UICollectionView 的布局默认是当前行内适应，如果cell的宽度超过当前的行宽度就会放到下一行，但是当前行内的多个cell会等距离分布，而不能像效果图中等间距靠left 或者right分布。

如图效果

/// 让列间距固定为minimumInteritemSpacing
class AiUgcReportFlowLayout: UICollectionViewFlowLayout {
    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        if let attris = super.layoutAttributesForElements(in: rect) {
            for (i, att) in attris.enumerated() {
                if i>0 {
                    let cur = att
                    let pre = attris[i-1]
                    // 这里 indexPath 一定要判断，坑了半天，fuck
                    if cur.indexPath == pre.indexPath {
                        let preMaxX = pre.frame.maxX
                        //根据  maximumInteritemSpacing 计算出的新的 x 位置
                        let targetX = preMaxX + self.minimumInteritemSpacing;
                        if targetX < cur.frame.maxX && (targetX+cur.frame.width) < self.collectionViewContentSize.width {
                            var curFrame = cur.frame
                            curFrame.origin.x = targetX
                            cur.frame = curFrame
                        }
                    }
                    
                }
            }
            return attris
        }
        return super.layoutAttributesForElements(in: rect)
    }
}

😀 😀 😀 😀 提供oc 版本，直接用吧骚年😀 😀 😀

- (NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray *attris = [super layoutAttributesForElementsInRect:rect];
    for (int i = 0; i< attris.count; i++) {
        if (i>0) {
            
            UICollectionViewLayoutAttributes *curAtt = attris[i];
            UICollectionViewLayoutAttributes *preAtt = attris[i-1];
            // 这里 indexPath 一定要判断，坑了半天，fuck
            if (curAtt.indexPath == preAtt.indexPath) {
                CGFloat curMaxX = curAtt.frame.origin.x+curAtt.frame.size.width;
                CGFloat preMaxX = preAtt.frame.origin.x+preAtt.frame.size.width;
                CGFloat targetX = preMaxX + self.minimumInteritemSpacing;
                if ((targetX < curMaxX) && (targetX+curAtt.frame.size.width) < self.collectionView.bounds.size.width) {
                    CGRect curFrame = curAtt.frame;
                    curFrame.origin.x = targetX;
                    curAtt.frame = curFrame;
                }
            }
        }
    }
    
    return attris;

}