Add Infinite Scroll to RecyclerView

InfiniteScrollExtensions.kt

import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.StaggeredGridLayoutManager

fun RecyclerView.attachInfiniteScroll(onLoadMoreListener: OnLoadMoreListener) {
    if (layoutManager != null)
        setInfiniteScrollGrid(this, layoutManager!!, onLoadMoreListener)
    else throw RuntimeException("Layout Manager is Not Set")
}

/**
 * this function get scrolling control of [.recyclerView] and whenever
 * user reached list ends, [.onLoadMoreListener] will be called
 */
private fun setInfiniteScrollGrid(
    recyclerView: RecyclerView,
    layoutManager: RecyclerView.LayoutManager,
    onLoadMoreListener: OnLoadMoreListener
) {
    var totalItemCount = 0
    var previousItemCount = 0
    val threshold = 4
    var lastVisibleItem = 0
    var isLoading = false
    recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
        override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
            totalItemCount = layoutManager.itemCount
            if (previousItemCount > totalItemCount) {
                previousItemCount = totalItemCount - threshold
            }
            when (layoutManager) {
                is GridLayoutManager -> {
                    lastVisibleItem = layoutManager.findLastVisibleItemPosition()
                }
                is LinearLayoutManager -> {
                    lastVisibleItem = layoutManager.findLastVisibleItemPosition()
                }
                is StaggeredGridLayoutManager -> {
                    val spanCount = layoutManager.spanCount
                    val ids = IntArray(spanCount)
                    layoutManager.findLastVisibleItemPositions(ids)
                    var max = ids[0]
                    for (i in 1 until ids.size) {
                        if (ids[1] > max) {
                            max = ids[1]
                        }
                    }
                    lastVisibleItem = max
                }
            }
            if (totalItemCount > threshold) {
                if (previousItemCount <= totalItemCount && isLoading) {
                    isLoading = false
                }
                if (!isLoading && lastVisibleItem > totalItemCount - threshold && totalItemCount > previousItemCount) {
                    onLoadMoreListener.onLoadMore()
                    isLoading = true
                    previousItemCount = totalItemCount
                }
            }
            super.onScrolled(recyclerView, dx, dy)
        }
    })
}

interface OnLoadMoreListener {
    fun onLoadMore()
}