瀑布流现在是一些APP常用的场景，如电子商城、旅游、社区等。实现起来很简单。
项目github下载地址
WaterfallCollectionViewCell
先定义一个带XIB的WaterfallCollectionViewCell
#import <UIKit/UIKit.h>
@interface WaterfallCollectionViewCell : UICollectionViewCell
@property (nonatomic,weak)IBOutlet UIImageView *image;
@end
XIB部分推荐运用AutoLayout进行布局，可以节省好多时间。
XIB
WaterfallCollectionViewLayout
定义WaterfallCollectionViewLayout集成自UICollectionViewLayout，这里的思路是：
- 实现瀑布流
- 需要根据要现实的内容计算每个Item的高度？
- 每个Item的上下左右边距是多少？
- 瀑布流要现实多少列？
那么问题来了要怎么去实现呢？这里需要运用到代理，一直有一些初学者对代理这个东西用起来感觉有点绕，其实可以这么理解。 - 我是一个CollectionViewController
- 我想要计算每个Item的宽高？
- 我想要计算下一个Item要进行布局时，放在哪个列的下面？
- 但这个事情我做不合适，为什么呢？
- 因为我是一个大领导有好多事情要管，你们每个Item自己管好了，我给你们提供一个沟通渠道（代理实现的方法）告诉你们我想要什么就行，那么剩下的事情就委托给你们自己了。
#import <UIKit/UIKit.h>
@class WaterfallCollectionViewLayout;
@protocol WaterfallCollectionViewDelegate <NSObject>
@required
- (CGFloat)waterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout heightForItemAtIndex:(NSUInteger)index itemWidth:(CGFloat)itemWidth;
@optional
- (NSInteger)columnCountInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout;
- (CGFloat)columnMarginInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout;
- (CGFloat)rowMarginInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout;
- (UIEdgeInsets)edgeInsetsInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout;
@end
@interface WaterfallCollectionViewLayout : UICollectionViewLayout
@property (nonatomic, weak) id<WaterfallCollectionViewDelegate> delegate;
@end
//
// WaterfallCollectionViewLayout.m
// UICollectionVIewDemo
//
// Created by DaLei on 2017/6/8.
// Copyright © 2017年 DaLei. All rights reserved.
//
#import "WaterfallCollectionViewLayout.h"
/** 默认的列数 */
static const NSInteger DefaultColumnCount = 3;
/** 每一列之间的间距 */
static const CGFloat DefaultColumnMargin = 10;
/** 每一行之间的间距 */
static const CGFloat DefaultRowMargin = 10;
/** 边缘间距 */
static const UIEdgeInsets DefaultEdgeInsets = {10, 10, 10, 10};
@interface WaterfallCollectionViewLayout()
/** 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 WaterfallCollectionViewLayout
#pragma mark - 常见数据处理
- (CGFloat)rowMargin {
if ([self.delegate respondsToSelector:@selector(rowMarginInWaterflowLayout:)]) {
return [self.delegate rowMarginInWaterflowLayout:self];
} else {
return DefaultRowMargin;
}
}
- (CGFloat)columnMargin {
if ([self.delegate respondsToSelector:@selector(columnMarginInWaterflowLayout:)]) {
return [self.delegate columnMarginInWaterflowLayout:self];
} else {
return DefaultColumnMargin;
}
}
- (NSInteger)columnCount {
if ([self.delegate respondsToSelector:@selector(columnCountInWaterflowLayout:)]) {
return [self.delegate columnCountInWaterflowLayout:self];
} else {
return DefaultColumnCount;
}
}
- (UIEdgeInsets)edgeInsets {
if ([self.delegate respondsToSelector:@selector(edgeInsetsInWaterflowLayout:)]) {
return [self.delegate edgeInsetsInWaterflowLayout:self];
} else {
return DefaultEdgeInsets;
}
}
#pragma mark - 懒加载
- (NSMutableArray *)columnHeights {
if (!_columnHeights) {
_columnHeights = [NSMutableArray array];
}
return _columnHeights;
}
- (NSMutableArray *)attrsArray {
if (!_attrsArray) {
_attrsArray = [NSMutableArray array];
}
return _attrsArray;
}
- (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);
}
@end
WaterfallCollectionViewController
新建WaterfallCollectionViewController，像普通的CollectionViewController一样进行定义即可，并且实现WaterfallCollectionViewDelegate告诉Item需要现实几列，每隔Item有多高，每个Item的边距是多少。
//
// WaterfallCollectionViewController.m
// UICollectionVIewDemo
//
// Created by DaLei on 2017/6/8.
// Copyright © 2017年 DaLei. All rights reserved.
//
#import "WaterfallCollectionViewController.h"
#import "WaterfallCollectionViewCell.h"
#import "WaterfallCollectionViewLayout.h"
#define RGBColor(r, g, b) [UIColor colorWithRed:(r)/255.0 green:(g)/255.0 blue:(b)/255.0 alpha:1.0]
#define RandomRGBColor RGBColor(arc4random_uniform(255), arc4random_uniform(255), arc4random_uniform(255))
@interface WaterfallCollectionViewController ()<WaterfallCollectionViewDelegate>
@property(nonatomic,strong)NSArray *productArray;
@end
@implementation WaterfallCollectionViewController
static NSString * const reuseIdentifier = @"WaterfallCollectionViewCell";
-(instancetype)init{
WaterfallCollectionViewLayout *layout = [WaterfallCollectionViewLayout new];
layout.delegate = self;
return [super initWithCollectionViewLayout:layout];
}
- (void)viewDidLoad {
[super viewDidLoad];
self.title = @"面皮大师-瀑布流";
// Register cell classes
[self.collectionView registerNib:[UINib nibWithNibName:NSStringFromClass([WaterfallCollectionViewCell class]) bundle:nil] forCellWithReuseIdentifier:reuseIdentifier];
self.collectionView.backgroundColor = RGBColor(235, 235, 235);
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
-(NSArray *)productArray{
if (!_productArray) {
_productArray = @[@"cell1",@"cell2",@"cell3",@"cell4",@"cell5",@"cell6",@"cell7",@"cell1",@"cell2",@"cell3",@"cell4",@"cell5",@"cell6",@"cell7",@"cell1",@"cell2",@"cell3",@"cell4",@"cell5",@"cell6",@"cell7"];
}
return _productArray;
}
#pragma mark <UICollectionViewDataSource>
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return [self.productArray count];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
WaterfallCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];
cell.backgroundColor = RandomRGBColor;
UIImage *image = [UIImage imageNamed:[self.productArray objectAtIndex:indexPath.item]];
[cell.image setImage:image];
return cell;
}
#pragma mark <WaterfallCollectionViewDelegate>
- (CGFloat)waterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout heightForItemAtIndex:(NSUInteger)index itemWidth:(CGFloat)itemWidth{
// 获取图片的宽高，根据图片的比例计算Item的高度。
UIImage *image = [UIImage imageNamed:[self.productArray objectAtIndex:index]];
CGFloat fixelW = CGImageGetWidth(image.CGImage);
CGFloat fixelH = CGImageGetHeight(image.CGImage);
CGFloat itemHeight = fixelH * itemWidth / fixelW;
return itemHeight + 50;
}
- (NSInteger)columnCountInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout{
return 2;
}
- (CGFloat)columnMarginInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout{
return 10;
}
- (CGFloat)rowMarginInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout{
return 10;
}
- (UIEdgeInsets)edgeInsetsInWaterflowLayout:(WaterfallCollectionViewLayout *)waterflowLayout{
return UIEdgeInsetsMake(10, 10, 10, 10);
}
@end
运行效果：
瀑布流
学习参考：Developer_CYX
UICollectionViewController基础（1）
UICollectionViewController基础（2）引导页
UICollectionViewController基础（3）瀑布流
UICollectionViewController基础（4）自定义
