在网上找了许久，一直没有发现有提供横向瀑布流效果的。在项目中用到了我就在垂直瀑布流的基础上，进行了修改，做出了横向瀑布流的效果。同时也对一些UICollectionView的属性进行简单的注释，方便以后查阅。

1、首先要写一个继承与NSObject的布局类，记录每一行（列）目前的宽度（高度）。再添加一个新的cell的时候进行判断比较，添加到最短的那一行或一列上。

2、横向的布局类入下，垂直的话就是讲对应的X Y轴数据进行调整即可。
WaterfallFlowLayout为布局类，继承与NSObject。.h文件入下

@H_301_7@ #import <UIKit/UIKit.h> // 类的前置声明 @class WaterfallFlowLayout; @protocol WaterfallFlowLayoutDelegate <NSObject> // 动态获取 item 宽度 - (CGFloat) WaterfallFlowLayout:(WaterfallFlowLayout *) layout widthForItemAtIndexPath:(NSIndexPath *) indexPath; @end @interface WaterfallFlowLayout : UICollectionViewLayout @property (nonatomic,assign) id <WaterfallFlowLayoutDelegate> delegate; @property (nonatomic) NSInteger numberOfColumns; @property (nonatomic) CGFloat minimumLineSpacing; @property (nonatomic) CGFloat minimumInteritemSpacing; @property (nonatomic) UIEdgeInsets sectionInset; @end

WaterfallFlowLayout为布局类，继承与NSObject。.m文件入下

@H_301_7@ #import "WaterfallFlowLayout.h" @interface WaterfallFlowLayout () { // 用于记录每一列布局到的宽度 NSMutableArray * _widthOfColumns; // 用于保存所有item的属性 (frame) NSMutableArray * _itemsAttributes; } @end @implementation WaterfallFlowLayout - (void) setNumberOfColumns:(NSInteger)numberOfColumns { if (_numberOfColumns != numberOfColumns) { _numberOfColumns = numberOfColumns; // 让原有布局失效，需要重新布局 [self invalidateLayout]; } } - (void)setMinimumLineSpacing:(CGFloat)minimumLineSpacing { if (_minimumLineSpacing != minimumLineSpacing) { _minimumLineSpacing = minimumLineSpacing; [self invalidateLayout]; } } - (void)setMinimumInteritemSpacing:(CGFloat)minimumInteritemSpacing { if (_minimumInteritemSpacing != minimumInteritemSpacing) { _minimumInteritemSpacing = minimumInteritemSpacing; [self invalidateLayout]; } } - (void)setSectionInset:(UIEdgeInsets)sectionInset { if (!UIEdgeInsetsEqualToEdgeInsets(_sectionInset,sectionInset)) { _sectionInset = sectionInset; [self invalidateLayout]; } } //重写方法 1: 准备布局 -(void)prepareLayout { [super prepareLayout]; // 真正的布局在这里完成 if (_itemsAttributes) { [_itemsAttributes removeAllObjects]; }else { _itemsAttributes = [[NSMutableArray alloc] init]; } if (_widthOfColumns) { [_widthOfColumns removeAllObjects]; }else { _widthOfColumns = [[NSMutableArray alloc] init]; } for (NSInteger i = 0; i < self.numberOfColumns; i++) { // 初始化每一列的宽度(默认为上边距) // _heightOfColumns[i] = @(self.sectionInset.top); [_widthOfColumns addObject:@(self.sectionInset.left)]; } // item的总数 NSInteger count = [self.collectionView numberOfItemsInSection:0]; // CGFloat itemWidth = (self.collectionView.frame.size.width - self.sectionInset.left - self.sectionInset.right - (_numberOfColumns-1) * _minimumInteritemSpacing )/_numberOfColumns; // 总的高度 (集合视图的宽度) CGFloat totalHeight = self.collectionView.frame.size.height; // 有效的高度 (出去间隔及边界) CGFloat validHeight = totalHeight - self.sectionInset.top - self.self.sectionInset.bottom - (self.numberOfColumns-1) * self.minimumInteritemSpacing; // 每一个item的高度 CGFloat itemHeight = validHeight/self.numberOfColumns; // 设置item的默认宽度 CGFloat itemWidth = itemHeight; for (NSInteger i = 0; i<count; i++) { // 最短列的下标 NSInteger index = [self indexOfShortestColumn]; CGFloat originY = self.sectionInset.top + index * (itemHeight +self.minimumInteritemSpacing); CGFloat originX = [_widthOfColumns[index] floatValue]; // 构造 indexPath NSIndexPath * indexPath = [NSIndexPath indexPathForItem:i inSection:0]; // 动态的获取宽度 if ([self.delegate respondsToSelector:@selector(WaterfallFlowLayout:widthForItemAtIndexPath:)]) { itemWidth = [self.delegate WaterfallFlowLayout:self widthForItemAtIndexPath:indexPath]; } UICollectionViewLayoutAttributes * attr = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath]; attr.frame = CGRectMake(originX,originY,itemWidth,itemHeight); // 保存 item 的属性 到数组中 [_itemsAttributes addObject:attr]; // 更新布局到的一列(最短列) 的高度 _widthOfColumns[index] = @(originX + itemWidth + self.minimumLineSpacing); } // 刷新显示 [self.collectionView reloadData]; } //重写方法 2: 返回指定区域的item的属性(frame) - (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect { NSMutableArray * array = [NSMutableArray array]; for (UICollectionViewLayoutAttributes * attr in _itemsAttributes) { // 判断两个矩形是否有交集 if (CGRectIntersectsRect(attr.frame,rect)) { [array addObject:attr]; } } return array; } //重写方法 3: 返回内容的尺寸 -(CGSize)collectionViewContentSize { CGFloat height = self.collectionView.frame.size.height; NSInteger index = [self indexOfLongestColumn]; CGFloat width = [_widthOfColumns[index] floatValue] + self.sectionInset.right - self.minimumLineSpacing; return CGSizeMake(width,height); } - (NSInteger) indexOfLongestColumn { NSInteger index = 0; for (NSInteger i = 0; i<_numberOfColumns; i++) { if ([_widthOfColumns[i] floatValue] > [_widthOfColumns[index] floatValue]) { index = i; } } return index; } - (NSInteger) indexOfShortestColumn { NSInteger index = 0; for (NSInteger i = 0; i<_numberOfColumns; i++) { if ([_widthOfColumns[i] floatValue] < [_widthOfColumns[index] floatValue]) { index = i; } } return index; } @end

3、上边的这个布局类可以直接复制粘贴下来。然后就是创建你的UICollectionView

在collectionView的cell中可以直接创建imageView或者是label添加到cell上，用来显示数据。
collectionView默认section缩进左右是0
调节横向cell间距
layout.minimumLineSpacing = 10;
调节纵向cell间距
layout.minimumInteritemSpacing = 20;
调节瀑布流显示的行数，当然了你的collectionView的高（宽）足够显示几行（列）就会自动显示多上行（列）；
layout.numberOfColumns = 3;

@H_301_7@ #import "RootViewController.h" #import "WaterfallFlowLayout.h" @interface RootViewController () <UICollectionViewDataSource,UICollectionViewDelegateFlowLayout,WaterfallFlowLayoutDelegate> { UICollectionView * _collectionView; } @end @implementation RootViewController - (void)dealloc { [_collectionView release]; [super dealloc]; } - (void)viewDidLoad { [super viewDidLoad]; // 创建集合视图 [self createCollectionView]; } - (UICollectionViewLayout *)createLayout { #if 1 WaterfallFlowLayout * layout = [[WaterfallFlowLayout alloc] init]; layout.sectionInset = UIEdgeInsetsMake(20,20,20); layout.minimumLineSpacing = 10; layout.minimumInteritemSpacing = 20; layout.numberOfColumns = 3; layout.delegate = self; [self performSelector:@selector(changeLayout:) withObject:layout afterDelay:3]; #else UICollectionViewFlowLayout * layout = [[UICollectionViewFlowLayout alloc] init]; layout.minimumLineSpacing = 10; layout.itemSize = CGSizeMake(150,100); layout.sectionInset = UIEdgeInsetsMake(10,10,10); #endif return [layout autorelease]; } - (void)changeLayout:(WaterfallFlowLayout *)layout { layout.numberOfColumns = 3; } - (void)createCollectionView { CGRect frame = CGRectMake(0,VIEW_WIDTH,VIEW_HEIGHT-20); _collectionView = [[UICollectionView alloc] initWithFrame:frame collectionViewLayout:[self createLayout]]; _collectionView.backgroundColor = [UIColor cyanColor]; // 设置代理 _collectionView.delegate = self; _collectionView.dataSource = self; // 注册cell 类型 及 复用标识 [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cellId"]; [self.view addSubview:_collectionView]; } #pragma mark - UICollectionViewDataSource - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section { return 102; } - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { UICollectionViewCell * cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cellId" forIndexPath:indexPath]; UILabel * label = nil; NSArray * array = cell.contentView.subviews; if (array.count) { label = array[0]; }else { label = [[UILabel alloc] init]; // label.frame = cell.bounds; label.textAlignment = NSTextAlignmentCenter; label.font = [UIFont systemFontOfSize:50]; [cell.contentView addSubview:label]; [label release]; } label.frame = cell.bounds; label.text = [NSString stringWithFormat:@"%ld",indexPath.item]; label.textColor = [UIColor whiteColor]; cell.backgroundColor = RandomColor; return cell; } - (CGSize) collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath { return CGSizeMake( arc4random()%100+200,110); } -(CGFloat) WaterfallFlowLayout:(WaterfallFlowLayout *)layout widthForItemAtIndexPath:(NSIndexPath *)indexPath{ return arc4random()%150+50; } -(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{ NSLog(@"点击了第 %ld 组，第 %ld 行",indexPath.section,indexPath.row); } - (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; } @end

实现的效果如下

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