1、ClassFlowLayout:

让CollectionView内容左对齐，使用固定item间距，不会因为内容充满不了一行而自动调整item间距

2、WaterfallLayout：

UICollectionView流水布局，通过cell高度排版，适配多个section的展示

使用纯Swift实现，可以直接下载并拖入项目中使用

不用实现UICollectionViewFlowLayoutDelegate，直接实现WaterfallLayoutDelegate

以下是简单的实现：

private lazy var flowLayout: WaterfallLayout = {
    let flowLayout = WaterfallLayout()
    flowLayout.scrollDirection = .vertical
    flowLayout.delegate = self
    return flowLayout
}()

extension UIViewController: WaterfallLayoutDelegate {
/// 获取流水布局item尺寸
func waterFlowLayout(_ layout: UICollectionViewFlowLayout, itemSize indexPath: IndexPath) -> CGSize {
    switch indexPath.section {
    case 0: return CGSize(width: kScreenWidth, height: 120)
    case 1: return CGSize(width: kScreenWidth, height: 90)
    case 2:return CGSize(width: kScreenWidth - 12 * 2, height: 你的流水布局cell的动态高度)
    default: return .zero
    }
}

/// 获取流水布局每个section一行几个
func waterFlowLayout(_ layout: UICollectionViewFlowLayout, numberOfColumns section: Int) -> Int {
    switch section {
    case 0: return 1
    case 1: return 1
    case 2: return 2
    default: return 0
    }
}

/// 获取流水布局每个section的边距UIEdgeInsets
func waterFlowLayout(_ layout: UICollectionViewFlowLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
    switch section {
    case 0: return UIEdgeInsets(top: 12, left: 0, bottom: 0, right: 0)
    case 1: return UIEdgeInsets(top: 12, left: 0, bottom: 0, right: 0)
    case 2: return UIEdgeInsets(top: 12, left: 12, bottom: 12, right: 12)
    default: return .zero
    }
}

/// 获取行间距
func waterFlowLayout(_ layout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
    return 12
}

/// 获取item间距
func waterFlowLayout(_ layout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
    return 12
}

}