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
#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
#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;
#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, 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, 10);#endif return [layout autorelease];}- (void)changeLayout:(WaterfallFlowLayout *)layout { layout.numberOfColumns = 3;}- (void)createCollectionView { CGRect frame = CGRectMake(0, 20, 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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