAllQuotes() },
saveCallResult = {
val quotesList = ArrayList<Quote>()
for (messageString in it.messages.non_personalized) {
quotesList.add(
Quote(
messageString,
FaceImageProvider().getRandomFacePicture(),
false
)
)
}
dao.insertQuotes(quotesList)
}
)
#WorkerThread
suspend fun deleteAllQuotes() = withContext(Dispatchers.IO) { dao.deleteAllQuotes() }
performGetOperation
This is a class I saw online for handling what I want to do. I think the issue stems from here as it is returning LiveData, I'm not sure how best to fix it
fun <T, A> performGetOperation(
databaseQuery: () -> LiveData<T>,
networkCall: suspend () -> NewResult<A>,
saveCallResult: suspend (A) -> Unit
): LiveData<NewResult<T>> =
liveData(Dispatchers.IO) {
emit(NewResult.loading())
val source = databaseQuery.invoke().map { NewResult.success(it) }
emitSource(source)
val responseStatus = networkCall.invoke()
if (responseStatus.status == NewResult.Status.SUCCESS) {
saveCallResult(responseStatus.data!!)
} else if (responseStatus.status == NewResult.Status.ERROR) {
emit(NewResult.error(responseStatus.message!!))
emitSource(source)
}
}
RemoteDataSource
suspend fun getQuotes() = getResult { service.getQuotes() }
getResult
protected suspend fun <T> getResult(call: suspend () -> Response<T>): NewResult<T> {
try {
val response = call.invoke()
if (response.isSuccessful) {
val body = response.body()
if (body != null) {
return NewResult.success(body)
}
}
return error("${response.code()} ${response.message()}")
} catch (e: Exception) {
return error(e.message ?: e.toString())
}
}
private fun <T> error(message: String): NewResult<T> {
Log.d("BaseDataSource", message)
return NewResult.error("Network called failed due to: $message")
}
NewResult
data class NewResult<out T>(val status: Status, val data: T?, val message: String?) {
enum class Status {
SUCCESS,
ERROR,
LOADING,
}
companion object {
fun <T> success(data: T): NewResult<T> {
return NewResult(Status.SUCCESS, data, null)
}
fun <T> error(message: String, data: T? = null): NewResult<T> {
return NewResult(Status.ERROR, data, message)
}
fun <T> loading(data: T? = null): NewResult<T> {
return NewResult(Status.LOADING, data, null)
}
}
Apologies for the very long message, but I guess I need to show all the little bits and bobs I'm using.
I think the problem is in the Fragment where I do viewModel.quoteLiveDataList.observe, as it is returning a new LiveData if it is called again. So I'm not sure how I can do another server call and update the DB and return it here.
Appreciate any help!
Thanks

Use Transformations.switchMap on a MutableLiveData to trigger your repository call like it is done here in the GithubBrowserSample project. This will allow you to implement the refresh functionality -
private val _getQuotes = MutableLiveData<Boolean>()
val quotes: LiveData<NewResult<List<Quote>>> = _getQuotes.switchMap { getQuotes ->
repository.quotes
}
fun getQuotes() {
_getQuotes.value = true
}
fun refresh() {
_getQuotes.value?.let {
_getQuotes.value = it
}
}

Android Paging Library Doesn't Scroll Up Correctly

I'm using the JetPack paging library with a network call (no database).
I am able to scroll down smoothly and load new pages of data, BUT, when scrolling up it stutters and quickly jumps to the top of the list. I am unable to scroll up smoothly.
Here is a video showing the problem: https://imgur.com/a/bRoelyF
What I've Tried:
Enabling retrofit caching
Using a LinearLayoutManager instead of GridLayoutManager
Following old and newer tutorials with versions 1.0.1 and 2.1.2 of the library
Here is my code:
MovieDataSource.kt:
private val movieDbApi: TheMovieDbApi
) : PageKeyedDataSource<Int, Movie>() {
override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Int, Movie>) {}
override fun loadInitial(params: LoadInitialParams<Int>, callback: LoadInitialCallback<Int, Movie>) {
movieDbApi.getTopRatedMovies(BuildConfig.MOVIE_DATA_BASE_API, FIRST_PAGE).subscribe(
{
it?.let { callback.onResult(it.results, null, FIRST_PAGE + 1) }
}, {}
)
}
override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, Movie>) {
movieDbApi.getTopRatedMovies(BuildConfig.MOVIE_DATA_BASE_API, params.key).subscribe(
{
val key = params.key + 1
it?.let {callback.onResult(it.results, key)
}
},{}
)
}
MovieDataSourceFactory.kt:
class MovieDataSourceFactory(private val movieDbApi: TheMovieDbApi) :
DataSource.Factory<Int, Movie>() {
// Is this where the MovieDataSource callBacks are sent?
val movieLiveDataSource = MutableLiveData<MovieDataSource>()
override fun create(): DataSource<Int, Movie> {
val movieDataSource = MovieDataSource(movieDbApi)
movieLiveDataSource.postValue(movieDataSource)
return movieDataSource
}
}
HomeViewModel.kt:
class HomeViewModel #Inject constructor(
theMovieDbApi: TheMovieDbApi
) : DisposingViewModel() {
var moviePagedList: LiveData<PagedList<Movie>>
private var liveDataSource: LiveData<MovieDataSource>
init {
val movieDataSourceFactory = MovieDataSourceFactory(theMovieDbApi)
liveDataSource = movieDataSourceFactory.movieLiveDataSource
val config = PagedList.Config.Builder()
.setEnablePlaceholders(true)
.setPageSize(MovieDataSource.PAGE_SIZE)
.build()
moviePagedList = LivePagedListBuilder(movieDataSourceFactory, config)
.build()
}
}
HomeViewModel.kt:
class HomeActivity : AppCompatActivity() {
#Inject
internal lateinit var viewModelFactory: ViewModelFactory<HomeViewModel>
private lateinit var viewModel: HomeViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_home)
AndroidInjection.inject(this)
val adapter = HomeAdapter()
movie_recycler_view.setHasFixedSize(false)
movie_recycler_view.layoutManager = LinearLayoutManager(this)
val viewModel = ViewModelProvider(this, viewModelFactory).get(HomeViewModel::class.java)
viewModel.moviePagedList.observe(this, Observer {
adapter.submitList(it)
})
movie_recycler_view.adapter = adapter
}
}
HomeAdapter.kt:
class HomeAdapter : PagedListAdapter<Movie, HomeAdapter.MovieViewHolder>(USER_COMPARATOR) {
override fun getItemCount(): Int {
return super.getItemCount()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MovieViewHolder {
val view = LayoutInflater.from(parent.context)
.inflate(R.layout.item_movie, parent, false)
return MovieViewHolder(view)
}
override fun onBindViewHolder(holder: MovieViewHolder, position: Int) {
val movie = getItem(position)
movie?.let { holder.bind(it) }
}
class MovieViewHolder(view: View) : RecyclerView.ViewHolder(view) {
fun bind(movie: Movie) {
Picasso.get().load(BASE_IMAGE_URL + movie.poster_path).into(itemView.movie_image)
}
}
companion object {
private val USER_COMPARATOR = object : DiffUtil.ItemCallback<Movie>() {
override fun areItemsTheSame(oldItem: Movie, newItem: Movie): Boolean =
oldItem.id == newItem.id
override fun areContentsTheSame(oldItem: Movie, newItem: Movie): Boolean =
oldItem == newItem
}
}
}
If anyone has a solution or spots a problem I'd love to hear it!

I solved the problem.
It's because I didn't add a placeholder image to Picasso in the adapter.
Before:
Picasso.get()
.load(BASE_IMAGE_URL + movie.poster_path)
.into(itemView.movie_image)
After:
Picasso.get()
.load(BASE_IMAGE_URL + movie.poster_path)
.placeholder(R.drawable.placeholder)
.into(itemView.movie_image)
Now it loads well.
Another consideration is the size of the image, it takes a while to load a larger image especially if you are loading many of them within an infinite scroll.

How to Update item values without changing the whole List?

I'm working on a Grid RecyclerView for Scores App. Scores will be updated every 5 secs from API Call...
I'm using this library for my Recyclerview Adapter.
I'm using Observable Fields & List.
I need to update only the scores (textviews) but now the RecyclerView is getting updated every 5 secs.
Please Guide me in right direction. Thank you!
Full Code in Gist
class DashboardFragment : Fragment() {
private lateinit var dashboardViewModel: DashboardViewModel
private lateinit var binding: FragmentDashboardBinding
lateinit var retrofit: Retrofit
lateinit var apiService: APIService
lateinit var disposable: Disposable
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
dashboardViewModel = ViewModelProvider(this).get(DashboardViewModel::class.java)
fetchData()
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = DataBindingUtil
.inflate(inflater, R.layout.fragment_dashboard, container, false)
binding.viewModel = dashboardViewModel
return binding.root
}
fun fetchData() {
val interceptor = HttpLoggingInterceptor()
interceptor.setLevel(HttpLoggingInterceptor.Level.BODY)
val client = OkHttpClient.Builder()
.addInterceptor(interceptor)
.connectTimeout(30, TimeUnit.SECONDS)
.readTimeout(30, TimeUnit.SECONDS)
.writeTimeout(30, TimeUnit.SECONDS)
.build()
val gson = GsonBuilder()
.setLenient()
.create()
retrofit = Retrofit.Builder()
.baseUrl(APIService.BASE_URL)
.client(client)
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create(gson))
.build()
apiService = this.retrofit.create(APIService::class.java)
callIndicesEndpoint(null)
disposable = Observable.interval(1000, 2000, TimeUnit.MILLISECONDS)
.observeOn(AndroidSchedulers.mainThread())
.subscribe({ aLong: Long? -> this.refreshIndices(aLong)})
{ throwable: Throwable -> this.onError(throwable) }
}
#SuppressLint("CheckResult")
private fun callIndicesEndpoint(aLong: Long?) {
val observable =
apiService.indices
observable.subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread())
.map { result: ObservableArrayList<Indices> -> result }
.subscribe(
{ data: ObservableArrayList<Indices> ->
this.handleResults(data)
}
) { t: Throwable ->
this.handleError(t)
}
}
#SuppressLint("CheckResult")
private fun refreshIndices(aLong: Long?) {
val observable =
apiService.indices
observable.subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread())
.map { result: ObservableArrayList<Indices> -> result }
.subscribe({ data: ObservableArrayList<Indices> -> this.refreshResults(data)})
{ t: Throwable ->this.handleError(t)}
}
private fun handleResults(data: ObservableArrayList<Indices>) {
dashboardViewModel.populate(data)
}
private fun refreshResults(data: ObservableArrayList<Indices>) {
dashboardViewModel.refresh(data)
}
private fun onError(throwable: Throwable) {
Log.e(">>>", "ERROR")
}
private fun handleError(t: Throwable) {
Log.e("> >", t.localizedMessage + " - Err - " + t.cause)
//Add your error here.
}
override fun onPause() {
super.onPause()
disposable.dispose()
}
}
VIEWMODEL
class DashboardViewModel : ViewModel() {
val indices: ObservableList<Indices> = ObservableArrayList<Indices>()
fun populate(data: ArrayList<Indices>) {
indices.clear()
indices.addAll(data)
}
fun refresh(data: ArrayList<Indices>) {
// How to refresh only Items without recreating the List
}
val itemIds: ItemIds<Any> =
ItemIds { position, item -> position.toLong() }
val indicesItem: ItemBinding<Indices> =
ItemBinding.of<Indices>(BR.item, R.layout.item_futures)
}

You can use broadcast receiver functionality for update particular items from recyclerview .

I think what you need is to use DiffUtil, it'll be of great help as
DiffUtil figures out what has changed, RecyclerView can use that information to update only the items that were changed, added, removed, or moved, which is much more efficient than redoing the entire list.
Here is a course you can use to get a hand of it: https://codelabs.developers.google.com/codelabs/kotlin-android-training-diffutil-databinding/#3

When I had something like that I used the DiffUtil.
I had to update rates every X seconds and not change the whole list.
So the adapter should be something like this:
class RatesAdapter :
ListAdapter<Rate, RecyclerView.ViewHolder>(RateDiffCallback()) {
private val baseRateView = 0
private val rateView = 1
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
return if (viewType == rateView) {
RateHolder(
RateItemBinding.inflate(
LayoutInflater.from(parent.context), parent, false
)
)
} else {
BaseRateHolder(
BaseRateLayoutBinding.inflate(
LayoutInflater.from(parent.context), parent, false
)
)
}
}
override fun getItemViewType(position: Int): Int {
return if (position == 0) {
baseRateView
} else rateView
}
override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
val rate = getItem(position)
if (holder.itemViewType == rateView) {
(holder as RateHolder).bind(rate)
holder.itemView.setOnClickListener {
swapper.itemSwap(rate)
}
} else {
(holder as BaseRateHolder).bind(rate)
}
}
class RateHolder(
private val binding: RateItemBinding
) : RecyclerView.ViewHolder(binding.root) {
fun bind(item: Rate) {
binding.apply {
rate = item
executePendingBindings()
}
}
}
class BaseRateHolder(
private val binding: BaseRateLayoutBinding
) : RecyclerView.ViewHolder(binding.root) {
fun bind(item: Rate) {
binding.apply {
rate = item
executePendingBindings()
}
}
val value = binding.value
}
}
private class RateDiffCallback : DiffUtil.ItemCallback<Rate>() {
override fun areItemsTheSame(oldItem: Rate, newItem: Rate): Boolean {
return oldItem.currencyCode == newItem.currencyCode
}
override fun areContentsTheSame(oldItem: Rate, newItem: Rate): Boolean {
return oldItem.rate == newItem.rate
}
}
Here I used binding in the adapter, and if you are not familiar with it, I will be more than happy to explain as well
In the Activity:
Before the onCreate:
private val ratesAdapter = RatesAdapter()
In the onCreate:
ratesList.adapter = ratesAdapter
Whenever you need to update the adapter including the first time you need to call it:
ratesAdapter.submitList(rates)
Rate is the model class that I am using
rates is the mutable list of < Rate >
ratesList is the recyclerview

try this : notifyItemChanged
with this:
listView.setItemAnimator(null);

Android RxJava Retrofit MVVM RecyclerView does not show up

I am implementing a RecyclerView in a fragment. The XML should be correct since I tried it with my hard-coded data, and the API call does return the correct json data from the server according to the Log in the console. The problem is that the RecyclerView adapter does not get any data from my Observable. Here is my implementation
In PostDataService interface I used Retrofit to get an Observable>
interface PostDataService {
#GET(".")
fun getPosts(
#Query(value = "offset") offset: Long = 0,
#Query(value = "limit") limit: Long = 10,
#Query(value = "subscribedOnly") subscribedOnly: Boolean = false
): Observable<List<Post>>
companion object {
val retrofit: PostDataService = Retrofit.Builder()
.baseUrl("http:aws/api/post/")
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.addConverterFactory(MoshiConverterFactory.create())
.client(client)
.build()
.create(PostDataService::class.java)
}
}
In PostListRepository, I used RxJava operators to get the LiveData
class PostListRepository {
private val postListLiveData: MutableLiveData<List<Post>> = MutableLiveData()
private val compositeDisposable: CompositeDisposable = CompositeDisposable()
fun getPostListLiveData(): MutableLiveData<List<Post>> {
val postList: MutableList<Post> = ArrayList()
val retrofitInstance = PostDataService.retrofit
val postListObservable = retrofitInstance.getPosts()
compositeDisposable.add(
postListObservable
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.flatMapIterable { it }
.subscribeWith(object : DisposableObserver<Post>() {
override fun onError(e: Throwable) {
// if some error happens in our data layer our app will not crash, we will
// get error here
}
override fun onNext(post: Post) {
postList.add(post)
}
override fun onComplete() {
postListLiveData.postValue(postList)
}
})
)
return postListLiveData
}
fun clear() {
compositeDisposable.clear()
}
}
In PostListViewModel, I passed the LiveData from the repository into this ViewModel.
class PostListViewModel : ViewModel() {
private var postListRepository: PostListRepository = PostListRepository()
fun getPostList(): MutableLiveData<List<Post>> {
return postListRepository.getPostListLiveData()
}
fun clear() {
postListRepository.clear()
}
}
Here is the Fragment that contains the RecyclerView. I think the .oberserve function in getPostList() is not called since I tried Log it but got nothing.
class PostListFragment : Fragment() {
private lateinit var recyclerView: RecyclerView
private lateinit var swipeLayout: SwipeRefreshLayout
private lateinit var postListViewModel: PostListViewModel
private val postListAdapter = PostRecyclerViewAdapter()
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val rootView = inflater.inflate(R.layout.view_post_list, container, false)
recyclerView = rootView.findViewById(R.id.postRecyclerView)
recyclerView.apply {
setHasFixedSize(true)
addItemDecoration(VerticalSpaceItemDecoration(36))
layoutManager = LinearLayoutManager(context)
adapter = postListAdapter
}
postListViewModel = ViewModelProviders.of(this).get(PostListViewModel::class.java)
getPostList()
swipeLayout = rootView.findViewById(R.id.swipeLayout)
swipeLayout.setColorSchemeResources(R.color.colorPrimary)
swipeLayout.setOnRefreshListener {
getPostList()
swipeLayout.isRefreshing = false
}
return rootView
}
override fun onDestroy() {
super.onDestroy()
postListViewModel.clear() // to avoid memory leak
}
private fun getPostList() {
postListViewModel.getPostList().observe(this, Observer<List<Post>> { resource ->
postListAdapter.setPostList(resource)
postListAdapter.notifyDataSetChanged()
})
}
}
Here is the adapter for the RecyclerView:
class PostRecyclerViewAdapter : RecyclerView.Adapter<PostViewHolder>() {
private var postList: List<Post> = ArrayList()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PostViewHolder {
// create a new view
val postView = PostView(parent.context)
// set the view's size, margins, paddings and layout parameters
return PostViewHolder.from(postView)
}
override fun getItemCount(): Int = postList.size
override fun onBindViewHolder(holder: PostViewHolder, position: Int) {
val curPost = postList[position]
holder.postView.apply {
setPostOwnerDisplayName(curPost.content.userDisplayedName)
setPostOwnerRole(curPost.content.role)
setPostOwnerAvatar(R.mipmap.ic_launcher_round)
setPostText(curPost.content.text)
setPostImage(curPost.content.smallMediaPaths[0])
setLikeState(curPost.liked)
setBookmarkState(curPost.bookmarked)
}
}
fun setPostList(postList: List<Post>) {
this.postList = postList
}
}
As I mentioned above, I think the .oberserve function in getPostList() in PostListFragment is not called since I tried Log it but got nothing, so there is no data passed into the RecyclerView. Can anyone help me find the reason why it's not being called, or why it's not getting the data from the ViewModel?

I wouldn't think of this is related to your issue, but your code has potential problems.
To move observe part to onActivityCreated would be better to ensure view is created.
when your fragment view is re-created, a new Observer will be added, while previous one still alive, because your Observer is anonymous. So, you have to manage the observers to prevent it.

I just found out that I forgot to catch the exception in RxJava onNext() in case to get the moshi serialization error. After getting that, I got some moshi conversion errors.
Posted it in case anyone carelessly forgot to catch the moshi error.
Thanks!