Scroll example

private fun onSubSharesScrolled() {
    val subSharesLm = subSharesRecyclerView.layoutManager as LinearLayoutManager
    val variantsLm = variantsRecyclerView.layoutManager as LinearLayoutManager
    val first = subSharesLm.findFirstVisibleItemPosition()
    val last = subSharesLm.findLastVisibleItemPosition()
    if (first < 0 || last < 0) {
        // When the list is empty, we get -1 for the positions.
        return
    }

    val firstId = verticalVariantIndexes[first]
    val lastId = verticalVariantIndexes[last]
    val range = verticalVariantIndexes.values.indexOf(firstId)..verticalVariantIndexes.values.indexOf(lastId)
    if (range != cachedRange) {
        cachedRange = highlightRange
        val selectedPosition = horizontalVariantIndexes[firstId]
        smoothScroller.targetPosition = selectedPosition ?: return
        variantsLm.startSmoothScroll(smoothScroller)
    }
}