how to set the spacing of a collection view swift
// Do any additional setup after loading the view, typically from a nib.
let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
layout.sectionInset = UIEdgeInsets(top: 20, left: 0, bottom: 10, right: 0)
layout.itemSize = CGSize(width: screenWidth/3, height: screenWidth/3)
layout.minimumInteritemSpacing = 0
layout.minimumLineSpacing = 0
collectionView!.collectionViewLayout = layout