ios - 使用自定义 Collection View 布局快速配置动态单元格高度

Question

我有一个自定义 Collection View 布局，它从下往上加载消息应用程序的单元格，但我在实现动态单元格高度时遇到了麻烦。我相信我连接的用于检索动态单元格高度的协议(protocol)和委托(delegate)适用于每个单元格(这是我通过打印每个 indexPath.item 的高度推断出来的)，除非在 collectionView 加载单元格高度时不是他们应该有的高度。它们都只是一个静态高度(不是 var cellHeight 预设的 80)并且只显示一行文本。

 protocol InvertedStackProtocol: class {
    func collectionView(_ collectionView: UICollectionView, heightForCellAtIndexPath indexPath: IndexPath) -> CGFloat
    }

    class InvertedStackLayout: UICollectionViewLayout, UICollectionViewDelegateFlowLayout {

    var cellHeight: CGFloat = 80

    weak var delegate: InvertedStackProtocol!

    override func prepare() {

        guard let collectionView = self.collectionView else {return}

        for item in 0 ..< collectionView.numberOfItems(inSection: 0) {
            let indexPath = IndexPath(item: item, section: 0)
            let height = delegate.collectionView(collectionView, heightForCellAtIndexPath: indexPath)
            print (height, indexPath.item)
            cellHeight = height
        }

    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var layoutAttrs = [UICollectionViewLayoutAttributes]()

        if let collectionView = self.collectionView {
            for section in 0 ..< collectionView.numberOfSections {
                if let numberOfSectionItems = numberOfItemsInSection(section) {
                    for item in 0 ..< numberOfSectionItems {
                        let indexPath = IndexPath(item: item, section: section)
                        let layoutAttr = layoutAttributesForItem(at: indexPath)

                        if let layoutAttr = layoutAttr, layoutAttr.frame.intersects(rect) {
                            layoutAttrs.append(layoutAttr)
                        }
                    }
                }
            }
        }

        return layoutAttrs
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let layoutAttr = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        let contentSize = self.collectionViewContentSize

        layoutAttr.frame = CGRect(
            x: 0, y: contentSize.height - CGFloat(indexPath.item + 1) * cellHeight,
            width: contentSize.width, height: cellHeight)

        return layoutAttr
    }

    func numberOfItemsInSection(_ section: Int) -> Int? {
        if let collectionView = self.collectionView,
            let numSectionItems = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: section)
        {
            return numSectionItems
        }

        return 0
    }

    override var collectionViewContentSize: CGSize {
        get {
            var height: CGFloat = 0.0
            var bounds = CGRect.zero

            if let collectionView = self.collectionView {
                for section in 0 ..< collectionView.numberOfSections {
                    if let numItems = numberOfItemsInSection(section) {
                        height += CGFloat(numItems) * cellHeight
                    }
                }

                bounds = collectionView.bounds
            }

            return CGSize(width: bounds.width, height: max(height, bounds.height))
            // return CGSize(width: bounds.width, height: height) do this for more exact fit of collection view
        }
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        if let oldBounds = self.collectionView?.bounds,
            oldBounds.width != newBounds.width || oldBounds.height != newBounds.height
        {
            return true
        }

        return false
    }
}

Answer 1

使用此方法可以更改 UICollectionViewCell 的高度。

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: 125.0, height: 175.0)
}