UICollectionViewLayout‘冻结’

Question

我是一个快速/iOS noobie，我开始认为我已经把珠穆朗玛峰作为我的第一个任务。无论如何，我的应用程序有一个基于周滚动的日历视图。我正在使用自定义的UICollectionViewLayout。当应用程序启动时，一切看起来都很好，我可以在24小时内向下滚动，直到白天(见第一张图片)。

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当用户到达预定义的单元格数(天数)结束时，会向数据源添加更多的单元格。我可以愉快地继续滚动，代码可以根据需要添加更多的单元格。

问题是：

当我停止滚动在任何额外的数据(天)被添加到数据源后的日子，然后重新开始滚动布局冻结在一个单一的块，只是浮动(见第二个图像)。

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正确的单元格放置(钉扎)到视图顶部不再工作(因为它只是上述冻结的单元格块)，并且不显示新的单元格。

奇怪的是，在布局冻结之后，终端继续从UICollectionViewLayout注销调试，将单元格放置在正确的位置，尽管UICollectionViewController似乎已经停止监听了吗？

打印在“日期”单元格的终端中：Cell attributes: <UICollectionViewLayoutAttributes: 0x6080003edf00> index path: (<NSIndexPath: 0x60800003a760> {length = 2, path = 2 - 0}); frame = (1033 235; 47 50); zIndex = 1024;

从视图层次结构调试：(UICollectionView): <UICollectionView: 0x7feb7302d000; frame = (0 0; 667 375); clipsToBounds = YES; autoresize = RM+BM; gestureRecognizers = <NSArray: 0x600000051490>; layer = <CALayer: 0x6000000329a0>; contentOffset: {1033, 235}; contentSize: {2651, 910}> collection view layout: <V3.CDCLayout: 0x7feb7140f1a0>

从“日期”单元格的视图层次结构调试：<V3.CDCMonthCell: 0x7feb7410a690; baseClass = UICollectionViewCell; frame = (1201.5 361; 47 50); clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x608000035180>>

更新

嗨，罗伯-我试着把我的代码拿回来，然后又跟着几个教程，当我添加我的数据源(单例)时，这些教程都以相同的问题结束--所以有一个热门的嫌疑人(！)但我就是搞不懂。下面的代码基于一个教程示例，但显示了相同的问题。

CollectionViewController：

private let reuseIdentifier = "cCell"

class CustomCollectionViewController: UICollectionViewController {

    let localItems = Items.items.getItems()


    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 6  }


    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return Items.items.getItemCount()
    }

    override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {

        if (Items.items.getItemCount() - indexPath.row ) == 2 {
            Items.items.addItems()
            collectionView.reloadData()
            collectionView.collectionViewLayout.invalidateLayout()
        }
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> CustomCollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! CustomCollectionViewCell

        cell.textLabel.text = "SEC=\(indexPath.section),IXDI=\(indexPath.item)"

        return cell
    }
}

布局：

class CustomCollectionViewLayout: UICollectionViewLayout {

    let CELL_HEIGHT = 145.0
    let CELL_WIDTH = 145.0
    let STATUS_BAR = UIApplication.shared.statusBarFrame.height
    var cellAttrsDictionary = Dictionary<IndexPath, UICollectionViewLayoutAttributes>()
    var contentSize = CGSize.zero

    override var collectionViewContentSize : CGSize {
        return contentSize
    }

    override func invalidateLayout() {
        super.invalidateLayout()
        cellAttrsDictionary.removeAll()
    }

    override func prepare() {

        if (collectionView?.numberOfSections)! > 0 {
            for section in 0...collectionView!.numberOfSections-1 {

               if (collectionView?.numberOfItems(inSection: section))! > 0 {
                    for item in 0...collectionView!.numberOfItems(inSection: section)-1 {

                        let cellIndex = IndexPath(item: item, section: section)
                        let xPos = Double(item) * CELL_WIDTH
                        let yPos = Double(section) * CELL_HEIGHT

                        let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndex)
                        cellAttributes.frame = CGRect(x: xPos, y: yPos, width: CELL_WIDTH, height: CELL_HEIGHT)

                        if section == 0 && item == 0 {
                            cellAttributes.zIndex = 4
                        } else if section == 0 {
                            cellAttributes.zIndex = 3
                        } else if item == 0 {
                            cellAttributes.zIndex = 2
                        } else {
                            cellAttributes.zIndex = 1
                        }

                        cellAttrsDictionary[cellIndex] = cellAttributes
                    }
                }
            }
        }

        let contentWidth = Double(collectionView!.numberOfItems(inSection: 0)) * CELL_WIDTH
        let contentHeight = Double(collectionView!.numberOfSections) * CELL_HEIGHT
        self.contentSize = CGSize(width: contentWidth, height: contentHeight)
    }

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

        for cellAttributes in cellAttrsDictionary.values {
            if rect.intersects(cellAttributes.frame) {
                attributesInRect.append(cellAttributes)
            }
        }
        return attributesInRect
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return cellAttrsDictionary[indexPath]!
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        return true
    }
}

项目/数据-源/单例：

class Items {

    static var items = Items() // Singleton

    var classItems = [Int]()

    init() {
        addItems()
    }

    func getItemCount() -> Int {
        return classItems.count
    }

    func getItems() -> [Int] {
        return classItems
    }

    func addItems() {
        for i in 1 ... 7 {
            classItems.append(i)
        }
    }

}

Answer 1

在我的测试中，重新加载willDisplay中的数据源似乎是问题的根源。通过DispatchQueue.main.async { ... }，问题似乎消失了。

private var lastReloadedRow = 0

override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    if (Items.items.getItemCount() - indexPath.row) == 2 && lastReloadedRow < indexPath.row {
        lastReloadedRow = indexPath.row
        DispatchQueue.main.async {
            Items.items.addItems()
            collectionView.reloadData()
        }
    }
}

注意，我添加了一个state属性来跟踪我们是否已经加载了，因为按照它的方式，它是多次不必要地重新加载的。

为了完整起见，这里是我对您的自定义布局的完整实现。我做了几件无关的事：

• 简化的layoutAttributesForElements(in:)；以及
• 关闭shouldInvalidateLayout(forBoundsChange:)，因为您需要重新构建字典。

因此：

class CustomCollectionViewLayout: UICollectionViewLayout {

    let CELL_HEIGHT = 145.0
    let CELL_WIDTH = 145.0
    let STATUS_BAR = UIApplication.shared.statusBarFrame.height
    var cellAttrsDictionary = Dictionary<IndexPath, UICollectionViewLayoutAttributes>()
    var contentSize = CGSize.zero

    override var collectionViewContentSize : CGSize {
        return contentSize
    }

    override func invalidateLayout() {
        super.invalidateLayout()
        cellAttrsDictionary.removeAll()
    }

    override func prepare() {
        if collectionView!.numberOfSections > 0 {
            for section in 0 ..< collectionView!.numberOfSections {
                if collectionView!.numberOfItems(inSection: section) > 0 {
                    for item in 0 ..< collectionView!.numberOfItems(inSection: section) {
                        let cellIndex = IndexPath(item: item, section: section)
                        let xPos = Double(item) * CELL_WIDTH
                        let yPos = Double(section) * CELL_HEIGHT

                        let cellAttributes = UICollectionViewLayoutAttributes(forCellWith: cellIndex)
                        cellAttributes.frame = CGRect(x: xPos, y: yPos, width: CELL_WIDTH, height: CELL_HEIGHT)

                        cellAttrsDictionary[cellIndex] = cellAttributes
                    }
                }
            }
        }

        let contentWidth = Double(collectionView!.numberOfItems(inSection: 0)) * CELL_WIDTH
        let contentHeight = Double(collectionView!.numberOfSections) * CELL_HEIGHT
        contentSize = CGSize(width: contentWidth, height: contentHeight)
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return cellAttrsDictionary.values.filter { $0.frame.intersects(rect) }
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        return cellAttrsDictionary[indexPath]!
    }

    // override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
    //     return true
    // }
}