[FIXED] Recycler view not update itself

Issue

I have a problem with recycler view. In my previous app, when i get the list for recycler view adapter from database and observe it in my fragment, i used the notifyDataSetChanged() and when i tried to delete a item , view updated successfully. But in this app this does not work and i don't understand why. When i click the delete button the item deleted in database successfully but i can't see it immediatly. When i go to any other fragment and back to this Favourites fragment i see the items deleted. I tried all the options in stackoverflow but still i can't fix it. My Adapter:

class FavouritesAdapter(owner: ViewModelStoreOwner, val favouritesList : ArrayList<Vocabulary>) : RecyclerView.Adapter<FavouritesAdapter.FavouritesViewHolder>() {
    val viewModel = ViewModelProvider(owner).get(FavouritesViewModel::class.java)

    class FavouritesViewHolder(val binding: FavouritesItemRowBinding) : RecyclerView.ViewHolder(binding.root)


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FavouritesViewHolder {
        return FavouritesViewHolder(FavouritesItemRowBinding.inflate(LayoutInflater.from(parent.context), parent, false))

    }

    override fun onBindViewHolder(holder: FavouritesViewHolder, position: Int) {
        holder.binding.englishWordTV.text = favouritesList[position].word
        holder.binding.turkishWordTV.text = favouritesList[position].translation

        holder.binding.deleteButtonRV.setOnClickListener {
            viewModel.deleteVocabulary(favouritesList[position])
            notifyDataSetChanged()
        }

    }

    override fun getItemCount(): Int {
        return favouritesList.size
    }
    fun updateList(myList : List<Vocabulary>) {
        favouritesList.clear()
        favouritesList.addAll(myList)
        notifyDataSetChanged()

    }


} 

My problem is in delete button in my recycler row;

holder.binding.deleteButtonRV.setOnClickListener {
            viewModel.deleteVocabulary(favouritesList[position])
            notifyDataSetChanged()
        }

And here is my fragment ;

class FavouritesFragment : Fragment() {
    private var _binding: FragmentFavouritesBinding? = null
    private val binding get() = _binding!!
    private lateinit var favouritesAdapter : FavouritesAdapter
    private lateinit var viewModel : FavouritesViewModel


    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = FragmentFavouritesBinding.inflate(inflater, container, false)
        return binding.root


    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        viewModel = ViewModelProvider(this).get(FavouritesViewModel::class.java)
        favouritesAdapter = FavouritesAdapter(this, arrayListOf())
        viewModel.getAllVocabulariesFromDB()

        prepareRecyclerView()
        observeFavouritesLiveData()
    }


    fun prepareRecyclerView(){
        binding.favouritesRecyclerView.apply {
            layoutManager = LinearLayoutManager(context)
            adapter = favouritesAdapter
        }
    }

    fun observeFavouritesLiveData(){
        viewModel.favouritesListLiveData.observe(viewLifecycleOwner, Observer {

            it?.let {
                favouritesAdapter.updateList(it)
            }
        })
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null


    }
    
}

Solution

i tried to use the path "button click -> UI sends delete event to VM -> VM updates data -> observer sees new data -> observer calls update with new data" as @cactuctictacs mentioned. I added this lines to my adapter,

lateinit var onDeleteItemClick : ((Vocabulary) -> Unit)

holder.binding.deleteButtonRV.setOnClickListener {
        onDeleteItemClick.invoke(favouritesList[position])
        notifyItemRemoved(position)
  }

and added to my fragment,

fun deleteButtonClicked(){
        favouritesAdapter.onDeleteItemClick = {
            viewModel.deleteVocabulary(it)
            viewModel.getAllVocabulariesFromDB()

            observeFavouritesLiveData()
            favouritesAdapter.notifyDataSetChanged()
        }
    }

I hope this is the proper way to do this.

Answered By - Ugur
Answer Checked By - Marie Seifert (JavaFixing Admin)