如何确定自定义 UICollectionViewCell 何时在屏幕上显示为 100%

Question

从上图中我有 UICollectionView 和 4 个自定义单元格。屏幕上可以随时显示 2 或 3 个单元格。我如何判断 "cell 1" 或 "cell 2" 何时在屏幕上显示为 100%？

两者都

collectionView.visibleCells
collectionView.indexPathsForVisibleItems

return 数组，但不会告诉您哪个单元格 100% 显示在屏幕上。

在图片的情况下，以下将显示在didSelectItemAt

collectionView.visibleCells

[<Shot_On_Goal.MainCollectionViewCell: 0x101f525c0; baseClass = UICollectionViewCell; frame = (190 7.66667; 454 350); clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x1c0237300>>, <Shot_On_Goal.HeaderCollectionViewCell: 0x101f4d580; baseClass = UICollectionViewCell; frame = (10 0; 170 365); clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x1c0236800>>, <Shot_On_Goal.TheirHockeyNetCollectionViewCell: 0x101f55520; baseClass = UICollectionViewCell; frame = (654 7.66667; 454 350); clipsToBounds = YES; opaque = NO; layer = <CALayer: 0x1c0238fe0>>]

collectionView.indexPathsForVisibleItems

[[0, 1], [0, 0], [0, 2]]

Answer 1

您可以过滤 visibleCells 数组以检查单元格的框架是否包含在 collectionView 的框架中：

    var visibleCells = self.collectionView?.visibleCells
    visibleCells = visibleCells?.filter({ cell -> Bool in
        return self.collectionView?.frame.contains(cell.frame) ?? false
    })
    print (visibleCells)

Answer 2

这将为完全可见的单元格 return 一个索引路径数组：

func fullyVisibleCells(_ inCollectionView: UICollectionView) -> [IndexPath] {

    var returnCells = [IndexPath]()

    var vCells = inCollectionView.visibleCells
    vCells = vCells.filter({ cell -> Bool in
        let cellRect = inCollectionView.convert(cell.frame, to: inCollectionView.superview)
        return inCollectionView.frame.contains(cellRect) 
    })

    vCells.forEach({
        if let pth = inCollectionView.indexPath(for: [=10=]) {
            returnCells.append(pth)
        }
    })

    return returnCells

}

@IBAction func test(_ sender: Any) {

    let visCells = fullyVisibleCells(self.collectionView)
    print(visCells)

}

Answer 3

这是它的扩展，基于 don DonMag 的回答：

extension UICollectionView {
    var fullyVisibleCells : [UICollectionViewCell] {
        return self.visibleCells.filter { cell in
            let cellRect = self.convert(cell.frame, to: self.superview)
            return self.frame.contains(cellRect) }
    }
}

如何确定自定义 UICollectionViewCell 何时在屏幕上显示为 100%

How to determine when a custom UICollectionViewCell is 100% on the screen

ios

uicollectionview

uicollectionviewcell

swift