// 每一列的間距static const CGFloat MKJDefaultColumnMargin = 10;// 每一行間距static const CGFloat MKJDefaultRowMargin = 10;// 整體的上間距，左間距，下間距，右間距static const UIEdgeInsets MKJDefaultEdgeInsets = {10,10,10,10};// 默認是多少列static const NSUInteger MKJDefaultColumnCounts = 2;@interface MKJWaterFallLayout ()@property (nonatomic,strong) NSMutableArray *attributeArr; // cell屬性的數組@property (nonatomic,strong) NSMutableArray *columnHeightArr; // 每列的高度數組@end

// 每次刷新會調用一次- (void)prepareLayout{  [super prepareLayout];  // 每次重新刷新的時候清除之前的所有高度值，默認就是UIEdg給定的top  [self.columnHeightArr removeAllObjects];  for (NSInteger i = 0; i < [self columnCount]; i++) {    [self.columnHeightArr addObject:@([self insetMargin].top)];  }  // 每次刷新把對應的att屬性清空  [self.attributeArr removeAllObjects];  // 初始化一次每個cell對應的attribute屬性  NSInteger count = [self.collectionView numberOfItemsInSection:0];  for (NSInteger i = 0; i < count; i++) {    NSIndexPath *indexpath = [NSIndexPath indexPathForItem:i inSection:0];    UICollectionViewLayoutAttributes *attribute = [self layoutAttributesForItemAtIndexPath:indexpath];    [self.attributeArr addObject:attribute];  }}

// 返回attribute屬性數組決定最后的排布- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{  return self.attributeArr;}// 返回對應的indexpath下每個cell的屬性 cell的出現會一直刷新該方法- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{  // 初始化布局屬性---> 對應的indexpath  UICollectionViewLayoutAttributes *att = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];  CGFloat collectionW = self.collectionView.frame.size.width;  // 寬度是根據列數和間距固定算出來的  CGFloat width = (collectionW - [self insetMargin].left - [self insetMargin].right - ([self columnCount] - 1) * [self columnMargin]) / [self columnCount];  // 高度是根據代理的數據源返回比例計算的  CGFloat height = [self.delegate MKJWaterFallLayout:self heightForItemAtIndexPath:indexPath] * width;  // X 和 Y值都是在找出最小column之后才能確定，核心就是根據列數，找出最小高度的那一列  // 先取出第一個默認是最小的  CGFloat minColumnHeight = [self.columnHeightArr[0] doubleValue];  // 默認最小的是第0列  NSUInteger finalCol = 0;  for (NSInteger i = 1 ; i < [self columnCount]; i++) {    CGFloat currentColHeight = [self.columnHeightArr[i] doubleValue];    if (minColumnHeight > currentColHeight) {      minColumnHeight = currentColHeight;      finalCol = i;    }  }  // x，y值是根據最小高度列算出來的  CGFloat x = [self insetMargin].left + (width + [self columnMargin]) * finalCol;  CGFloat y = minColumnHeight;  // 當你是一個行排布的時候 默認是top值，不需要加間距  NSInteger count = indexPath.item;  if ((count / ([self columnCount])) >= 1) {    y += [self rowMargin];  }  att.frame = CGRectMake(x, y, width, height);  self.columnHeightArr[finalCol] = @(CGRectGetMaxY(att.frame));  return att;}

// 計算出滾動區域的大小- (CGSize)collectionViewContentSize{  CGFloat maxColumHeight = [self.columnHeightArr[0] doubleValue];  for (NSInteger i = 1; i < [self columnCount]; i++) {    CGFloat currentColHeight = [self.columnHeightArr[i] doubleValue];    if (maxColumHeight < currentColHeight) {      maxColumHeight = currentColHeight;    }  }  return CGSizeMake(0, maxColumHeight + [self insetMargin].bottom);}

// 聲明如下- (UICollectionView *)colletionView{  if (_colletionView == nil) {    MKJWaterFallLayout *layout = [[MKJWaterFallLayout alloc] init];    layout.delegate = self;    UICollectionView *collectionV = [[UICollectionView alloc] initWithFrame:[UIScreen mainScreen].bounds collectionViewLayout:layout];    collectionV.backgroundColor = [UIColor redColor];    [collectionV registerNib:[UINib nibWithNibName:productID bundle:nil] forCellWithReuseIdentifier:productID];    collectionV.delegate = self;    collectionV.dataSource = self;    _colletionView = collectionV;  }  return _colletionView;}// 內部行數，間距的控制#pragma mark - waterfallLayoutDelegate- (CGFloat)MKJWaterFallLayout:(MKJWaterFallLayout *)layout heightForItemAtIndexPath:(NSIndexPath *)indexPath{  // 返回寬度和高度比例  MKJProductModel *product = self.dataSource[indexPath.item];  return product.h / product.w;}// 控制列間距- (CGFloat)columnMarginForWaterFallLayout:(MKJWaterFallLayout *)collectionViewLayout{  return 10;}// 控制行間距- (CGFloat)rowMarginForWaterFallLayout:(MKJWaterFallLayout *)collectionViewLayout{  return 30;}// 控制列數- (NSUInteger)columnCountForWaterFallLayout:(MKJWaterFallLayout *)collectionViewLayout{//  if (self.dataSource.count > 50) {//    return 3;//  }  return 3;}// 控制整體上左下右間距- (UIEdgeInsets)insetForWaterFallLayout:(MKJWaterFallLayout *)collectionViewLayout{  return UIEdgeInsetsMake(10, 10, 10, 10);}