Paging UICollectionView by cells, not screen

Question

I have UICollectionView with horizontal scrolling and there are always 2 cells side-by-side per the entire screen. I need the scrolling to stop at the begining

Answer 1

modify Romulo BM answer for velocity listening

func scrollViewWillEndDragging(
    _ scrollView: UIScrollView,
    withVelocity velocity: CGPoint,
    targetContentOffset: UnsafeMutablePointer
) {
    targetContentOffset.pointee = scrollView.contentOffset
    var indexes = collection.indexPathsForVisibleItems
    indexes.sort()
    var index = indexes.first!
    if velocity.x > 0 {
       index.row += 1
    } else if velocity.x == 0 {
        let cell = self.collection.cellForItem(at: index)!
        let position = self.collection.contentOffset.x - cell.frame.origin.x
        if position > cell.frame.size.width / 2 {
           index.row += 1
        }
    }

    self.collection.scrollToItem(at: index, at: .centeredHorizontally, animated: true )
}