swift – UICollectionView自动调整大小和动态行数

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()
}
}

我建议你创建自己的UICollectionViewFlowLayout子类,它将生成所需的布局.这是一个可以使用的简单流程布局.如果我错过了什么,你可以根据自己的需要调整它.

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
        }
    }
}

现在在你的UIViewController中你可以像这样使用它：

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

在更改方向后,使collectionView布局无效

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

现在使ViewController符合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
    }
}