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My recyclerview resets when I add or delete an item from a Table (with Room) in Kotlin

First of all, I am Spanish so my english is not good.
I have an app with Kotlin and room, and it has a Recyclerview.
I have 3 tables: coaster, user and favorite.
The user can add coasters to favorite, and this is done succesfully.
The problem that I have is that when the user clicks on the button to add or delete from favorites, the recyclerview resets, it displays again. So it scrolls to the top of the Screen, and also some odd spaces appears after the element.
I also have a function to search, and it happens the same: spaces appears after each element when I am searching.
I have tried everything: notifyItemChanged,
notifyDataSetChanged... it doesnt work! I also tried removing the observer once from the recyclerview...
My main activity:
class CoasterFragment : Fragment() {
lateinit var coasterListener: CoasterListener
lateinit var usuarioCoaster: List\<UsuarioCoaster\>
private lateinit var searchView: SearchView
private lateinit var cAdapter: CoasterRecyclerViewAdapter
private var \_binding: FragmentCoasterBinding? = null
private val binding get() = \_binding!!
private val viewModel: CoastersViewModel by viewModels()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentCoasterBinding.inflate(inflater, container, false)
val root: View = binding.root
/* val livedata = viewModel.coasters()
livedata.observe(viewLifecycleOwner,object: Observer <List<CoasterFavorito>> {
override fun onChanged(it: List<CoasterFavorito>) {
createRecyclerView(it)
livedata.removeObserver(this)
}
})*/
viewModel.coasters().observe(viewLifecycleOwner){createRecyclerView(it)}
coasterListener = CoasterListenerImpl(requireContext(), viewModel)
searchView = binding.search
searchView.clearFocus()
searchView.setOnQueryTextListener(object: SearchView.OnQueryTextListener{
override fun onQueryTextSubmit(query: String?): Boolean {
if(query != null){
searchDatabase(query)
}
return true
}
override fun onQueryTextChange(query: String?): Boolean {
if(query != null){
searchDatabase(query)
}
return true
}
})
return root
}
fun createRecyclerView(coasters: List<CoasterFavorito>) {
cAdapter =
CoasterRecyclerViewAdapter(
coasters as MutableList<CoasterFavorito>,
coasterListener,
requireContext()
)
val recyclerView = binding.recyclerCoaster
recyclerView.apply {
layoutManager = LinearLayoutManager(context, RecyclerView.VERTICAL, false)
adapter = cAdapter
addItemDecoration(DividerItemDecoration(context, RecyclerView.VERTICAL))
cAdapter.notifyDataSetChanged()
}
}
fun searchDatabase(query: String) {
val searchQuery = "%$query%"
viewModel.searchDatabase(searchQuery).observe(viewLifecycleOwner) { createRecyclerView(it)
}
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
}
my adapter:
class CoasterRecyclerViewAdapter(val coasters: List<CoasterFavorito>, val listener: CoasterListener,
val context: Context, ) : RecyclerView.Adapter<CoasterRecyclerViewAdapter.ViewHolder>(){
class ViewHolder private constructor(val binding: CoasterItemBinding, private val listener: CoasterListener,
private val context: Context): RecyclerView.ViewHolder(binding.root){
fun relleno(data: CoasterFavorito){
binding.nombre.text = data.coaster.nombre
binding.parque.text = data.coaster.parque
binding.ciudad.text = data.coaster.ciudad
binding.provincia.text = data.coaster.provincia
binding.comunidad.text = data.coaster.comunidadAutonoma
Glide
.with(context)
.load(data.coaster.imagen)
.centerCrop()
.into(binding.imagen)
binding.check.isChecked = data.favorito
binding.check.setOnClickListener{
if (data.favorito) {
listener.delFavorito(data.coaster.id)
binding.check.isChecked = false
} else {
listener.addFavorito(data.coaster.id)
binding.check.isChecked = true
}
}
}
companion object{
fun crearViewHolder(parent: ViewGroup, listener: CoasterListener, adapter: CoasterRecyclerViewAdapter, context: Context):ViewHolder{
val layoutInflater = LayoutInflater.from(parent.context)
val binding = CoasterItemBinding.inflate(layoutInflater, parent, false)
return ViewHolder(binding, listener, context )
}
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int) = ViewHolder.crearViewHolder(parent, listener, this, context)
override fun onBindViewHolder(holder: ViewHolder, position: Int) = holder.relleno(coasters[position])
override fun getItemCount() = coasters.size
}
interface CoasterListener {
fun addFavorito(id: Long)
fun delFavorito(id: Long)
}
I have tried everything: notifyItemChanged,
notifyDataSetChanged... it doesnt work! I also tried removing the observer once from the recyclerview...

Your createRecyclerView function should be invoked only once in a whole lifecycle of the Fragment. You should not create any new RecyclerView.Adapter, or set a LayoutManager to the RecyclerView every time your data set changes.
Therefore the Observer used in viewModel.coasters.observe() should only submit a new List to the existing Adapter and call .notifyDataSetChanged(), or other notifying functions.

How can I display firebase data in a fragment with recyclerview? Kotlin Android Studio

hello I have an activity that has a navigation bar and fragments inside, in one of my fragments I save data in firebase, I want to get those data and display it in other fragment with recycler view. I watched a tutorial on youtube to do it cuz my teacher didn't teach us anything, the issue is the fragment that was supposed the display the data shows nothing, it's blank but I didn't understand why cuz I'm really new to this, if someone can take a look at my code and help me I would really appreciate it
This is my data class
data class Event(var eventName: String, var eventTime:String?=null)
This is ViewModel
class EventViewModel :ViewModel() {
private val repository : EventRepository
private val _allEvents = MutableLiveData<List<Event>>()
val allEvents : LiveData<List<Event>> = _allEvents
init {
repository= EventRepository().getInstance()
repository.loadEvents(_allEvents)
}
}
This is Repository
class EventRepository {
private val databaseReference: DatabaseReference= FirebaseDatabase.getInstance().getReference("PetEvents")
#Volatile private var INSTANCE : EventRepository ?=null
fun getInstance() : EventRepository{
return INSTANCE ?: synchronized(this) {
val instance = EventRepository()
INSTANCE=instance
instance
}
}
fun loadEvents(eventList : MutableLiveData<List<Event>>){
databaseReference.addValueEventListener(object:ValueEventListener{
override fun onDataChange(snapshot: DataSnapshot) {
try {
val _eventList : List<Event> = snapshot.children.map { dataSnapshot ->
dataSnapshot.getValue(Event::class.java)!!
}
eventList.postValue(_eventList)
}
catch (e: Exception){
}
}
override fun onCancelled(error: DatabaseError) {
TODO("Not yet implemented")
}
})
}
}
This is Adapter
class EventAdapter : RecyclerView.Adapter<EventAdapter.MyViewHolder>() {
private var eventList =ArrayList<Event>()
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val itemView = LayoutInflater.from(parent.context).inflate(
R.layout.event_item_cell,
parent, false
)
return MyViewHolder(itemView)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
val currentItem = eventList[position]
holder.eventName.text =currentItem.eventName
holder.eventTime.text =currentItem.eventTime
}
override fun getItemCount(): Int {
return eventList.size
}
fun updateEventList(eventList: List<Event>){
this.eventList.clear()
this.eventList.addAll(eventList)
notifyDataSetChanged()
}
class MyViewHolder(itemView: View): RecyclerView.ViewHolder(itemView){
val eventName :TextView = itemView.findViewById(R.id.txEventName)
val eventTime :TextView = itemView.findViewById(R.id.txEventTime)
}
}
And this is the fragment I wish to display the data
private lateinit var viewModel : EventViewModel
private lateinit var eventRecyclerView: RecyclerView
lateinit var adapter: EventAdapter
class MainFragment : Fragment() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_main, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
eventRecyclerView=view.findViewById(R.id.recyclerView)
eventRecyclerView.layoutManager= LinearLayoutManager(context)
eventRecyclerView.setHasFixedSize(true)
adapter = EventAdapter()
eventRecyclerView.adapter= adapter
viewModel = ViewModelProvider(this).get(EventViewModel::class.java)
viewModel.allEvents.observe(viewLifecycleOwner, Observer {
adapter.updateEventList(it)
})
}
}
In my fragment xml I put a recycler view, there's no issue about that
And my item cell is a cardview idk if it has anything to with the problem I'm getting tho

LiveData observing not working after Room database updates

My app contains a Room db of cocktail recipes that it downloads via a Retrofit api call, all of that is working well. To focus in on where my problem lies, my use case is a user adding a cocktail to a list. This is done via a DialogFragment and here the DialogFragment displays, the transaction executes, the DialogFragment goes away and the Room db is updated. The cocktail fragment does not get the update though - if you navigate away and back, the update is visible so I know the transaction worked as expected. One thing I just noticed is if I rotate the device, the update gets picked up as well.
Here is the relevant section of my fragment:
class CocktailDetailFragment : BaseFragment<CocktailDetailViewModel, FragmentCocktailDetailBinding, CocktailDetailRepository>() {
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewModel.cocktail.observe(viewLifecycleOwner, Observer {
when(it){
is Resource.Success -> {
updateCocktail(it.value)
}
}
})
}
private fun updateCocktail(cocktail: Cocktail) {
with(binding){
detailCocktailName.text = cocktail.cocktailName
//...
//this is the piece of functionality i'm expecting the LiveData observer to execute and change the drawable
if(cocktail.numLists > 0) {
detailCocktailListImageView.setImageResource(R.drawable.list_filled)
} else {
detailCocktailListImageView.setImageResource(R.drawable.list_empty)
}
}
}
override fun getViewModel() = CocktailDetailViewModel::class.java
override fun getFragmentBinding(
inflater: LayoutInflater,
container: ViewGroup?
) = FragmentCocktailDetailBinding.inflate(inflater,container,false)
override fun getFragmentRepository(): CocktailDetailRepository {
val dao = GoodCallDatabase(requireContext()).goodCallDao()
return CocktailDetailRepository(dao)
}
}
BaseFragment:
abstract class BaseFragment<VM: BaseViewModel, B: ViewBinding, R: BaseRepository>: Fragment() {
protected lateinit var userPreferences: UserPreferences
protected lateinit var binding: B
protected lateinit var viewModel: VM
protected val remoteDataSource = RemoteDataSource()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
userPreferences = UserPreferences(requireContext())
binding = getFragmentBinding(inflater, container)
val factory = ViewModelFactory(getFragmentRepository())
viewModel = ViewModelProvider(this, factory).get(getViewModel())
return binding.root
}
abstract fun getViewModel() : Class<VM>
abstract fun getFragmentBinding(inflater: LayoutInflater, container: ViewGroup?): B
abstract fun getFragmentRepository(): R
}
ViewModelFactory:
class ViewModelFactory(
private val repository: BaseRepository
): ViewModelProvider.NewInstanceFactory() {
#Suppress("UNCHECKED_CAST")
override fun <T : ViewModel?> create(modelClass: Class<T>): T {
return when{
modelClass.isAssignableFrom(CocktailDetailViewModel::class.java) -> CocktailDetailViewModel(repository as CocktailDetailRepository) as T
else -> throw IllegalArgumentException("ViewModel class not found")
}
}
}
ViewModel:
class CocktailDetailViewModel(
private val repository: CocktailDetailRepository
): BaseViewModel(repository) {
private val _cocktail: MutableLiveData<Resource<Cocktail>> = MutableLiveData()
val cocktail: LiveData<Resource<Cocktail>>
get() = _cocktail
fun getCocktailByCocktailId(cocktailId: Int) = viewModelScope.launch {
_cocktail.value = Resource.Loading
_cocktail.value = repository.getCocktail(cocktailId)
}
}
Repository:
class CocktailDetailRepository(
private val dao: GoodCallDao
):BaseRepository(dao) {
suspend fun getCocktail(cocktailId: Int) = safeApiCall {
dao.getCocktail(cocktailId)
}
}
Safe Api Call (I use this so db/api calls run on IO):
interface SafeApiCall {
suspend fun <T> safeApiCall(
apiCall: suspend () -> T
): Resource<T> {
return withContext(Dispatchers.IO) {
try {
Resource.Success(apiCall.invoke())
} catch (throwable: Throwable) {
when (throwable) {
is HttpException -> {
Resource.Failure(false, throwable.code(), throwable.response()?.errorBody())
}
else -> {
Resource.Failure(true, null, null)
}
}
}
}
}
}
Resource:
sealed class Resource<out T> {
data class Success<out T>(val value: T) : Resource<T>()
data class Failure(
val isNetworkError: Boolean,
val errorCode: Int?,
val errorBody: ResponseBody?
): Resource<Nothing>()
object Loading: Resource<Nothing>()
}
Dao:
#Query("SELECT * FROM cocktail c WHERE c.cocktail_id = :cocktailId")
suspend fun getCocktail(cocktailId: Int): Cocktail
Thank you in advance for any help! Given the issue and how the app is working, I believe I have provided all the relevant parts but please advise if more of my code is required to figure this out.

Pass integer to ViewModel when using HILT

I am trying to figure out how to pass an integer from a fragment to a viewmodel while using hilt. I have ready that viewmodel factories can be used for this, I am not sure how this would be done using DI.
In the code below, I am trying to figure out how I can pass albumId to the viewModel. The albumId will be used when fetching data from an API endpoint.
Fragment
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
val view = inflater.inflate(R.layout.fragment_album_details, container, false)
val albumId = arguments?.getInt("album_id")
viewModel.songs.observe(viewLifecycleOwner) {
view.song_recyclerview.apply {
layoutManager = LinearLayoutManager(this.context)
adapter = SongAdapter(viewModel.songs)
}
}
return view
}
ViewModel
class SongViewModel #ViewModelInject constructor(
songRepo: SongRepository,
#Assisted savedStateHandle: SavedStateHandle
) : ViewModel(), LifecycleObserver {
val songs: LiveData<List<Song>> = songRepo.getSongs(1)
}
Repository
class SongRepository constructor(
private val musicService: MusicService
)
{
fun getSongs(album_id: Int): LiveData<List<Song>> {
val data = MutableLiveData<List<Song>>()
musicService.getAlbumTracks(album_id).enqueue(object : Callback<List<Song>> {
override fun onResponse(call: Call<List<Song>>, response: Response<List<Song>>) {
data.value = response.body()
}
override fun onFailure(call: Call<List<Song>>, t: Throwable) {
}
})
return data
}
}

I was finally able to figure out a solution to the problem. I added a field to the viewmodel, and a method to set a value for that field. Basically, I call viewModel.start(int) then call viewModel.songs.
ViewModel
class SongViewModel #ViewModelInject constructor(
songRepo: SongRepository,
#Assisted savedStateHandle: SavedStateHandle
) : ViewModel(), LifecycleObserver {
private val _id = MutableLiveData<Int>() // int field
private val _songs = _id.switchMap { id ->
songRepo.getSongs(id)
}
val songs: LiveData<List<Song>> = _songs
fun start(id: Int) { // method to update field
_id.value = id
}
}
Fragment
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// get data from bundle and pass to start()
arguments?.getInt(("album_id"))?.let { viewModel.start(it)}
viewModel.songs.observe(viewLifecycleOwner) {
view.song_recyclerview.apply {
layoutManager = LinearLayoutManager(this.context)
adapter = SongAdapter(viewModel.songs)
}
}
}

RecyclerView item not updated with LiveData

I have an application using databinding, livedata, room, kotlin koroutines, viewmodel, navigation component and dagger.
I have one activity, and two fragments.
ListFragment: Show in a recyclerview a list of items.
DetalFragment: Show the item detail, and can update some fields of the item with a save button.
The problem is when I update some fields from detailfragment, then the changes isn´t visibles in the listfragment, but when I scroll down and up, the changes become visible.
ListFragment:
#Inject
lateinit var viewModelFactory: ViewModelProvider.Factory
val viewModel: ListViewModel by viewModels {
viewModelFactory
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val bindings = ListFragmentBinding.inflate(inflater, container, false).apply {
viewmodel = viewModel
}
bindings.lifecycleOwner = this
adapter = ItemsAdapter()
bindings.recyclerView.adapter = adapter
viewModel.items.observe(
viewLifecycleOwner,
Observer { adapter.submitList(it)})
return bindings.root
}
ListViewModel:
var items: LiveData<PagedList<Item>> = repository.items
Repository:
val items<PagedList<Item>>
get()=itemDao.getAllItemsPaged().toLiveData(pageSize=50)
fun getItemFlow(id: String): Flow<Item> = itemDao.getItemFlow(id)
suspend fun updateItem(item: Item) {
itemDao.updateItem(item)
}
ItemDao:
#Query("SELECT * FROM item")
fun getAllItemsPaged(): DataSource.Factory<Int,Item>
#Query("SELECT * FROM itemWHERE id=:id")
fun getItemFlow(id:String):Flow<Item>
#Update
suspend fun updateItem(item:Item)
ItemFragment:
#Inject
lateinit var viewModelFactory: ViewModelProvider.Factory
val viewModel: ItemViewModel by viewModels {
viewModelFactory
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
viewModel.loadItem(args.itemId)
val bindings = ItemFragmentBinding.inflate(inflater, container, false).apply {
viewmodel = viewModel
buttonSave.setOnClickListener{viewModel. viewModelScope.launch {
viewModel.saveItem()
findNavController().navigateUp()
}}
}
bindings.lifecycleOwner = this
return bindings.root
}
ItemViewModel:
var item: LiveData<Item>? = null
fun loadItem(id: String) {
viewModelScope.launch {
item = repository.getItemFlow(id).asLiveData()
}
}
suspend fun saveItem() {
item!!.value!!.someField = "hi"
repository.updateItem(item!!.value!!)
}

The problem is in the items adapter. The adapter needs a correct implementation of the DiffUtil.ItemCallback.
In this case:
private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<Contador>() {
// The ID property identifies when items are the same.
override fun areItemsTheSame(oldItem: Contador, newItem: Contador) =
oldItem.id == newItem.id
// Check the properties that can change, or implements the equals method in Item class
override fun areContentsTheSame(
oldItem: Item, newItem: Item) = oldItem.someField == newItem.someField
}

I can confirm that DiffUtil is the way. In case of a generic approach over a RecyclerView:
ItemListDiffUtil.kt
open class ItemListDiffUtil<T>(private val oldItems: ArrayList<T>, private val newItems: ArrayList<T>) : DiffUtil.Callback(){
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
return oldItems[oldItemPosition] == newItems[newItemPosition]
}
override fun getOldListSize(): Int {
return oldItems.size
}
override fun getNewListSize(): Int {
return newItems.size
}
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
return oldItems[oldItemPosition] == newItems[newItemPosition]
}
}
YOUR_OBJECTAdapter.kt
class YOUR_OBJECTAdapter() : RecyclerView.Adapter<YOUR_OBJECTAdapter.MyViewHolder>() {
class MyViewHolder(viewItem: View) : RecyclerView.ViewHolder(viewItem) {
//your code
}
private var myDataset = ArrayList<YOUR_OBJECT>()
fun setDataset(data : ArrayList<YOUR_OBJECT>){
/*diffUtil*/
val diffCallback = ItemListDiffUtil(myDataset,data)
val diffResult = DiffUtil.calculateDiff(diffCallback)
diffResult.dispatchUpdatesTo(this)
myDataset.clear()
myDataset.addAll(data)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
val viewItem = LayoutInflater.from(parent.context).inflate(R.layout.YOUR_OBJECT, parent, false)
return MyViewHolder(viewItem)
}
override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
//your code
}
override fun getItemCount(): Int {
return myDataset.size
}
}