let layout = WaterfallMutiSectionFlowLayout()
layout.delegate = self
let collection = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
/// collectionItem高度
func heightForRowAtIndexPath(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, indexPath: IndexPath, itemWidth: CGFloat) -> CGFloat
/// 每个section 列数(默认2列)
@objc optional func columnNumber(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> Int
/// header高度(默认为0)
@objc optional func referenceSizeForHeader(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> CGSize
/// footer高度(默认为0)
@objc optional func referenceSizeForFooter(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> CGSize
/// 每个section 边距(默认为0)
@objc optional func insetForSection(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> UIEdgeInsets
/// 每个section item上下间距(默认为0)
@objc optional func lineSpacing(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> CGFloat
/// 每个section item左右间距(默认为0)
@objc optional func interitemSpacing(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> CGFloat
/// section头部header与上个section尾部footer间距(默认为0)
@objc optional func spacingWithLastSection(collectionView collection: UICollectionView, layout: WaterfallMutiSectionFlowLayout, section: Int) -> CGFloat