Adds even spacing to a RecyclerView accepting a custom span count

SpacesItemDecoration.kt

class SpacesItemDecoration(private val space: Int, private val span: Int) : RecyclerView.ItemDecoration() {
  override fun getItemOffsets(outRect: Rect, view: View, parent: RecyclerView, state: RecyclerView.State) {
    val position = parent.getChildAdapterPosition(view)
    val lastPosition = parent.adapter.itemCount - 1

    val bottomRow = (lastPosition - position) < span
    val rightColumn = (position % span) == (span - 1)

    /**
     * |A----B----C|
     * |           |
     * |           |
     * D     I     E
     * |           |
     * |           |
     * |F----G----H|
     */

    // All get top and left
    outRect.top = space
    outRect.left = space

    // C & E & H
    if (rightColumn) {
      outRect.right = space
    }

    // F & G & H
    if (bottomRow) {
      outRect.bottom = space
    }
  }
}

SpacesItemDecorationHowTo.kt

val spaceInPixels = resources.getDimensionPixelSize(R.dimen.cell_space)
val numberOfColumns = 2
val spaceDecoration = SpacesItemDecoration(spaceInPixels, numberOfColumns)
recyclerView.addItemDecoration(spaceDecoration)