Notes

import UIKit
class TwoColumnLayout: UICollectionViewFlowLayout {

// here you can define the height of each cell
let itemHeight: CGFloat = 120
let screenSize = UIScreen.main.bounds

override init() {
super.init()
setupLayout()
}

required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
setupLayout()
}

/**
Sets up the layout for the collectionView. 1pt distance between each cell and 1pt distance between each row plus use a vertical layout
*/
func setupLayout() {
minimumInteritemSpacing = 1
minimumLineSpacing = 1
scrollDirection = .vertical

//self.headerReferenceSize = CGSize(width: screenSize.width, height: 230)

}

/// here we define the width of each cell, creating a 2 column layout. In case you would create 3 columns, change the number 2 to 3
func itemWidth() -> CGFloat {
return (collectionView!.frame.width/2)-1
}

override var itemSize: CGSize {
set {
self.itemSize = CGSize(width: itemWidth(), height: itemWidth())
}
get {
return CGSize(width: itemWidth(), height: itemWidth())
}
}

override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint) -> CGPoint {
return collectionView!.contentOffset
}
}