具体实现如下：
LYFWaterflowLayout.h
#import <UIKit/UIKit.h>
@class LYFWaterflowLayout;
@protocol LYFWaterflowLayoutDelegate@required
/** cell高度 */
- (CGFloat)waterflowLayout:(LYFWaterflowLayout *)waterflowLayout heightForItemAtIndex:(NSUInteger)index itemWidth:(CGFloat)itemWidth;
@optional
/** 行数或列数（默认3 */
- (CGFloat)columnCountInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout;
/** 列间距 */
- (CGFloat)columnMarginInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout;
/** 行间距 */
- (CGFloat)rowMarginInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout;
/** 内边距 */
- (UIEdgeInsets)edgeInsetsInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout;
@end
@interface LYFWaterflowLayout : UICollectionViewLayout
/** 代理 */
@property (nonatomic, weak) iddelegate;
@end
LYFWaterflowLayout.m
/** 默认的列数 */
static const NSInteger LYFDefaultColumnCount = 3;
/** 每一列之间的间距 */
static const CGFloat LYFDefaultColumnMargin = 10;
/** 每一行之间的间距 */
static const CGFloat LYFDefaultRowMargin = 10;
/** 边缘间距 */
static const UIEdgeInsets LYFDefaultEdgeInsets = {10, 10, 10, 10};
@interface LYFWaterflowLayout()
/** 存放所有cell的布局属性 */
@property (nonatomic, strong) NSMutableArray *attrsArray;
/** 存放所有列的当前高度 */
@property (nonatomic, strong) NSMutableArray *columnHeights;
/** 内容的高度 */
@property (nonatomic, assign) CGFloat contentHeight;
- (CGFloat)rowMargin;
- (CGFloat)columnMargin;
- (NSInteger)columnCount;
- (UIEdgeInsets)edgeInsets;
@end
@implementation LYFWaterflowLayout
#pragma mark - 常见数据处理
- (CGFloat)rowMargin
{
if ([self.delegate respondsToSelector:@selector(rowMarginInWaterflowLayout:)]) {
return [self.delegate rowMarginInWaterflowLayout:self];
} else {
return LYFDefaultRowMargin;
}
}
- (CGFloat)columnMargin
{
if ([self.delegate respondsToSelector:@selector(columnMarginInWaterflowLayout:)]) {
return [self.delegate columnMarginInWaterflowLayout:self];
} else {
return LYFDefaultColumnMargin;
}
}
- (NSInteger)columnCount
{
if ([self.delegate respondsToSelector:@selector(columnCountInWaterflowLayout:)]) {
return [self.delegate columnCountInWaterflowLayout:self];
} else {
return LYFDefaultColumnCount;
}
}
- (UIEdgeInsets)edgeInsets
{
if ([self.delegate respondsToSelector:@selector(edgeInsetsInWaterflowLayout:)]) {
return [self.delegate edgeInsetsInWaterflowLayout:self];
} else {
return LYFDefaultEdgeInsets;
}
}
#pragma mark - 懒加载
- (NSMutableArray *)columnHeights
{
if (!_columnHeights) {
_columnHeights = [NSMutableArray array];
}
return _columnHeights;
}
- (NSMutableArray *)attrsArray
{
if (!_attrsArray) {
_attrsArray = [NSMutableArray array];
}
return _attrsArray;
}
/**
* 初始化
*/
- (void)prepareLayout
{
[super prepareLayout];
self.contentHeight = 0;
// 清除以前计算的所有高度
[self.columnHeights removeAllObjects];
for (NSInteger i = 0; i < self.columnCount; i++) {
[self.columnHeights addObject:@(self.edgeInsets.top)];
}
// 清除之前所有的布局属性
[self.attrsArray removeAllObjects];
// 开始创建每一个cell对应的布局属性
NSInteger count = [self.collectionView numberOfItemsInSection:0];
for (NSInteger i = 0; i < count; i++) {
// 创建位置
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
// 获取indexPath位置cell对应的布局属性
UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:indexPath];
[self.attrsArray addObject:attrs];
}
}
/**
* 决定cell的排布
*/
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
return self.attrsArray;
}
/**
* 返回indexPath位置cell对应的布局属性
*/
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
// 创建布局属性
UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
// collectionView的宽度
CGFloat collectionViewW = self.collectionView.frame.size.width;
// 设置布局属性的frame
CGFloat w = (collectionViewW - self.edgeInsets.left - self.edgeInsets.right - (self.columnCount - 1) * self.columnMargin) / self.columnCount;
CGFloat h = [self.delegate waterflowLayout:self heightForItemAtIndex:indexPath.item itemWidth:w];
// 找出高度最短的那一列
NSInteger destColumn = 0;
CGFloat minColumnHeight = [self.columnHeights[0] doubleValue];
for (NSInteger i = 1; i < self.columnCount; i++) {
// 取得第i列的高度
CGFloat columnHeight = [self.columnHeights[i] doubleValue];
if (minColumnHeight > columnHeight) {
minColumnHeight = columnHeight;
destColumn = i;
}
}
CGFloat x = self.edgeInsets.left + destColumn * (w + self.columnMargin);
CGFloat y = minColumnHeight;
if (y != self.edgeInsets.top) {
y += self.rowMargin;
}
attrs.frame = CGRectMake(x, y, w, h);
// 更新最短那列的高度
self.columnHeights[destColumn] = @(CGRectGetMaxY(attrs.frame));
// 记录内容的高度
CGFloat columnHeight = [self.columnHeights[destColumn] doubleValue];
if (self.contentHeight < columnHeight) {
self.contentHeight = columnHeight;
}
return attrs;
}
- (CGSize)collectionViewContentSize
{
return CGSizeMake(0, self.contentHeight + self.edgeInsets.bottom);
}
具体使用如下：
LYFWaterflowLayout *layout = [[LYFWaterflowLayout alloc]init];
layout.delegate =self;
UICollectionView *collectionView = [[UICollectionView alloc]initWithFrame:self.view.bounds collectionViewLayout:layout];
cell高度设置(必须实现的代理)
- (CGFloat)waterflowLayout:(LYFWaterflowLayout *)waterflowLayout heightForItemAtIndex:(NSUInteger)index itemWidth:(CGFloat)itemWidth
{
return self.view.frame.size.height / 3;
}
设置行数或列数（默认为3）
- (CGFloat)columnCountInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout
{
return 4;
}
设置列间距（默认为10）
- (CGFloat)columnMarginInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout
{
return 20;
}
设置行间距（默认为10）
- (CGFloat)rowMarginInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout
{
return 20;
}
设置内边距（默认为10,10,10,10）
- (UIEdgeInsets)edgeInsetsInWaterflowLayout:(LYFWaterflowLayout *)waterflowLayout
{
return UIEdgeInsetsMake(20, 20, 20, 20);
}
