IOS中封装自定义布局的步骤

//声明LYPWaterFlowLayout为一个类@class LYPWaterFlowLayout;@protocol LYPWaterFlowLayoutDelegate //必须实现的方法@required/**获取瀑布流每个元素的高度*/- (CGFloat)waterFlowLayout:(LYPWaterFlowLayout *)waterFlowLayout heightForItemAtIndex:(NSInteger)index itemWith:(CGFloat)itemWith;//可选实现的方法@optional/**获取瀑布流的列数*/- (NSInteger)columnCountInWaterFlowLayout:(LYPWaterFlowLayout *)waterFlowLayout;/**获取瀑布流列间距*/- (CGFloat)columnMarginInWaterFlowLayout:(LYPWaterFlowLayout *)waterFlowLayout;/**获取瀑布流的行间距*/- (CGFloat)rowMarginInWaterFlowLayout:(LYPWaterFlowLayout *)waterFlowLayout;/**获取瀑布流的内边距*/- (UIEdgeInsets)edgeInsetsInWaterFlowLayout:(LYPWaterFlowLayout *)waterFlowLayout;@end

@interface LYPWaterFlowLayout : UICollectionViewLayout/**代理*/@property (nonatomic, weak) id delegate;@end

/**默认的列数*/static const NSInteger LYPDefaultColumnCount = 3;/**默认每一列之间的间距*/static const CGFloat LYPDefaultColumMargin = 10;/**默认每一行之间的间距*/static const CGFloat LYPDefaultRowMargin = 10;/**默认边缘间距*/static const UIEdgeInsets LYPDefaultEdgeInsets = {10, 10, 10, 10};

- (NSInteger)columnCount{  //判断代理是否实现了获取列数的可选方法  if ([self.delegate respondsToSelector:@selector(columnCountInWaterFlowLayout:)])  {    //实现，返回通过代理设置的列数    return [self.delegate columnCountInWaterFlowLayout:self];  }  else  {    //为实现，返回默认的列数    return LYPDefaultColumnCount;  }}

/**所有cell的布局属性*/@property (nonatomic, strong) NSMutableArray *attrsArray;/**所有列的当前高度*/@property (nonatomic, strong) NSMutableArray *columnHeights;

/**--attrsArray--懒加载*/- (NSMutableArray *)attrsArray{  if (_attrsArray == nil)  {    _attrsArray = [NSMutableArray array];  }  return _attrsArray;}/**--columnHeights--懒加载*/- (NSMutableArray *)columnHeights{  if (_columnHeights == nil)  {    _columnHeights = [NSMutableArray array];  }  return _columnHeights;}

- (void)prepareLayout{  [super prepareLayout];  /**清除之前跟布局相关的所有属性，重新设置新的布局*/  //清除之前计算的所有列的高度  [self.columnHeights removeAllObjects];  //设置所有列的初始高度  for (NSInteger i = 0; i

- (nullable NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{  return self.attrsArray;}设置每一个cell的布局属性- (nullable UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(nonnull NSIndexPath *)indexPath{  //获取indexPath位置的布局属性  UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];  /**设置cell布局属性的frame*/  /***确定cell的尺寸***/  //获取collectionView的宽度  CGFloat collectionViewWidth = self.collectionView.frame.size.width;  //cell宽度  CGFloat width = ((collectionViewWidth - self.edgeInsets.left - self.edgeInsets.right - (self.columnCount - 1) * self.columMargin)) / self.columnCount;  //cell高度  CGFloat height = [self.delegate waterFlowLayout:self heightForItemAtIndex:indexPath.item itemWith:width];  /***设置cell的位置***/  NSInteger destColumn = 0;  CGFloat minColumnHeight = [self.columnHeights[0] doubleValue];  for (NSInteger i = 1; i columnHeight)    {      minColumnHeight = columnHeight;      destColumn = i;    }  }  //计算cell的位置  CGFloat x = self.edgeInsets.left + destColumn * (width + self.columMargin);  CGFloat y = minColumnHeight;  //判断是不是第一行  if (y != self.edgeInsets.top)  {    //若不是第一行，需要加上行间距    y += self.rowMargin;  }  /**给cell的布局属性的frame赋值*/  attrs.frame = CGRectMake(x, y, width, height);  //更新最短那列的高度  self.columnHeights[destColumn] = @(CGRectGetMaxY(attrs.frame));  /**返回indexPath位置的cell的布局属性*/  return attrs;}

- (CGSize)collectionViewContentSize{  //获取最高的那一列的高度  CGFloat maxColumnHeight = [self.columnHeights[0] doubleValue];  for (NSInteger i = 1; i