ListAdapter with paging support

gistfile1.txt

class CarNewsAdapter(
        private val context: Context,
        private val dateTimeFormatter: DateTimeFormatter,
        private val recycler: RecyclerView,
        private val callback: Callback,
        private val onLoadMoreListener: OnLoadMoreListener) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    private val imageRoundedTransformation = RoundedCornersTransformation(context, 8, 0)
    private var isLoading = false
    private var visibleThreshold = THRESHOLD_LIMIT
    private var lastVisibleItem = 0
    private var totalItemCount = 0
    private var layoutManager = recycler.layoutManager as LinearLayoutManager
    private var scrollListener: RecyclerView.OnScrollListener = object : RecyclerView.OnScrollListener() {
        override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            super.onScrolled(recyclerView, dx, dy)
            totalItemCount = layoutManager.itemCount
            lastVisibleItem = layoutManager.findLastVisibleItemPosition()
            if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
                onLoadMoreListener.onLoadMore()
                isLoading = true
            }
        }
    }

    init {
        recycler.addOnScrollListener(scrollListener)
    }

    interface Callback {
        fun onItemClick(item: CarNewsViewItem)
    }

    class ItemViewHolder(view: View, adapter: CarNewsAdapter) : RecyclerView.ViewHolder(view) {
        init {
            view.setOnClickListener {
                adapter.callback.onItemClick(it?.tag as CarNewsViewItem)
            }
        }
    }

    class ProgressViewHolder(view: View) : RecyclerView.ViewHolder(view)

    private val items: MutableList<CarNewsViewItem?> = arrayListOf()

    fun clear() {
        items.clear()
    }

    fun addItems(items: List<CarNewsViewItem?>) {
        val ind = itemCount
        if (ind > 0) {
            removeItem(ind - 1)
            notifyItemRemoved(ind - 1)
        }
        if (items.isNotEmpty()) {
            this.items.addAll(items)
            notifyItemRangeInserted(itemCount, items.size)
            addProgressItem()
            notifyItemInserted(itemCount)
        } else {
            recycler.removeOnScrollListener(scrollListener)
        }
        setLoaded()
    }

    fun addProgressItem() {
        this.items.add(null)
    }

    fun getItem(position: Int): CarNewsViewItem? {
        if (position < items.size) {
            return items[position]
        }
        return null
    }

    fun removeItem(position: Int) {
        if (position < items.size) {
            items.removeAt(position)
        }
    }

    private fun setLoaded() {
        isLoading = false
    }

    override fun getItemViewType(position: Int): Int {
        return if (items[position] != null) VIEW_TYPE_ITEM else VIEW_TYPE_LOADING
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder? {
        if (viewType == VIEW_TYPE_ITEM) {
            val view = LayoutInflater.from(context).inflate(R.layout.list_item_car_news, parent, false)
            return ItemViewHolder(view, this)
        } else if (viewType == VIEW_TYPE_LOADING) {
            val view = LayoutInflater.from(context).inflate(R.layout.list_item_progress, parent, false)
            return ProgressViewHolder(view)
        }

        return null
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        when (holder) {
            is ItemViewHolder -> {
                val item = items[position]
                with(holder.itemView) {
                    item?.let {
                        tag = it
                        title.text = it.title
                        date.text = dateTimeFormatter.formatDate(it.date)
                        Glide.with(context)
                                .load(it.image)
                                .fitCenter()
                                .centerCrop()
                                .bitmapTransform(imageRoundedTransformation)
                                .into(image)
                    }
                }
            }

            is ProgressViewHolder -> {
                holder.itemView.progress.isIndeterminate = true
            }
        }
    }

    override fun getItemCount(): Int {
        return items.size
    }

}

private const val VIEW_TYPE_ITEM = 0
private const val VIEW_TYPE_LOADING = 1
private const val THRESHOLD_LIMIT = 5