使用自定義集合視圖布局快速配置動態單元格高度

Question

我有一個自定義的集合視圖布局，該布局從下至上為消息傳遞應用程序加載了單元格，但我在實現動態單元格高度時遇到了麻煩。 我相信我掛鈎來檢索動態單元格高度的協議和委托對於每個單元格都有效（這是我從打印每個indexPath.item的高度indexPath.item ），除了在加載collectionView時，單元格的高度不是他們應該假定的高度成為。 它們都是一個靜態高度（不是var cellHeight預設的80），並且只顯示一行文本。

 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高度UICollectionViewCell。

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