EndlessRecyclerViewScrollListener file for kotlin projects

EndlessRecyclerViewScrollListener.kt

/**
 * Created by Luca Nicoletti
 * © 17/10/2018
 * Copied from: https://gist.github.com/nesquena/d09dc68ff07e845cc622; added some little edits for Kotlin
 */

abstract class EndlessRecyclerViewScrollListener(private var visibleThreshold: Int = 5): RecyclerView.OnScrollListener() {
    private var currentPage = 0
    private var previousTotalItemCount = 0
    private var loading = true
    private val startingPageIndex = 0

    private var mLayoutManager: RecyclerView.LayoutManager? = null

    constructor(visibleThreshold: Int, layoutManager: LinearLayoutManager): this(visibleThreshold) {
        this.mLayoutManager = layoutManager
    }

    constructor(visibleThreshold: Int, layoutManager: GridLayoutManager): this(visibleThreshold) {
        this.mLayoutManager = layoutManager
        this.visibleThreshold = visibleThreshold * layoutManager.spanCount
    }

    constructor(visibleThreshold: Int, layoutManager: StaggeredGridLayoutManager): this(visibleThreshold) {
        this.mLayoutManager = layoutManager
        this.visibleThreshold = visibleThreshold * layoutManager.spanCount
    }

    fun getLastVisibleItem(lastVisibleItemPositions: IntArray): Int {
        var maxSize = 0
        for (i in lastVisibleItemPositions.indices) {
            if (i == 0) {
                maxSize = lastVisibleItemPositions[i]
            } else if (lastVisibleItemPositions[i] > maxSize) {
                maxSize = lastVisibleItemPositions[i]
            }
        }
        return maxSize
    }

    override fun onScrolled(view: RecyclerView, dx: Int, dy: Int) {
        var lastVisibleItemPosition = 0
        val totalItemCount = mLayoutManager?.itemCount ?: 0

        if (mLayoutManager is StaggeredGridLayoutManager) {
            val lastVisibleItemPositions = (mLayoutManager as StaggeredGridLayoutManager).findLastVisibleItemPositions(null)
            lastVisibleItemPosition = getLastVisibleItem(lastVisibleItemPositions)
        } else if (mLayoutManager is GridLayoutManager) {
            lastVisibleItemPosition = (mLayoutManager as GridLayoutManager).findLastVisibleItemPosition()
        } else if (mLayoutManager is LinearLayoutManager) {
            lastVisibleItemPosition = (mLayoutManager as LinearLayoutManager).findLastVisibleItemPosition()
        }

        if (totalItemCount < previousTotalItemCount) {
            this.currentPage = this.startingPageIndex
            this.previousTotalItemCount = totalItemCount
            if (totalItemCount == 0) {
                this.loading = true
            }
        }

        if (loading && totalItemCount > previousTotalItemCount) {
            loading = false
            previousTotalItemCount = totalItemCount
        }

        if (!loading && lastVisibleItemPosition + visibleThreshold > totalItemCount) {
            currentPage++
            onLoadMore(currentPage, totalItemCount, view)
            loading = true
        }
    }

    fun resetState() {
        this.currentPage = this.startingPageIndex
        this.previousTotalItemCount = 0
        this.loading = true
    }

    abstract fun onLoadMore(page: Int, totalItemsCount: Int, view: RecyclerView)

}