UICollectionViewFlowLayout with centered cells - ios

Question

I'm trying to implement a horizontal aligned CollectionView with centered cells and I'm using a custom UICollectionViewFlowLayout. I found several solutions with UICollectionViewDelegateFlowLayout but the delegate is not called, if you use a custom UICollectionViewFlowLayout.
Here is my UICollectionViewFlowLayout. Any ideas what to do?
class MyFlowLayout: UICollectionViewFlowLayout {
var numberOfRows = 1
var cellPadding: CGFloat = 15.0
var availableSize = CGSize.zero
fileprivate var cache = [UICollectionViewLayoutAttributes]()
fileprivate var contentWidth: CGFloat = 0.0
fileprivate var contentHeight: CGFloat {
var collectionViewHeight = collectionView!.bounds.height
if availableSize.height > 0{
collectionViewHeight = availableSize.height
}
let insets = collectionView!.contentInset
return collectionViewHeight - (insets.top + insets.bottom)
}
func reInit(_ newSize: CGSize){
availableSize = newSize
cache.removeAll()
}
override func prepare() {
if cache.isEmpty {
let rowHeight = contentHeight / CGFloat(numberOfRows)
var yOffset = [CGFloat]()
for row in 0 ..< numberOfRows {
yOffset.append(CGFloat(row) * rowHeight )
}
var row = 0
var xOffset = [CGFloat](repeating: 0, count: numberOfRows)
for item in 0 ..< collectionView!.numberOfItems(inSection: 0) {
let indexPath = IndexPath(item: item, section: 0)
let height = rowHeight
let width = CGFloat(height / 1.27)
let frame = CGRect(x: xOffset[row], y: yOffset[row], width: width, height: height)
let insetFrame = frame.insetBy(dx: cellPadding * 2, dy: cellPadding)
let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = insetFrame
cache.append(attributes)
contentWidth = max(contentWidth, frame.maxX)
xOffset[row] = xOffset[row] + width
row = row >= (numberOfRows - 1) ? 0 : (row + 1)
}
}
}
override var collectionViewContentSize : CGSize {
return CGSize(width: contentWidth, height: contentHeight)
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
var layoutAttributes = [UICollectionViewLayoutAttributes]()
for attributes in cache {
if attributes.frame.intersects(rect) {
layoutAttributes.append(attributes)
}
}
return layoutAttributes
}
}
The layout is connected this way:
collectionView.collectionViewLayout = MyFlowLayout()
collectionView.register(MyCell.self, forCellWithReuseIdentifier: MyCell.identifier)
collectionView.dataSource = self
Prepare in MyFlowLayout is called.