a sample for using UICollectionViewFlowLayout

gistfile1.swift

class AlignTopCollectionViewFlowLayout: UICollectionViewFlowLayout {
    
    var sectionLayout: HomeSectionLayout?
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        let attrs = super.layoutAttributesForElements(in: rect)
        var attrsCopy = [UICollectionViewLayoutAttributes]()
        let layout = sectionLayout ?? .PERSONAL
        
        for  element in attrs! {
            let elementCopy = element.copy() as! UICollectionViewLayoutAttributes

            if (elementCopy.representedElementCategory == .cell) {
                
                if layout == .EDITOR {//2 items for line
                    var offset = elementCopy.frame.origin.y

                    let yyy = (elementCopy.frame.origin.y - elementCopy.frame.size.height)
                    let divide = yyy / self.minimumLineSpacing
                    let adjust = (self.minimumLineSpacing * divide)
                    Log.d("layout == .EDITOR || layout == .SHORTCUT >> \(offset) >> \(yyy) >> \(self.minimumLineSpacing) >> divide >> \(divide) >> \(adjust)")
                    offset = offset - (self.minimumLineSpacing * divide)
                    elementCopy.frame.origin.y = offset
                }

                if layout == .EDITOR || layout == .SHORTCUT {//
                    
                    var count = collectionView?.numberOfItems(inSection: 0) ?? 0
                    count = (count / 2 + count % 2) - 1 // subtract 1 line = 3 ==> 2
                    let bottomMarginOfCollectionView = HomeSectionTableViewCell.margin / count.c //uicollectionview의 UICollectionViewFlowLayoutBreakForInvalidSizes 회피
                    
                    let divide = elementCopy.frame.origin.y / (elementCopy.frame.size.height + self.minimumLineSpacing) //calculate about line index
                    let adjustOffset = (bottomMarginOfCollectionView + self.minimumLineSpacing) * divide
                    let offset = (elementCopy.frame.origin.y - adjustOffset)
                    
                    let adjust = (self.minimumLineSpacing * divide)
                    Log.d("layout == .EDITOR || layout == .SHORTCUT >> \(offset) >> \(yyy) >> \(self.minimumLineSpacing) >> divide >> \(divide) >> \(adjust)")
                    elementCopy.frame.origin.y = offset
                } else {
                    elementCopy.frame.origin.y = 0
                }
            }
            
            attrsCopy.append(elementCopy)
        }
        
        return attrsCopy
    }
}