This is a sample of a Centered CollectionView Flow Layout

CollectionViewCenterLayout.swift

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    ...
    var rows = [CollectionViewRow]()
    var currentRowY: CGFloat = -1

    for attribute in attributes {
        if currentRowY != attribute.frame.origin.y {
            currentRowY = attribute.frame.origin.y
            rows.append(CollectionViewRow(spacing: 10))
        }
        rows.last?.add(attribute: attribute)
    }
}