https://ferrand-d.medium.com/paging-image-gallery-with-recyclerview-f059d035b7e7

PagingImageGallery_boundsOffsetDecoration.kt

class BoundsOffsetDecoration : ItemDecoration() {
    override fun getItemOffsets(outRect: Rect,
                                view: View,
                                parent: RecyclerView,
                                state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)

        val itemPosition = parent.getChildAdapterPosition(view)

        // It is crucial to refer to layoutParams.width
        // (view.width is 0 at this time)!
        val itemWidth = view.layoutParams.width
        val offset = (parent.width - itemWidth) / 2

        if (itemPosition == 0) {
            outRect.left = offset
        } else if (itemPosition == state.itemCount - 1) {
            outRect.right = offset
        }
    }
}