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Shared ViewModel Not Working With Bottom Sheet Dialog Fragment, DB and UI

i have a really simple vocabulary note app contains 2 fragment and 1 root activity. In HomeFragment i have a button "addVocabularyButton". When it is clicked a BottomSheetDialogFragment appears and user gives 3 inputs and with a viewmodel it is saved in DB. My problem is when i save the input to the DB it works fine but i cannot see in HomeFragment that word instantaneously. I have to re-run the app to see in home fragment. I am using Navigation library and recycler view in home fragment.
Github link : https://github.com/ugursnr/MyVocabularyNotebook
Home Fragment
class HomeFragment : Fragment() {
private var _binding : FragmentHomeBinding? = null
private val binding get() = _binding!!
private var vocabularyAdapter = VocabulariesHomeAdapter()
private lateinit var sharedViewModel: AddVocabularySharedViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentHomeBinding.inflate(layoutInflater,container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//sharedViewModel = ViewModelProvider(this)[AddVocabularySharedViewModel::class.java]
sharedViewModel = (activity as MainActivity).sharedViewModel
sharedViewModel.getAllVocabulariesFromDB()
observeAllVocabularies()
prepareRecyclerView()
addVocabularyOnClick()
vocabularyAdapter.onItemDeleteClicked = {
sharedViewModel.deleteVocabulary(it)
observeAllVocabularies()
}
}
private fun prepareRecyclerView(){
binding.recyclerViewHome.apply {
layoutManager = LinearLayoutManager(context)
adapter = vocabularyAdapter
}
}
private fun addVocabularyOnClick(){
binding.addVocabularyButton.setOnClickListener{
val action = HomeFragmentDirections.actionHomeFragmentToAddVocabularyBottomSheetFragment()
Navigation.findNavController(it).navigate(action)
}
}
private fun observeAllVocabularies(){
sharedViewModel.allVocabulariesLiveData.observe(viewLifecycleOwner, Observer {
vocabularyAdapter.updateVocabularyList(it)
})
}
}
Dialog Fragment
class AddVocabularyBottomSheetFragment : BottomSheetDialogFragment() {
private var _binding : FragmentAddVocabularyBottomSheetBinding? = null
private val binding get() = _binding!!
private lateinit var sharedViewModel: AddVocabularySharedViewModel
private var vocabularyInput : String? = null
private var translationInput : String? = null
private var sampleSentenceInput : String? = null
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentAddVocabularyBottomSheetBinding.inflate(layoutInflater,container,false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//sharedViewModel = ViewModelProvider(this)[AddVocabularySharedViewModel::class.java]
sharedViewModel = (activity as MainActivity).sharedViewModel
binding.addOrUpdateVocabularyButton.setOnClickListener {
vocabularyInput = binding.vocabularyActualET.text.toString()
translationInput = binding.vocabularyTranslationET.text.toString()
sampleSentenceInput = binding.vocabularySampleSentenceET.text.toString()
val inputVocabulary = Vocabulary(vocabularyInput,translationInput,sampleSentenceInput)
insertVocabularyToDB(inputVocabulary)
sharedViewModel.getAllVocabulariesFromDB()
dismiss()
}
}
private fun insertVocabularyToDB(vocabulary: Vocabulary){
sharedViewModel.insertVocabulary(vocabulary)
}
}
Shared ViewModel
class AddVocabularySharedViewModel(application: Application) : AndroidViewModel(application) {
private var _allVocabulariesLiveData = MutableLiveData<List<Vocabulary>>()
private var _vocabularyLiveData = MutableLiveData<Vocabulary>()
val allVocabulariesLiveData get() = _allVocabulariesLiveData
val vocabularyLiveData get() = _vocabularyLiveData
val dao = VocabularyDatabase.makeDatabase(application).vocabularyDao()
val repository = VocabularyRepository(dao)
fun insertVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.insertVocabulary(vocabulary)
}
fun updateVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.updateVocabulary(vocabulary)
}
fun deleteVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.deleteVocabulary(vocabulary)
}
fun getAllVocabulariesFromDB() = CoroutineScope(Dispatchers.IO).launch {
val temp = repository.getAllVocabulariesFromDB()
withContext(Dispatchers.Main){
_allVocabulariesLiveData.value = temp
}
}
fun getVocabularyDetailsByID(vocabularyID : Int) = CoroutineScope(Dispatchers.IO).launch {
val temp = repository.getVocabularyDetailsByID(vocabularyID).first()
withContext(Dispatchers.Main){
_vocabularyLiveData.value = temp
}
}
}
Adapter
class VocabulariesHomeAdapter : RecyclerView.Adapter<VocabulariesHomeAdapter.VocabulariesHomeViewHolder>() {
lateinit var onItemDeleteClicked : ((Vocabulary) -> Unit)
val allVocabulariesList = arrayListOf<Vocabulary>()
class VocabulariesHomeViewHolder(val binding : RecyclerRowBinding) : RecyclerView.ViewHolder(binding.root)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VocabulariesHomeViewHolder {
return VocabulariesHomeViewHolder(RecyclerRowBinding.inflate(LayoutInflater.from(parent.context), parent, false))
}
override fun onBindViewHolder(holder: VocabulariesHomeViewHolder, position: Int) {
val vocabulary = allVocabulariesList[position]
holder.binding.apply {
actualWordTV.text = vocabulary.vocabulary
translationWordTV.text = vocabulary.vocabularyTranslation
deleteButtonRV.setOnClickListener {
onItemDeleteClicked.invoke(vocabulary)
notifyItemRemoved(position)
}
}
}
override fun getItemCount(): Int {
return allVocabulariesList.size
}
fun updateVocabularyList(newList : List<Vocabulary>){
allVocabulariesList.clear()
allVocabulariesList.addAll(newList)
notifyDataSetChanged()
}
}
I know there are lots of codes up there but i have a really big problems about using these dialog fragments. Thank you for your help.

This is because multiple instances of the same View Model are created by the Navigation Library for each Navigation Screen.
You need to tell the Navigation Library to share the same ViewModel between all navigation screens.
Easiest way to fix this is to scope the viewModel to the Activity rather than a Fragment and using it in all your fragments.
val viewModel = ViewModelProvider(requireActivity()).get(MyViewModel::class.java)
This way, the viewModel is scoped to the Application instance rather than Fragment. This will keep the state in the viewModel persistent across the Application.
You can also do this by scoping the viewModel to the navigation graph.
val myViewModel: MyViewModel by navGraphViewModels(R.id.your_nested_nav_id)
Alternate method, if you're using dependency injection libraries
val navController = findNavController();
val navBackStackEntry = navController.currentBackStackEntry!!
If you use hilt, you can just pass your NavBackStackEntry of the NavGraph to hiltViewModel()
val viewModel = hiltViewModel<MyViewModel>(//pass NavBackStackEntry)
This will give you a viewModel that is scoped to NavBackStackEntry and will only be recreated when you pop the NavBackStackEntry(ie Navigate out of the navigation screens.)

How can I send a variable from a fragment to a view model in MVVM architecture in kotlin?

Well I am a beginner with android and kotlin so I have been trying to send a variable semesterSelected from the fragment ViewCourses to my viewmodel UserViewModel is the codes are down below.
`class ViewCourses(path: String) : ReplaceFragment() {
private var semesterSelected= path
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
container?.removeAllViews()
return inflater.inflate(R.layout.fragment_view_courses, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
userRecyclerView = view.findViewById(R.id.recyclerView)
userRecyclerView.layoutManager = LinearLayoutManager(context)
userRecyclerView.setHasFixedSize(true)
adapter = MyAdapter()
userRecyclerView.adapter = adapter
makeToast(semesterSelected)
// The variable I am trying to send to UserViewModel is -->> semesterSelected
var viewModel: UserViewModel = ViewModelProvider(this)[UserViewModel::class.java]
viewModel.allUsers.observe(viewLifecycleOwner) {
adapter.updateUserList(it)
}
}
}
class UserViewModel : ViewModel() {
private val repository: UserRepository = UserRepository("CSE/year3semester1").getInstance()
private val _allUsers = MutableLiveData<List<CourseData>>()
val allUsers: LiveData<List<CourseData>> = _allUsers
init {
repository.loadUsers(_allUsers)
}
}
The reason I am doing this is I am wanting a to send a variable to my repository UserRepository all the way from ViewCourses and thought sending this via UserViewModel might be a way .
class UserRepository(semesterSelected: String) {
// The variable I am expecting to get from UserViewModel
private var semesterSelected = semesterSelected
private val databaseReference: DatabaseReference =
FirebaseDatabase.getInstance().getReference("course-list/$semesterSelected")
#Volatile
private var INSTANCE: UserRepository? = null
fun getInstance(): UserRepository {
return INSTANCE ?: synchronized(this) {
val instance = UserRepository(semesterSelected)
INSTANCE = instance
instance
}
}
fun loadUsers(userList: MutableLiveData<List<CourseData>>) {
databaseReference.addValueEventListener(object : ValueEventListener {
override fun onDataChange(snapshot: DataSnapshot) {
try {
val courseList: List<CourseData> = snapshot.children.map { dataSnapshot ->
dataSnapshot.getValue(CourseData::class.java)!!
}
userList.postValue(courseList)
} catch (e: Exception) {
}
}
override fun onCancelled(error: DatabaseError) {
}
})
}
}
I tried something like below
class ViewCourses(path: String) : ReplaceFragment() {
private var semesterSelected= path
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
container?.removeAllViews()
return inflater.inflate(R.layout.fragment_view_courses, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
userRecyclerView = view.findViewById(R.id.recyclerView)
userRecyclerView.layoutManager = LinearLayoutManager(context)
userRecyclerView.setHasFixedSize(true)
adapter = MyAdapter()
userRecyclerView.adapter = adapter
makeToast(semesterSelected)
**// Sending the variable as parameter**
var viewModel: UserViewModel = ViewModelProvider(this)[UserViewModel(semesterSelected)::class.java]
viewModel.allUsers.observe(viewLifecycleOwner) {
adapter.updateUserList(it)
}
}
}
class UserViewModel(semesterSelected: String) : ViewModel() {
private val repository: UserRepository = UserRepository("CSE/year3semester1").getInstance()
private val _allUsers = MutableLiveData<List<CourseData>>()
val allUsers: LiveData<List<CourseData>> = _allUsers
init {
repository.loadUsers(_allUsers)
}
}
but doing this my app crashes . how can this be done ?
Thanks in Advance.

var viewModel: UserViewModel = ViewModelProvider(this)[UserViewModel(semesterSelected)::class.java]
UserViewModel(semesterSelected)::class.java NOR UserViewModel::class.java is a constructor for the view model.
If you would want to have ViewModel with that NEEDS initial parameters, you will have to create your own factory for that - which is a tad more complicated and for your case, it might be overkill for what you are trying to do but in the longterm it will pay off(Getting started with VM factories).
With that said, your needs can be easily solved by one function to initialize the view model.
class UserViewModel() : ViewModel() {
private lateinit var repository: UserRepository
private val _allUsers = MutableLiveData<List<CourseData>>()
val allUsers: LiveData<List<CourseData>> = _allUsers
fun initialize(semesterSelected: String) {
repository = UserRepository("CSE/year3semester1").getInstance()
repository.loadUsers(_allUsers)
}
}

A ViewModel must be created using a ViewModelProvider.Factory. But there is a default Factory that is automatically used if you don't specify one. The default factory can create ViewModels who have constructor signatures that are one of the following:
empty, for example MyViewModel: ViewModel.
saved state handle, for example MyViewModel(private val savedStateHandle: SavedStateHandle): ViewModel
application, for example MyViewModel(application: Application): AndroidViewModel(application)
both, for example MyViewModel(application: Application, private val savedStateHandle: SavedStateHandle): AndroidViewModel(application)
If your constructor doesn't match one of these four above, you must create a ViewModelProvider.Factory that can instantiate your ViewModel class and use that when specifying your ViewModelProvider. In Kotlin, you can use by viewModels() for easier syntax. All the instructions for how to create your ViewModelFactory are here.

LiveData observer not triggered

I want to navigate to an other Fragment when the user selcts a value (player id) in the AlertDialog. I use this change to the id to trigger the navigation. Unfortunately the observer of this property doesn't get triggerd.
Please see the following code:
SelectCharacterDialogFragment.kt
#AndroidEntryPoint
class SelectCharacterDialogFragment : DialogFragment() {
val viewModel: WelcomeViewModel by viewModels()
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
super.onCreateDialog(savedInstanceState)
val names = arguments?.getStringArrayList("names")
val ids = arguments?.getIntegerArrayList("ids")
val dialogBuilder = MaterialAlertDialogBuilder(requireContext())
.setTitle("Choose a character")
.setItems(names!!.toTypedArray()) { dialog, which ->
val playerId = ids?.get(which)
Timber.d("Selected player id: %d", playerId)
viewModel.setActivePlayerId(playerId!!)
}
return dialogBuilder.create()
}
}
WelcomeViewModel.kt
#HiltViewModel
class WelcomeViewModel #Inject constructor(private val repository: PlayerRepository) : ViewModel() {
private val _activePlayerId = MutableLiveData<Int>()
val playerId:LiveData<Int> =_activePlayerId
fun setActivePlayerId(playerId: Int){
setActivePlayer(playerId)
_activePlayerId.value =playerId
}
private fun setActivePlayer(playerId: Int) {
viewModelScope.launch {
repository.setActivePlayer(playerId)
Timber.d("Active player set to id: %d", playerId)
}
}
}
WelcomeFragment.kt
#AndroidEntryPoint
class WelcomeFragment : Fragment() {
private val viewModel: WelcomeViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
viewModel.playerId.observe(viewLifecycleOwner){
Timber.d("Observing active player id: %d", it)
findNavController().navigate(
WelcomeFragmentDirections.actionWelcomeFragmentToNavigationPlayer()
)
}
}
}
The last log output I see is from the method WelcomeViewModel#setActivePlayer(playerId: Int). Maybe it's obvious but I just can't figure out what's wrong with the code.

You've to use shared viewmodel.
Update your fragment and dialog as well
val viewModel: WelcomeViewModel by activityViewModels()

Android ViewModel instantiate twice using hilt

I have a parent fragment which fetches a list from API using ViewModel and Retrofit, the ViewModel is injected with Hilt.
After the list gets fetched the parent fragment will pass to its child fragment that is inside of parent fragment.
but the problem is that ViewModel is instantiated one more time in the child fragment.
Parent Fragment
#AndroidEntryPoint
class ParentFragment : Fragment() {
override val mViewModel: URLViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
mViewBinding = getViewBinding(inflater, container)
mViewModel.liveData.observe(this, { data ->
{
childFragmentManager.beginTransaction().apply {
replace(
mViewBinding.fragmentContainer.id,
ChildFragment(data)
)
}
commit()
} })
mViewModel.getURL("TEST", "2021-06-18", "2021-07-18", 1 , 0 , -1, false)
return mViewBinding.root
}
}
ChildFragment
#AndroidEntryPoint
class ChildFragment(val data: List<Item>) : Fragment() {
override val mViewModel: URLViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
mViewBinding = getViewBinding(inflater, container)
// mViewModel is instantiated again and some all strings properties of it is null.
return mViewBinding.root
}
}
URLViewModel
#HiltViewModel
class URLViewModel #Inject constructor(private val urlApi: URLApi): ViewModel() {
private val _urlLiveData = MutableLiveData<State<Any?>>()
val urlLiveData: LiveData<State<Any?>> = _urlLiveData
var urlName: String? = null
var beginDate: String? = null
var endDate: String? = null
var adultCount = 0
var childrenCount = 0
var airportId = 0
var isRoundTrip = false
init {
Log.e("URLViewModel", "iniialed again" )
}
#ExperimentalStdlibApi
fun getUrl(urlName: String, beginDate: String, endDate: String, adultCount: Int, childCount: Int, airportId: Int, isRoundTrip: Boolean){
Log.e("XXXXXX", "getUrl: called with url of " + urlName )
this.urlName = urlName
this.beginDate = beginDate
this.endDate = endDate
this.adultCount = adultCount
this.childrenCount = childCount
this.airportId = airportId
this.isRoundTrip = isRoundTrip
val mutableLiveData = MutableLiveData<State<Any?>>()
mutableLiveData.value = State.loading()
viewModelScope.launch {
val res = urlApi.getURL(urlName,beginDate,endDate,adultCount,childCount,airportId,isRoundTrip)
Log.e("URLVIewModel", "getUrl: response received" )
_urlLiveData.value = res
}
}
}
when I wanna access some properties like beginDate, they are null, because the ViewModel is instantiated again,

viewModels() delegation create view model against the same instance i.e Fragment's instance in your case. What you need to do is to create a shared View model .
There is helper delegate available for it with ktx libraries.
add the ktx dependency which you already have i guess from here.
implementation "androidx.fragment:fragment-ktx:1.3.4"
And create view model with
private val viewModel by activityViewModels<UrlViewModel>()

You do not have to use activity shared view model. Simply request view model from parent fragment in ChildFragment.
private val viewModel by viewModels<UrlViewModel>(ownerProducer = { requireParentFragment() })

You are trying to use share viewmodel. Try to following code for reference.
#AndroidEntryPoint
class ParentFragment : Fragment() {
private lateinit var viewModel: URLViewModel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(requireActivity()).get(URLViewModel::class.java)
}
}
#AndroidEntryPoint
class ChildFragment : Fragment() {
private lateinit var viewModel: URLViewModel
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel = ViewModelProvider(requireActivity()).get(URLViewModel::class.java)
}
}

Values are not added in MutableLiveData<MutableList<String>>()

I am using a fragment and viewmodel where the list values are not updated in the viemodel when the function is called from my fragment.
This is in my fragment
class SettingsFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val binding = FragmentSettingsBinding.inflate(inflater)
val application = requireNotNull(this.activity).application
val dataSource = UserInfoDatabase.getInstance(application).userInfoDao
val viewModelFactory = SettingsViewModelFactory(dataSource, application)
val settingsViewModel = ViewModelProvider(this, viewModelFactory).get(SettingsViewModel::class.java)
binding.settingsViewModel = settingsViewModel
binding.lifecycleOwner = this
settingsViewModel.addValueToList("hello")
}
}
This is from my ViewModel
class SettingsViewModel(val database: UserInfoDatabaseDao, application: Application): AndroidViewModel(application){
private val _sectionList = MutableLiveData<MutableList<String>>()
val sectionList: MutableLiveData<MutableList<String>>
get() = _sectionList
fun addValueToList(listValue: String){
_sectionList.value?.add(listValue)
}
}
When I try to print a toast message as _sectionList.value.toString() from my viewModel after trying to add values to the list, it shows null.
Thanks in advance for the help..

It's because you have not initialized the MutableList<>().
class SettingsViewModel(val database: UserInfoDatabaseDao, application: Application): AndroidViewModel(application){
private val _sectionList = MutableLiveData<MutableList<String>>()
val sectionList: MutableLiveData<MutableList<String>>
get() = _sectionList
fun addValueToList(listValue: String){
// In the following line: _sectionList.value is still null, so this will
// never call the add
_sectionList.value?.add(listValue)
}
}
If you initialize with:
init {
_sectionList.value = mutableListOf<String>()
}
it should work hopefully.