Swift UICollectionView横向分页滚动，cell左右排版

废话不多说，直接上代码

自定义一个SYitemViewLayout，继承UICollectionViewFlowLayout

mport UIKit

//根据需求设置列跟行
let kEmotionCellNumberOfOneRow = 3
let kEmotionCellRow = 2

class SYitemViewLayout: UICollectionViewFlowLayout {
    
    // 保存所有item
    fileprivate var attributesArr: [UICollectionViewLayoutAttributes] = []
    
    // MARK:- 重新布局
     override func prepare() {
         super.prepare()
         
         let itemWH: CGFloat = (kScreenWitdh - 30) / CGFloat(kEmotionCellNumberOfOneRow)
         
         // 设置itemSize
         itemSize = CGSize(width: itemWH, height: itemWH - 50)
         minimumLineSpacing = 0
         minimumInteritemSpacing = 0
         scrollDirection = .horizontal
         
         // 设置collectionView属性
         collectionView?.isPagingEnabled = true
         collectionView?.showsHorizontalScrollIndicator = false
         collectionView?.showsVerticalScrollIndicator = true
//         let insertMargin = (collectionView!.bounds.height - 3 * itemWH) * 0.5
//        collectionView?.contentInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
         
         var page = 0
         let itemsCount = collectionView?.numberOfItems(inSection: 0) ?? 0
         for itemIndex in 0..<itemsCount {
             let indexPath = IndexPath(item: itemIndex, section: 0)
             let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
             
             page = itemIndex / (kEmotionCellNumberOfOneRow * kEmotionCellRow)
             // 通过一系列计算, 得到x, y值
             let x = itemSize.width * CGFloat(itemIndex % Int(kEmotionCellNumberOfOneRow)) + (CGFloat(page) * (kScreenWitdh - 30))
             let y = itemSize.height * CGFloat((itemIndex - page * kEmotionCellRow * kEmotionCellNumberOfOneRow) / kEmotionCellNumberOfOneRow)
             
             attributes.frame = CGRect(x: x, y: y, width: itemSize.width, height: itemSize.height)
             // 把每一个新的属性保存起来
             attributesArr.append(attributes)
         }
         
     }
     
     override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
         var rectAttributes: [UICollectionViewLayoutAttributes] = []
         _ = attributesArr.map({
             if rect.contains($0.frame) {
                 rectAttributes.append($0)
             }
         })
         return rectAttributes
     }
}