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Android - I can access ViewModel method from fragment but the method does not return the list

I recently started studying android kotlin and I am expecting this to have a very simple answer but I have a ViewModel which has a method called getDataComment and I want to call the method from my fragment and provide the needed argument for it. But when I try to call it, there's no build error, it just doesn't show the list.
My method in view model:
fun getDataComment(postId: Int) {
PostRepository().getDataComment(postId).enqueue(object : Callback<List<Comment>>{
override fun onResponse(call: Call<List<Comment>>, response: Response<List<Comment>>) {
val comments = response.body()
comments?.let {
mPostsComment.value = comments!!
}
}
override fun onFailure(call: Call<List<Comment>>, t: Throwable) {
Log.e(TAG, "On Failure: ${t.message}")
t.printStackTrace()
}
})
}
Fragment Class
class PostDetailFragment : Fragment() {
var param2: Int = 0
private lateinit var binding: FragmentPostDetailBinding
private val viewModel by viewModels<PostCommentViewModel>()
private val gson: Gson by lazy {
Gson()
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
binding =
DataBindingUtil.inflate(inflater, R.layout.fragment_post_detail, container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
checkArguments()
}
private fun checkArguments() {
arguments?.let { bundle ->
if (bundle.containsKey("POST")) {
val postString = bundle.getString("POST", "")
val post: Post = gson.fromJson(postString, Post::class.java)
binding.postDetailstvTitle.text = post.title
binding.postDetailstvBody.text = post.body
param2 = post.id
viewModel.getDataComment(param2)
}
}
}
}
Here's what it's supposed to look like: 1
Here's what I'm getting: 2
Sorry in advance if It's messy this is my first time asking here and let me know if you need more information. Thank you!

observe mPostsComment inside fragment from viewmodel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
checkArguments()
viewModel.mPostsComment.observe(viewLifecycleOwner, { collectionList ->
// do whatever you want with collectionList
})
}

Live Data Observer called only once. It is not updating the data from server when api is called again to update UI

I looked for many articles and tried to understand how Live Data is observe changes when MVVM architecture is used.
I have a Fragment A, ViewModel and Repository class.
ViewModel is initiated in onCreateView() method of the fragment.
Api call is initiated just after that in onCreateView() method of fragment.
Data from the Server is observed in onViewCreated method of the fragment.
For the first, it is running perfectly fine. But When I update the user name from another Fragment B and come back to Fragment A.
Api is called again in onResume() method of Fragment A to update UI. But here my Live Data is not observed again and UI is not updated
I didn't understand what I am doing wrong? Why observer is not triggering second time?
Below is the code
class FragmentA : Fragment(){
private lateinit var dealerHomeViewModel: DealerHomeViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_home_dealers, container, false)
val dealerHomeFactory = DealerHomeFactory(token!!)
dealerHomeViewModel = ViewModelProvider(this,dealerHomeFactory).get(DealerHomeViewModel::class.java)
dealerHomeViewModel.getDealerHomeData()
return view
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
dealerHomeViewModel.dealerInfoLiveData.observe(viewLifecycleOwner, androidx.lifecycle.Observer {dealerInfo ->
// Update UI
tvDealerName.text = dealerInfo.name
})
}
override fun onResume() {
super.onResume()
dealerHomeViewModel.getDealerHomeData()
}
}
//=========================== VIEW MODEL ===================================//
class DealerHomeViewModel(val token:String) : ViewModel() {
var dealerInfoLiveData:LiveData<DealerInfo>
init {
dealerInfoLiveData = MutableLiveData()
}
fun getDealerHomeData(){
dealerInfoLiveData = DealerHomeRepo().getDealerHomePageInfo(token)
}
}
//======================== REPOSITORY ================================//
class DealerHomeRepo {
fun getDealerHomePageInfo(token:String):LiveData<DealerInfo>{
val responseLiveData:MutableLiveData<DealerInfo> = MutableLiveData()
val apiCall: ApiCall? = RetrofitInstance.getRetrofit()?.create(ApiCall::class.java)
val dealerInfo: Call<DealerInfo>? = apiCall?.getDealerInfo(Constants.BEARER+" "+token,Constants.XML_HTTP)
dealerInfo?.enqueue(object : Callback<DealerInfo>{
override fun onFailure(call: Call<DealerInfo>, t: Throwable) {
Log.d(Constants.TAG,t.toString())
}
override fun onResponse(call: Call<DealerInfo>, response: Response<DealerInfo>) {
if(response.isSuccessful){
when(response.body()?.status){
Constants.SUCCESS -> {
responseLiveData.value = response.body()
}
Constants.FAIL -> {
}
}
}
}
})
return responseLiveData
}
}

I think your problem is that you are generating a NEW mutableLiveData each time you use your getDealerHomePageInfo(token:String method.
First time you call getDealerHomePageInfo(token:String) you generate a MutableLiveData and after on onViewCreated you observe it, it has a value.
In onResume, you call again getDealerHomePageInfo(token:String) that generates a NEW MutableLiveData so your observer is pointing to the OLD one.
What would solve your problem is to pass the reference of your viewModel to your repository so it updates the MutableLiveData with each new value, not generate a new one each time.
Edited Answer:
I would do something like this for ViewModel:
class DealerHomeViewModel(val token:String) : ViewModel() {
private val _dealerInfoLiveData:MutableLiveData<DealerInfo> = MutableLiveData()
val dealerInfoLiveData:LiveData = _dealerInfoLiveData
fun getDealerHomeData(){
DealerHomeRepo().getDealerHomePageInfo(token, _dealerInfoLiveData)
}
}
And this for the DealerHomeRemo
class DealerHomeRepo{
fun getDealerHomePageInfo(token:String, liveData: MutableLiveData<DealerInfo>){
val apiCall: ApiCall? = RetrofitInstance.getRetrofit()?.create(ApiCall::class.java)
val dealerInfo: Call<DealerInfo>? = apiCall?.getDealerInfo(Constants.BEARER+" "+token,Constants.XML_HTTP)
dealerInfo?.enqueue(object : Callback<DealerInfo>{
override fun onFailure(call: Call<DealerInfo>, t: Throwable) {
Log.d(Constants.TAG,t.toString())
}
override fun onResponse(call: Call<DealerInfo>, response: Response<DealerInfo>) {
if(response.isSuccessful){
when(response.body()?.status){
Constants.SUCCESS -> {
liveData.value = response.body()
}
Constants.FAIL -> {
}
}
}
}
})
}
For Observers, use the LiveData as before:
dealerHomeViewModel.dealerInfoLiveData.observe(viewLifecycleOwner, androidx.lifecycle.Observer {dealerInfo ->
// Update UI
tvDealerName.text = dealerInfo.name
})

Cannot get the same instance of a scoped component - Dagger 2 Clean architecture

I'm using Dagger 2 in clean architecture project, I have 2 fragments. These 2 fragments should be scoped together to share the same instances, but unfortunately, I got empty object in the second fragment.
Application Component
#ApplicationScope
#Component(modules = [ContextModule::class, RetrofitModule::class])
interface ApplicationComponent {
fun exposeRetrofit(): Retrofit
fun exposeContext(): Context
}
Data layer - Repository
class MoviesParsableImpl #Inject constructor(var moviesLocalResult: MoviesLocalResult): MoviesParsable {
private val TAG = javaClass.simpleName
private val fileUtils = FileUtils()
override fun parseMovies() {
Log.d(TAG,"current thread is ".plus(Thread.currentThread().name))
val gson = Gson()
val fileName = "movies.json"
val jsonAsString = MyApplication.appContext.assets.open(fileName).bufferedReader().use{
it.readText()
}
val listType: Type = object : TypeToken<MoviesLocalResult>() {}.type
moviesLocalResult = gson.fromJson(jsonAsString,listType)
Log.d(TAG,"result size ".plus(moviesLocalResult.movies?.size))
}
override fun getParsedMovies(): Results<MoviesLocalResult> {
return Results.Success(moviesLocalResult)
}
}
Repo Module
#Module
interface RepoModule {
#DataComponentScope
#Binds
fun bindsMoviesParsable(moviesParsableImpl: MoviesParsableImpl): MoviesParsable
}
MoviesLocalResultsModule(the result need its instance across different fragments)
#Module
class MoviesLocalResultModule {
#DataComponentScope
#Provides
fun provideMovieLocalResults(): MoviesLocalResult{
return MoviesLocalResult()
}
}
Use case
class AllMoviesUseCase #Inject constructor(private val moviesParsable: MoviesParsable){
fun parseMovies(){
moviesParsable.parseMovies()
}
fun getMovies(): Results<MoviesLocalResult> {
return moviesParsable.getParsedMovies()
}
}
Presentation Component
#PresentationScope
#Component(modules = [ViewModelFactoryModule::class],dependencies = [DataComponent::class])
interface PresentationComponent {
fun exposeViewModel(): ViewModelFactory
}
First ViewModel, where I got the result to be shared with the other fragment when needed
class AllMoviesViewModel #Inject constructor(private val useCase: AllMoviesUseCase):ViewModel() {
private val moviesMutableLiveData = MutableLiveData<Results<MoviesLocalResult>>()
init {
moviesMutableLiveData.postValue(Results.Loading())
}
fun parseJson(){
viewModelScope.launch(Dispatchers.Default){
useCase.parseMovies()
moviesMutableLiveData.postValue(useCase.getMovies())
}
}
fun readMovies(): LiveData<Results<MoviesLocalResult>> {
return moviesMutableLiveData
}
}
Second ViewModel where no need to request data again as it's expected to be scoped
class MovieDetailsViewModel #Inject constructor(private val useCase: AllMoviesUseCase): ViewModel() {
var readMovies = liveData(Dispatchers.IO){
emit(Results.Loading())
val result = useCase.getMovies()
emit(result)
}
}
First Fragment, where data should be requested:
class AllMoviesFragment : Fragment() {
private val TAG = javaClass.simpleName
private lateinit var viewModel: AllMoviesViewModel
private lateinit var adapter: AllMoviesAdapter
private lateinit var layoutManager: LinearLayoutManager
private var ascendingOrder = true
#Inject
lateinit var viewModelFactory: ViewModelFactory
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setHasOptionsMenu(true)
DaggerAllMoviesComponent.builder()
.presentationComponent(
DaggerPresentationComponent.builder()
.dataComponent(
DaggerDataComponent.builder()
.applicationComponent(MyApplication.applicationComponent).build()
)
.build()
).build()inject(this)
viewModel = ViewModelProvider(this, viewModelFactory).get(AllMoviesViewModel::class.java)
startMoviesParsing()
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_all_movies, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
setupRecyclerView()
viewModel.readMovies().observe(viewLifecycleOwner, Observer {
if (it != null) {
when (it) {
is Loading -> {
showResults(false)
}
is Success -> {
showResults(true)
Log.d(TAG, "Data observed ".plus(it.data))
addMoviesList(it.data)
}
is Error -> {
moviesList.snack(getString(R.string.error_fetch_movies))
}
}
}
})
}
Second Fragment, where I expect to get the same instance request in First Fragment as they are scoped.
class MovieDetailsFragment: Fragment() {
val TAG = javaClass.simpleName
#Inject
lateinit var viewModelFactory: ViewModelFactory
lateinit var viewModel: MovieDetailsViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
val depend = DaggerAllMoviesComponent.builder()
.presentationComponent(
DaggerPresentationComponent.builder()
.dataComponent(
DaggerDataComponent.builder()
.applicationComponent(MyApplication.applicationComponent).build())
.build()
).build()
depend.inject(this)
viewModel = ViewModelProvider(this, viewModelFactory).get(MovieDetailsViewModel::class.java)
}
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
viewModel.readMovies.observe(this, Observer {
if (it!=null){
Log.d(TAG,"Movies returned successfully")
}
})
return super.onCreateView(inflater, container, savedInstanceState)
}
}

Scopes tell a component to cache the results of a binding. It has nothing to do with caching instances of any components. As such, you are always creating a new DataComponent, PresentationComponent, and AllMoviesComponent in your fragments' onCreate methods.
In order to reuse the same AllMoviesComponent instance, you need to store it somewhere. Where you store it can depend on your app architecture, but some options include MyApplication itself, the hosting Activity, or in your navigation graph somehow.
Even after fixing this, you can't guarantee that parseMovies has already been called. The Android system could kill your app at any time, including when MoviesDetailFragment is the current fragment. If that happens and the user navigates back to your app later, any active fragments will be recreated, and you'll still get null.

Live data giving old value again while changing fragment

I am using live data from a shared ViewModel across multiple fragments. I have a sign-in fragment which takes user's phone number and password and then the user presses sign in button I am calling the API for that, now if the sign-in fails I am showing a toast "Sign In failed", now if the user goes to "ForgotPassword" screen which also uses the same view model as "SignInFragment" and presses back from the forgot password screen, it comes to sign-in fragment, but it again shows the toast "Sign In failed" but the API is not called, it gets data from the previously registered observer, so is there any way to fix this?
SignInFragment.kt
class SignInFragment : Fragment() {
private lateinit var binding: FragmentSignInBinding
//Shared view model across two fragments
private val onBoardViewModel by activityViewModels<OnBoardViewModel>()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = DataBindingUtil.inflate(
inflater,
R.layout.fragment_sign_in,
container,
false
)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
onBoardViewModel.signInResponse.observe(viewLifecycleOwner) { response ->
//This is calling again after coming back from new fragment it.
showToast("Sign In Failed")
}
}
override fun onClick(v: View?) {
when (v?.id!!) {
R.id.forgotPasswordTV -> {
findNavController().navigate(SignInFragmentDirections.actionSignInFragmentToForgotPasswordFragment())
}
R.id.signInTV -> {
val phoneNumber = binding.phoneNumberET.text
val password = binding.passwordET.text
val signInRequestModel = SignInRequestModel(
phoneNumber.toString(),
password.toString(),
""
)
//Calling API for the sign-in
onBoardViewModel.callSignInAPI(signInRequestModel)
}
}
}
}
ForgotPasswordFragment
class ForgotPasswordFragment : Fragment() {
private lateinit var binding: FragmentForgotPasswordBinding
//Shared view model across two fragments
private val onBoardViewModel by activityViewModels<OnBoardViewModel>()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
binding = DataBindingUtil.inflate(
inflater,
R.layout.fragment_forgot_password,
container,
false
)
return binding.root
}
}
OnBoardViewModel
class OnBoardViewModel : ViewModel() {
private var repository: OnBoardRepository = OnBoardRepository.getInstance()
private val signInRequestLiveData = MutableLiveData<SignInRequestModel>()
//Observing this data in sign in fragment
val signInResponse: LiveData<APIResource<SignInResponse>> =
signInRequestLiveData.switchMap {
repository.callSignInAPI(it)
}
//Calling this function from sign in fragment
fun callSignInAPI(signInRequestModel: SignInRequestModel) {
signInRequestLiveData.value = signInRequestModel
}
override fun onCleared() {
super.onCleared()
repository.clearRepo()
}
}
I have tried to move this code inside onActivityCreated but it's still getting called after coming back from new fragment.
onBoardViewModel.signInResponse.observe(viewLifecycleOwner) { response ->
showToast("Sign In Failed")
}

Using SingleLiveEvent class instead of LiveData in OnBoardViewModel class will solve your problem:
val signInResponse: SingleLiveEvent <APIResource<SignInResponse>>.
class SingleLiveEvent<T> : MutableLiveData<T>() {
private val pending = AtomicBoolean(false)
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
super.observe(owner, Observer<T> { t ->
if (pending.compareAndSet(true, false)) {
observer.onChanged(t)
}
})
}
override fun setValue(t: T?) {
pending.set(true)
super.setValue(t)
}
fun call() {
postValue(null)
}
}
This is a lifecycle-aware observable that sends only new updates after subscription. This LiveData only calls the observable if there's an explicit call to setValue() or call().

I would provide a way to reset your live data. Give it a nullable type. Your observers can ignore it when they get a null value. Call this function when you receive login data, so you also won't be repeating messages on a screen rotation.
class OnBoardViewModel : ViewModel() {
// ...
fun consumeSignInResponse() {
signInRequestLiveData.value = null
}
}
onBoardViewModel.signInResponse.observe(viewLifecycleOwner) { response ->
if (response != null) {
showToast("Sign In Failed")
onBoardViewModel.consumeSignInResponse()
}
}

For Kotlin users #Sergey answer can also be implemented using delegates like below
class SingleLiveEvent<T> : MutableLiveData<T>() {
var curUser: Boolean by Delegates.vetoable(false) { property, oldValue, newValue ->
newValue != oldValue
}
override fun observe(owner: LifecycleOwner, observer: Observer<in T>) {
super.observe(owner, Observer<T> { t ->
if (curUser) {
observer.onChanged(t)
curUser = false
}
})
}
override fun setValue(t: T?) {
curUser = true
super.setValue(t)
}
fun call() {
postValue(null)
}
}

LiveData not working until user performs some action

My LiveData is not working.
ViewModel:
private var _email = MutableLiveData<String>()
fun setEmail(){
_email.postValue("azizjon#bla.mn")
}
fun getEmail(): LiveData<String>{
return _email
}
Fragment's onViewCreated method
:
mViewModel.getEmail().observe(viewLifecycleOwner, Observer {
tvEmail.text = it
})
mViewModel.setEmail() //Trying to post data to my LiveData.
The above code is not working as tvEmail is not chaning.
However, if I trust a button for posting data to LiveData like this, it is working:
//Inside fragment again
button.setOnClickListener {
mViewModel.setEmail()
}
When user clicks button, text in tvEmail is changing. If user does not click, nothing is happening. What am I missing here?
Edit:
I have just tested the code with Activity. Surprisingly, for Activitys it is working but not for Fragments.

#Azizjon Kholmatov - Best practice you can write your code inside the "onActivityCreated" function
please refer this. If you still having the problem let me know in comments section. I am happy to help. :)
class MainFragment : Fragment() {
companion object {
fun newInstance() = MainFragment()
}
private lateinit var viewModel: MainViewModel
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
return inflater.inflate(R.layout.main_fragment, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
viewModel.getEmail().observe(viewLifecycleOwner, Observer {
tvEmail.text = it
})
viewModel.setEmail("first#email.com")
button.setOnClickListener {
viewModel.setEmail("clicked#email.com")
}
}
}
And ViewModel class as follows
class MainViewModel : ViewModel() {
private var _email = MutableLiveData<String>()
fun setEmail(email: String = "example#email.com") {
_email.postValue(email)
}
fun getEmail(): LiveData<String> {
return _email
}
}