how to remove previous result list immediately when updating recycler view?

Question

here is the short video of my problem: https://drive.google.com/file/d/108Tk9rmJtF3Ir7Nj9hheW2JkvlqXggcj/view

so, I have a vertical recycler view that can be refreshed when the tab layout is tapped.

If I tap the first index of the tab, it will fetch some data from the server and populate the adapter and recycler view. but if I tap the second index, the data from server is actually empty.

here is the problem...

as you can see from the short video above. when I tap the second tab (from previously in the first tab), it still shows the list from the first tab appears for a second before eventually show an empty recycler view.

I want to make after the loading the data from server, that previous result will not show, and it should immediately show the result as per the tab selected.

I am using ListAdapter and using submitList() to update the data

here is the adapter I use:

class GeneralEventRecyclerViewAdapter(val mContext: Context): ListAdapter<Event, RecyclerView.ViewHolder>(DIFF_CALLBACK) {

    lateinit var mOnEventKMListener : OnEventKMListener

    fun setOnItemClickListener(listener: OnEventKMListener) {
        mOnEventKMListener = listener
    }


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.item_general_event, parent, false)
        return GeneralEventViewHolder(itemView, mOnEventKMListener)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {

        val currentEvent = getItem(position)
        val generalEventViewHolder = holder as GeneralEventViewHolder

        Glide.with(mContext).load(currentEvent.thumbnailDownloadPath)
            .apply(RequestOptions.bitmapTransform(BlurTransformation(25, 3)))
            .into(generalEventViewHolder.blurThumbnailImageView)

        Glide.with(mContext).load(currentEvent.thumbnailDownloadPath).into(generalEventViewHolder.thumbnailImageView)


        generalEventViewHolder.eventNameTextView.text = currentEvent.title
        generalEventViewHolder.eventVenueTextView.text = currentEvent.venue
        generalEventViewHolder.eventDateTimeTextView.text = DateTimeService.changeDateToString("EEEE, d MMMM. HH:mm zzz",currentEvent.dateTimeStart)

    }


    companion object {

        private val DIFF_CALLBACK = object : DiffUtil.ItemCallback<Event>() {
            override fun areItemsTheSame(oldItem: Event, newItem: Event): Boolean {
                return oldItem.eventID == newItem.eventID
            }

            override fun areContentsTheSame(oldItem: Event, newItem: Event): Boolean {
                return oldItem == newItem
            }


        }
    }


}

and here is the simplified my fragment class:

class SearchResultFragment : Fragment() {

    lateinit var titleTextView: TextView
    lateinit var progressBar : ProgressBar
    lateinit var fragmentView : View
    lateinit var tabLayout : TabLayout
    lateinit var recyclerView : RecyclerView

    lateinit var mContext : Context
    lateinit var mActivity : FragmentActivity
    lateinit var eventAdapter : GeneralEventRecyclerViewAdapter

    private var eventList = ArrayList<Event>()
    private var selectedEventType = EventType.kajianUmum
    private var selectedCity = City.defaultCityName
    private var selectedTime = EventTimeUserSelection.Weekend
    lateinit var userData : User

    private var startingDate = Date()
    private var endingDate = Date()

    override fun onAttach(context: Context) {
        super.onAttach(context)

        mContext = context
        activity?.let { mActivity = it }

    }



    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        fragmentView = inflater.inflate(R.layout.fragment_search_result, container, false)

        setUpSafeArg()
        setUpViewsDeclaration()
        setUpListeners()
        updateUI()
        setHasOptionsMenu(true)

        initRecyclerView()
        searchEvents()




        return fragmentView
    }



    private fun setUpViewsDeclaration() {
        titleTextView = mActivity.findViewById(R.id.destination_label_text_view)
        progressBar = mActivity.progressBar_main_activity
        recyclerView = fragmentView.findViewById(R.id.recyclerView_search_result)
        tabLayout = fragmentView.findViewById(R.id.tabLayout_time_search_result)

    }



    private fun setUpListeners() {

        tabLayout.addOnTabSelectedListener(object: TabLayout.OnTabSelectedListener {

            override fun onTabSelected(tab: TabLayout.Tab?) {

                selectedTime = when(tab?.position ?: 0) {
                    0 -> EventTimeUserSelection.All
                    1 -> EventTimeUserSelection.Today
                    2 -> EventTimeUserSelection.Tomorrow
                    3 -> EventTimeUserSelection.Weekend
                    4 -> EventTimeUserSelection.ThisWeek
                    5 -> EventTimeUserSelection.NextWeek
                    else -> EventTimeUserSelection.All
                }

                searchEvents()


            }

            override fun onTabReselected(tab: TabLayout.Tab?) {

            }

            override fun onTabUnselected(tab: TabLayout.Tab?) {

            }


        })

    }


    private fun initRecyclerView() {

        eventAdapter = GeneralEventRecyclerViewAdapter(mContext)
        val layoutManager = LinearLayoutManager(mContext, RecyclerView.VERTICAL,false)
        recyclerView.adapter = eventAdapter
        recyclerView.layoutManager = layoutManager


        eventAdapter.setOnItemClickListener(object: OnEventKMListener {

            override fun eventKMClicked(position: Int) {
                val selectedEvent = eventList[position]
                val eventDetailDestination = SearchResultFragmentDirections.actionGlobalDestinationEventDetail(selectedEvent)
                Navigation.findNavController(fragmentView).navigate(eventDetailDestination)
            }

        })




    }

    private fun searchEvents() {

        setStartingAndEndingDateForSearching()
        progressBar.visibility = View.VISIBLE
        recyclerView.visibility = View.GONE


        FirestoreKMClient.getFreeEvents(startingDate,endingDate,selectedCity,selectedEventType.getEventTypeInString(),10) { errorMessage, events ->


            errorMessage?.let {
                mActivity.toast(it)
            } ?: run {

                val theEvents = events ?: ArrayList()
                eventList = theEvents
                eventAdapter.submitList(eventList)
            }

            progressBar.visibility = View.GONE
            recyclerView.visibility = View.VISIBLE


        }


    }


}

Java is ok

Answer 1

You should have to clear the list on a time of calling your data from database.

Try setting up empty list before call of new data i.e. In searchEvents() function below this line recyclerView.visibility = View.GONE.

recyclerView.visibility = View.GONE
eventList = arrayOf< Event>()
eventAdapter.submitList(eventList)

Answer 2

I'm not good in kotlin but the my logic might work;

upon reading your code;

i guess you can try to set your adapter into null first so that it will clear all previous data that is been fetch on your first tab.

eventAdapter.submitList(null)

you can try to put it here :

 private fun searchEvents() {

        setStartingAndEndingDateForSearching()
        progressBar.visibility = View.VISIBLE
        recyclerView.visibility = View.GONE
        eventAdapter.submitList(null)