How to add more list of data without clearing the previous in Recycler View Adapter in kotlin?

Question

I'm trying to make a recycler view that load more data as the user scroll down without deleting the previous cell. example:(Instagram, twitter...)

when I scroll down the new data is fetched in all the recycler-view cells the previous and the new cells.

so if I have 10cells, then I scroll down, it gets another new 10 however now all 20 are the same, and the first 10 are substituted.

The Main fragment

        photosList.layoutManager = mLayoutManager

        viewModel.refresh()
        photosList.apply {
            layoutManager = LinearLayoutManager(context)
            adapter = photosAdapter
        }

        observeViewModel()

        photosList.addOnScrollListener(object : RecyclerView.OnScrollListener() {
            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                if (dy > 0) { //check for scroll down
                    //visibleItemCount = mLayoutManager.childCount
                    var layoutManager = photosList.layoutManager as LinearLayoutManager
                    visibleItemCount =
                        layoutManager.findLastVisibleItemPosition() - layoutManager.findFirstVisibleItemPosition() + 1
                    totalItemCount = layoutManager.itemCount
                    pastVisibleItems = layoutManager.findFirstVisibleItemPosition()
                    if (loading) {
                        if (visibleItemCount + pastVisibleItems >= totalItemCount) {
                            loading = false

                            // Fetch new data
                            viewModel.fetchMorePhotos()
                            observeViewModelGetMore()

                            loading = true
                        }
                    }
                }
            }
        })

The ViewModel

fun fetchMorePhotos() {
        pageNumber += 1
        fetchPhotos()
    }

    private fun fetchPhotos() {
        loading.value = true
        //loading2.value = true
        disposable.add(
            PhotosService.getPhotos(pageNumber)
                .subscribeOn(Schedulers.newThread())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWith(object : DisposableSingleObserver<List<PhotoData>>() {
                    override fun onSuccess(value: List<PhotoData>?) {
                        Photos.value = value!!
                        PhotoLoadError.value = false
                        loading.value = false
                        //loading2.value = false
                    }

                    override fun onError(e: Throwable?) {
                        PhotoLoadError.value = true
                        loading.value = false
                        //loading2.value = false
                    }

                })
        )
    }

The Adapter

class PhotoListAdapter(
    var photos: ArrayList<PhotoData>,
    private var click_listener: OnPhotoItemClickListner
) :
    RecyclerView.Adapter<PhotoListAdapter.PhotoViewHolder>() {
    fun updatePhotos(newPhotos: List<PhotoData>) {
        photos.clear()
        photos.addAll(newPhotos)
        notifyDataSetChanged()
    }

    fun getMorePhotos(newPhotos: List<PhotoData>) {
        val position: Int = photos.size + 1
        photos.addAll(newPhotos)
        notifyItemChanged(position,newPhotos)
    }

Answer 1

Infinite scrolling is a complicated topic that I wouldn't try to solve yourself. You'll want to use the Android Paging library:

https://proandroiddev.com/infinite-scrolling-with-android-paging-library-and-flow-api-e017f47517d6