CollectinView分组不会显示最后一个组中的所有项目

class CustomFlowLayout: UICollectionViewFlowLayout {
    override func prepare() {
        super.prepare()
        
        guard let collectionView = collectionView else {
            return
        }
        
        // 遍历所有的分组
        for section in 0..<collectionView.numberOfSections {
            let itemCount = collectionView.numberOfItems(inSection: section)
            
            // 计算每个分组的大小和位置
            var sectionFrame = CGRect.zero
            var itemAttributes: [UICollectionViewLayoutAttributes] = []
            
            for item in 0..<itemCount {
                let indexPath = IndexPath(item: item, section: section)
                let itemSize = delegate?.collectionView?(collectionView, layout: self, sizeForItemAt: indexPath) ?? self.itemSize
                
                let itemAttributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
                itemAttributes.frame = CGRect(x: xOffset, y: yOffset, width: itemSize.width, height: itemSize.height)
                
                // 更新分组的大小
                sectionFrame = sectionFrame.union(itemAttributes.frame)
                
                itemAttributes.append(itemAttributes)
            }
            
            // 调整分组的大小和间距
            sectionFrame.size.width = collectionView.bounds.width
            sectionFrame.origin.x = 0
            
            sectionFrame.origin.y = yOffset
            yOffset = sectionFrame.maxY + minimumLineSpacing
            
            // 更新布局属性
            sectionAttributes.append(itemAttributes)
        }
        
        // 更新collectionView的内容大小
        contentSize = CGSize(width: collectionView.bounds.width, height: yOffset)
    }
}