为什么我的自定义 UICollectionViewLayout 在单元格之间添加空格时会抛出错误? [英] Why does my custom UICollectionViewLayout throw an error when adding space between cells?

问题描述

我正在制作一个用于练习的自定义 UICollectionViewLayout 类，主要是试图重现单元格无限水平布置的水平流布局.

I'm making a custom UICollectionViewLayout class for practice, essentially trying to reproduce the horizontal flow layout where cells are laid out horizontally infinitely.

一切都与我的 prepare() 和 layoutAttributesForElements() 函数完美配合，如下所示:

Everything was working perfectly with my prepare() and layoutAttributesForElements() functions looking like this:

override func prepare() {
    cache.removeAll(keepingCapacity: false)

    var frame = CGRect.zero

    for item in 0..<numberOfItems {
        let indexPath = IndexPath(item: item, section: 0)
        let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        frame = CGRect(x: CGFloat(item) * width + CGFloat(item) * spacing, y: 0, width: width, height: height)
        attributes.frame = frame
        cache.append(attributes)
    }
}

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    var layoutAttributes = [UICollectionViewLayoutAttributes]()
    for attributes in cache {
        if attributes.frame.intersects(rect) {
            layoutAttributes.append(attributes)
        }
    }
    return layoutAttributes
}

当我尝试在 prepare() 中的下一行的 x 坐标中添加一组值 spacing 时出现问题，以便集合视图中的第一个单元格有一个向左的插图:

The problem arises when I try to add an inset of value spacing to the x coordinate in following line in prepare() so that the first cell in the collection view has a leftwards inset:

frame = CGRect(x: CGFloat(item) * width + CGFloat(item) * spacing, y: 0, width: width, height: height)

一旦我这样做，一切看起来都很好，直到我尝试在集合视图中滑动.抛出以下异常:

As soon as I do, everything looks well and good until I try swiping through the collection view. The following exception is thrown:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'no UICollectionViewLayoutAttributes instance for -layoutAttributesForItemAtIndexPath: <NSIndexPath: 0x618000036060> {length = 2, path = 0 - 3}'

有人能解释一下为什么会这样吗?有没有其他方法可以实现布局?

Would someone please explain why this is happening? Is there an alternative way of achieving the layout?

推荐答案

找到解决方案！显然覆盖 layoutAttributesForItem(at indexPath: IndexPath) ->UICollectionViewLayoutAttributes? 解决了这个问题！但我不知道为什么.

Found the solution! Apparently overriding layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? fixes the issue! But I have no idea why.

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