Vertical Column Based Flow Layout

Vertical Column Based Flow Layout

class SomeUIViewControllerExample: UIViewController {
   
     override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        view.addSubview(collectionView)
        collectionView.frame = view.bounds
    }

    lazy var collectionView : UICollectionView = {
        [unowned self] in
        
        let flowLayout = ColumnBasedVerticalLayout()
        flowLayout.delegate = self
        
        var collectionView : UICollectionView = UICollectionView(frame: CGRect.zero, collectionViewLayout : ColumnBasedVerticalLayout())
        collectionView.clipsToBounds = true
        collectionView.showsVerticalScrollIndicator = false
        collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "CollectionViewCell")
        
        collectionView.delegate = self
        collectionView.dataSource = self
        collectionView.alwaysBounceVertical = true
        return collectionView
        }()
}

extension SomeUIViewControllerExample : UICollectionViewDelegate, UICollectionViewDataSource, ColumnBasedVerticalLayoutDelegate {
    
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 10
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CollectionViewCell", for: indexPath)
    
        if indexPath.row == 0 {
            cell.backgroundColor = UIColor.blue
        } else if indexPath.row == 1 {
            cell.backgroundColor = UIColor.red
        } else if indexPath.row == 2 {
            cell.backgroundColor = UIColor.orange
        } else if indexPath.row == 3 {
            cell.backgroundColor = UIColor.purple
        }else if indexPath.row == 4 {
            cell.backgroundColor = UIColor.blue
        }else if indexPath.row == 5 {
            cell.backgroundColor = UIColor.red
        }else if indexPath.row == 6 {
            cell.backgroundColor = UIColor.orange
        }else if indexPath.row == 7 {
            cell.backgroundColor = UIColor.blue
        }else if indexPath.row == 8 {
            cell.backgroundColor = UIColor.green
        }else if indexPath.row == 9 {
            cell.backgroundColor = UIColor.brown
        }else {
            cell.backgroundColor = UIColor.purple
        }
        
        return cell
    }
    
    func numberOfcolumns(in flowLayout : ColumnBasedVerticalLayout) -> Int {
        return 2
    }
    
    func flowLayout(_ flowLayout : ColumnBasedVerticalLayout, sizeForItemAtIndexPath indexPath:NSIndexPath) -> CGSize {
        
        var height = 200.0
        let width = (collectionView.bounds.width / 2.0)
        
        if indexPath.row == 0 {
            height =  380.0
        } else if indexPath.row == 1 {
            height =  300.0
        } else if indexPath.row == 2 {
            height =  300.0
        } else if indexPath.row == 3 {
            height =  300.0
        } else if indexPath.row == 4 {
            height =  380.0
        } else if indexPath.row == 5 {
            height =  300.0
        } else if indexPath.row == 6 {
            height =  300.0
        } else if indexPath.row == 7 {
            height =  300.0
        } else if indexPath.row == 8 {
            height =  300.0
        } else if indexPath.row == 9 {
            height =  300.0
        }
        
        return CGSize(width: width, height: CGFloat(height))
    }
}

protocol ColumnBasedVerticalLayoutDelegate : class {
    func flowLayout(_ flowLayout : ColumnBasedVerticalLayout, sizeForItemAtIndexPath indexPath:NSIndexPath) -> CGSize
    func numberOfcolumns(in flowLayout : ColumnBasedVerticalLayout) -> Int
}

class ColumnBasedVerticalLayout: UICollectionViewFlowLayout {
    
    weak var delegate : ColumnBasedVerticalLayoutDelegate?
    
    fileprivate var attributeCache = [UICollectionViewLayoutAttributes]()
    fileprivate var contentHeight:CGFloat  = 0.0

    override init() {
        super.init()
        minimumInteritemSpacing = 0.0
        minimumLineSpacing = 0.0
        sectionInset = UIEdgeInsets.zero
        scrollDirection = .vertical
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func prepare() {
        
        guard let delegate = delegate else {
            return
        }
    
        let numberOfColumns = delegate.numberOfcolumns(in: self)
        let columnWidth = collectionView!.bounds.width / CGFloat(numberOfColumns)
        
        var xOffset = [CGFloat]()
        
        for column in 0 ..< numberOfColumns {
            xOffset.append(CGFloat(column) * columnWidth)
        }
        
        var column = 0
        var yOffset = [CGFloat](repeating: 0, count: numberOfColumns)
        
        for item in 0 ..< collectionView!.numberOfItems(inSection: 0) {
            
            let indexPath = IndexPath(item: item, section: 0)
            
            let size = delegate.flowLayout(self, sizeForItemAtIndexPath: indexPath as NSIndexPath)
            
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = CGRect(x: xOffset[column], y: yOffset[column], width: size.width, height: size.height)
            attributeCache.append(attributes)
            
            contentHeight = max(contentHeight, attributes.frame.maxY)
            yOffset[column] = yOffset[column] + CGFloat(size.height)
            
            if column >= (numberOfColumns - 1) {
                column = 0
            } else {
                column = column + 1
            }
        }
    }
    
    override var collectionViewContentSize : CGSize {
        return CGSize(width: collectionView!.bounds.width, height: contentHeight)
    }
    
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var layoutAttributes = [UICollectionViewLayoutAttributes]()
        
        for attributes  in attributeCache {
            if attributes.frame.intersects(rect ) {
                layoutAttributes.append(attributes)
            }
        }
        return layoutAttributes
    }
}