扩展UICollectionViewFlowLayout以提供特定部分的自定义垂直间距

Question

我正在尝试通过子类化UICollectionViewFlowLayout为页脚中的特定部分提供一些垂直间距。

-----------------------
      Footer 0
-----------------------

   vertical space from the footer = 40 ( only for the section 1)

-----------------------
      Section 1
-----------------------

我正在获取间距，但是我有一个粘性页脚，该页脚未按预期显示（此偏移也会影响页脚），并且不粘到底。

class OffsetFlowLayout: UICollectionViewFlowLayout {
    var verticalOffset: CGFloat = 0

    override func prepare() {
        super.prepare()
        verticalOffset = 40 // vertical spacing
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        guard let attributes = super.layoutAttributesForItem(at: indexPath) else { return nil }
         attributes.frame.origin.y += verticalOffset
        return attributes
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        guard let attributes = super.layoutAttributesForElements(in: rect) else {
            return nil
        }
        guard let visibleLayoutAttributes =  attributes.map( { $0.copy() }) as? [UICollectionViewLayoutAttributes] else {
            return nil
        }

        // Loop through the cache and look for items in the rect
        for attributes in visibleLayoutAttributes {
            if attributes.indexPath.section == 1 {
               attributes.frame.origin.y += verticalOffset
            }

        }

        return visibleLayoutAttributes
    }

    override func layoutAttributesForSupplementaryView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        guard let layoutAttributes = super.layoutAttributesForSupplementaryView(ofKind: elementKind, at: indexPath) else {return nil}
        if layoutAttributes.representedElementKind == UICollectionElementKindSectionHeader {
            layoutAttributes.frame.origin.y += verticalOffset
        }

        return layoutAttributes
    }

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

}

在VC中

if let layout = collectionView.collectionViewLayout as? OffsetFlowLayout {
           layout.sectionFootersPinToVisibleBounds = true
        }