/** 初始化 生成每个视图的布局信息*/
-(void)prepareLayout;
/** 决定一段区域所有cell和头尾视图的布局属性*/
-(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect ;
/** 返回indexPath位置cell对应的布局属性*/
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
/** 返回indexPath位置头和脚视图对应的布局属性*/
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;
//返回内容高度
-(CGSize)collectionViewContentSize;

typedef enum {
    WSLWaterFlowVerticalEqualWidth = 0, /** 竖向瀑布流 item等宽不等高 */
    WSLWaterFlowHorizontalEqualHeight = 1, /** 水平瀑布流 item等高不等宽 不支持头脚视图*/
    WSLWaterFlowVerticalEqualHeight = 2,  /** 竖向瀑布流 item等高不等宽 */
    WSLWaterFlowHorizontalGrid = 3,  /** 特为国务院客户端原创栏目滑块样式定制-水平栅格布局  仅供学习交流*/
    WSLLineWaterFlow = 4 /** 线性布局 待完成，敬请期待 */
} WSLFlowLayoutStyle; //样式

@class WSLWaterFlowLayout;

@protocol WSLWaterFlowLayoutDelegate <NSObject>

/**
 返回item的大小
 注意：根据当前的瀑布流样式需知的事项：
 当样式为WSLWaterFlowVerticalEqualWidth 传入的size.width无效 ，所以可以是任意值，因为内部会根据样式自己计算布局
 WSLWaterFlowHorizontalEqualHeight 传入的size.height无效 ，所以可以是任意值 ，因为内部会根据样式自己计算布局
 WSLWaterFlowHorizontalGrid   传入的size宽高都有效， 此时返回列数、行数的代理方法无效，
 WSLWaterFlowVerticalEqualHeight 传入的size宽高都有效， 此时返回列数、行数的代理方法无效
 */
- (CGSize)waterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;

/** 头视图Size */
-(CGSize )waterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout sizeForHeaderViewInSection:(NSInteger)section;
/** 脚视图Size */
-(CGSize )waterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout sizeForFooterViewInSection:(NSInteger)section;

@optional  //以下都有默认值
/** 列数*/
-(CGFloat)columnCountInWaterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout;
/** 行数*/
-(CGFloat)rowCountInWaterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout;

/** 列间距*/
-(CGFloat)columnMarginInWaterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout;
/** 行间距*/
-(CGFloat)rowMarginInWaterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout;
/** 边缘之间的间距*/
-(UIEdgeInsets)edgeInsetInWaterFlowLayout:(WSLWaterFlowLayout *)waterFlowLayout;

@end

@interface WSLWaterFlowLayout : UICollectionViewLayout

/** delegate*/
@property (nonatomic, weak) id<WSLWaterFlowLayoutDelegate> delegate;
/** 瀑布流样式*/
@property (nonatomic, assign) WSLFlowLayoutStyle  flowLayoutStyle;

@end

    WSLWaterFlowLayout * _flow = [[WSLWaterFlowLayout alloc] init];
    _flow.delegate = self;
    _flow.flowLayoutStyle = WSLVerticalWaterFlow;