ReturnToTopDemoLayoutManager.kt

recyclerView.layoutManager = object :
                LinearLayoutManager(context, LinearLayoutManager.VERTICAL, false) {
            override fun onLayoutCompleted(state: RecyclerView.State?) {
                super.onLayoutCompleted(state)
                if (showReturnToTopButton
                        && (findLastVisibleItemPosition()
                                - findFirstVisibleItemPosition()
                                + 1
                                < adapter.itemCount)) {
                    buttonReturnToTop.visibility = View.VISIBLE
                    showReturnToTopButton = false
                }
            }
        }