UICollectionView autosize and dynamic number of rows

Question

I am trying to do something like this:

Basically, I am using a UICollectionView and the cells (3 diferent .xib).

So far, it works.

The thing I want to do is:

1. Set a autoheight
2. If rotate, add 1 row to the UIColectionView 2.1 If tablet, on portrait will have 2 rows and landscape 3 rows. (which basically is the same of point 2, only adding 1 row.

I have something like this:

extension ViewController {
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator){
    setSizeSize()
}

func setSizeSize(){
    if(DeviceType.IS_IPAD || UIDevice.current.orientation == .landscapeLeft || UIDevice.current.orientation == .landscapeRight){
        if let layout = myCollectionView.collectionViewLayout as? UICollectionViewFlowLayout {
            layout.estimatedItemSize = CGSize(width: 1, height: 1)
            layout.invalidateLayout()
        }
    }else{
        if let layout = myCollectionView.collectionViewLayout as? UICollectionViewFlowLayout {
            layout.estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize
            layout.invalidateLayout()
        }
    }
    myCollectionView.collectionViewLayout.invalidateLayout()
}
}

Does not work. Also, it freezes device. On simulator works parcially. (I'm trusting more device)

I also tried this, but it works sometimes...

Please, let me know if you need more info.

Thank you all in advance for the help.

Answer 1

I can suggest you to create your own UICollectionViewFlowLayout subclass which would generate needed layout. Here is a simple flow layout that you can use. You can adjust it to your needs, if I missed something.

public protocol CollectionViewFlowLayoutDelegate: class {
    func numberOfColumns() -> Int
    func height(at indexPath: IndexPath) -> CGFloat
}

public class CollectionViewFlowLayout: UICollectionViewFlowLayout {
    private var cache: [IndexPath : UICollectionViewLayoutAttributes] = [:]
    private var contentHeight: CGFloat = 0
    private var contentWidth: CGFloat {
        guard let collectionView = collectionView else {
            return 0
        }
        let insets = collectionView.contentInset
        return collectionView.bounds.width - (insets.left + insets.right)
    }

    public weak var flowDelegate: CollectionViewFlowLayoutDelegate?

    public override var collectionViewContentSize: CGSize {
        return CGSize(width: self.contentWidth, height: self.contentHeight)
    }

    public override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var layoutAttributesArray = [UICollectionViewLayoutAttributes]()
        if cache.isEmpty {
            self.prepare()
        }
        for (_, layoutAttributes) in self.cache {
            if rect.intersects(layoutAttributes.frame) {
                layoutAttributesArray.append(layoutAttributes)
            }
        }
        return layoutAttributesArray
    }

    public override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return self.cache[indexPath]
    }

    public override func prepare() {
        guard let collectionView = self.collectionView else {
            return
        }
        let numberOfColumns = self.flowDelegate?.numberOfColumns() ?? 1
        let cellPadding: CGFloat = 8
        self.contentHeight = 0
        let columnWidth = UIScreen.main.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 photoHeight = self.flowDelegate?.height(at: indexPath) ?? 1
            let height = cellPadding * 2 + photoHeight
            let frame = CGRect(x: xOffset[column], y: yOffset[column], width: columnWidth, height: height)
            let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)
            let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
            attributes.frame = insetFrame
            self.cache[indexPath] = attributes
            self.contentHeight = max(self.contentHeight, frame.maxY)
            yOffset[column] = yOffset[column] + height
            column = column < (numberOfColumns - 1) ? (column + 1) : 0
        }
    }
}

Now in your UIViewController you can use it like this:

override func viewDidLoad() {
    super.viewDidLoad()
    let flowLayout = CollectionViewFlowLayout()
    flowLayout.flowDelegate = self
    self.collectionView.collectionViewLayout = flowLayout
}

invalidate collectionView layout after orientation would be changed

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    guard let flowLayout = self.collectionView.collectionViewLayout as? CollectionViewFlowLayout else {
        return
    }
    flowLayout.invalidateLayout()
}

and now make your ViewController conform to CollectionViewFlowLayoutDelegate

extension ViewController: CollectionViewFlowLayoutDelegate {
    func height(at indexPath: IndexPath) -> CGFloat {
        guard let cell = self.collectionView.cellForItem(at: indexPath) else {
            return 1
        }
        cell.layoutIfNeeded()
        //get calculated cell height
        return cell.systemLayoutSizeFitting(UILayoutFittingCompressedSize).height
    }

    func numberOfColumns() -> Int {
        //how much columns would be shown, depends on orientation
        return UIDevice.current.orientation == .portrait ? 2 : 3
    }
}