瀑布流的实现

/**
   *  collectionView上下左右之间的间距
   */
  @property(nonatomic,assign) UIEdgeInsets sectionInset;
  /**
   *  每一列之间的间距
   */
  @property(nonatomic,assign) CGFloat columnMargin1;
  /**
   *  每一行之间的间距
   */
  @property(nonatomic,assign) CGFloat rowMargin1;
  /**
   *  告诉外界你想显示多少列
   */
  @property(nonatomic,assign) int columnsCount;

#pragma mark - <CWWaterViewLayoutDelegate>的代理方法
-(CGFloat)waterflowLayout:(CWWaterViewLayout *)waterViewLayout heightForWidth:(CGFloat)width atIndexPath:(NSIndexPath *)indexPath
{
   ShopModel *shopmodel = self.tempArray[indexPath.item];
   /**
    *  取出来宽高
    */
  NSString *shopH = [NSString stringWithFormat:@"%@",shopmodel.H];
  NSString *shopW = [NSString stringWithFormat:@"%@",shopmodel.W];
  /**
    *  转化为float类型
    */
  CGFloat shopHValue = [shopH floatValue];
  CGFloat shopWValue = [shopW floatValue];
  /**
   *  返回比例计算的高度
   */
  return shopHValue / shopWValue * width;
}

#pragma mark5.  尺寸的计算
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
/**
 *  假设最短的那一列是第0列
 */
__block NSString *minYColun = @"0";
[self.maxYdict enumerateKeysAndObjectsUsingBlock:^(NSString *column,NSNumber *maxY, BOOL * _Nonnull stop) {
    if ([maxY floatValue] < [self.maxYdict[minYColun] floatValue] ) {
        minYColun = column;
    }
}];
/**
 *  计算宽度
 */
CGFloat width =  (self.collectionView.frame.size.width - self.sectionInset.left - self.sectionInset.right - (self.columnsCount - 1) * self.columnMargin1)/self.columnsCount;
/**
 *  高度
 */
CGFloat height = [self.delegate waterflowLayout:self heightForWidth:width atIndexPath:indexPath];
/**
 *  计算x和y
 */
CGFloat x = self.sectionInset.left + (width + self.columnMargin1) * [minYColun floatValue];
CGFloat y = [self.maxYdict[minYColun]floatValue] + self.rowMargin1;
/**
 *  更新这一列的最大Y值
 */
  self.maxYdict[minYColun] = @(y + height);
  UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
  attrs.frame = CGRectMake(x, y, width, height);
  return attrs;
}