一行iOS代码实现图片无限轮播器

2020-07-26 02:48:36

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最近一直在找实现图片无限轮播的方法，在网上也看了不少方法，大都不太合适，最终看到某IT培训公司一位讲师用

UICollectionView：一行代码实现图片无限轮播器的方法，当然想一行代码实现轮播功能，前期还是有一些工作要做。下面就把这个方法分享给大家！

一、图片无限轮播实现效果图：

图片无限轮播.gif

二、实现原理与分析：

假设有三张图片0、1、2，想要实现无限轮播，我们可以将UICollectionView的cell个数设为图片的个数 x 3，也就是把三张图片重复添加到9个cell中，可以把无限轮播分解成五种特殊的状态（五个临界点），轮播开始时为初始状态，在定时器的作用下依次滚动到最后一个cell，此时为右临界状态显示的是第2张图片，若想继续无缝滚动到第0图片，我们可以偷偷的将collectionView滚动到第三个cell上，可以看第四幅转态图此时显示的依然是第2张图片，这样再次滚动就是第0张图，这样就实现了cell向左滚动的无限循环轮播；向右滚动的原理一样，就是第三幅图到第五幅图的变化。

初始界状态.png

右临界状态.png

左临界状态.png

Paste_Image.png

三、代码：

类文件.png

JFWeakTimerTargetObject继承自NSObject
JFLoopView继承自UIView
JFLoopViewCell继承自UICollectionViewCell
JFLoopViewLayout继承自UICollectionViewFlowLayout
JFMainViewController继承自UIViewController

JFWeakTimerTargetObject重写定时器NSTimer的+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;类方法的目的是：避免当定时器强引用JFLoopView类，JFLoopView无法被释放的问题。

JFWeakTimerTargetObject.h文件

#import <Foundation/Foundation.h>@interface JFWeakTimerTargetObject : NSObject+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo;@end

JFWeakTimerTargetObject.m文件

#import "JFWeakTimerTargetObject.h"@interface JFWeakTimerTargetObject ()@property (nonatomic, weak) id target;@property (nonatomic, assign) SEL selector;@end@implementation JFWeakTimerTargetObject+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)ti target:(id)aTarget selector:(SEL)aSelector userInfo:(nullable id)userInfo repeats:(BOOL)yesOrNo { //创建当前类对象 JFWeakTimerTargetObject *object = [[JFWeakTimerTargetObject alloc] init]; object.target = aTarget; object.selector = aSelector; return [NSTimer scheduledTimerWithTimeInterval:ti target:object selector:@selector(fire:) userInfo:userInfo repeats:yesOrNo];}- (void)fire:(id)obj { [self.target performSelector:self.selector withObject:obj];}@end

JFLoopView.h文件

#import <UIKit/UIKit.h>@interface JFLoopView : UIView//JFLoopView初始化方法- (instancetype)initWithImageArray:(NSArray *)imageArray;@end

JFLoopView.m文件

#import "JFLoopView.h"#import "JFLoopViewLayout.h"#import "JFLoopViewCell.h"#import "JFWeakTimerTargetObject.h"@interface JFLoopView () <UICollectionViewDelegate, UICollectionViewDataSource>@property (nonatomic, strong) UICollectionView *collectionView;@property (nonatomic, strong) UIPageControl *pageControl;@property (nonatomic, strong) NSArray *imageArray;@property (nonatomic, weak) NSTimer *timer;@endstatic NSString *ID = @"loopViewCell";@implementation JFLoopView- (instancetype)initWithImageArray:(NSArray *)imageArray { if (self = [super init]) { UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:[[JFLoopViewLayout alloc] init]]; [collectionView registerClass:[JFLoopViewCell class] forCellWithReuseIdentifier:ID]; collectionView.dataSource = self; collectionView.delegate = self; [self addSubview:collectionView]; self.collectionView = collectionView; self.imageArray = imageArray; //添加分页器 [self addSubview:self.pageControl]; //回到主线程刷新UI dispatch_async(dispatch_get_main_queue(), ^{ //设置滚动的初始状态在 [self.collectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForItem:self.imageArray.count inSection:0] atScrollPosition:UICollectionViewScrollPositionLeft animated:NO]; //添加定时器 [self addTimer]; }); } return self;}/// 懒加载pageControl- (UIPageControl *)pageControl { if (!_pageControl) { _pageControl = [[UIPageControl alloc] initWithFrame:CGRectMake(0, 220, 0, 30)]; _pageControl.numberOfPages = self.imageArray.count; _pageControl.pageIndicatorTintColor = [UIColor orangeColor]; _pageControl.currentPageIndicatorTintColor = [UIColor purpleColor]; } return _pageControl;}#pragma mark --- UICollectionViewDataSource 数据源方法- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section { return self.imageArray.count * 3;}- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { JFLoopViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:ID forIndexPath:indexPath]; cell.imageName = self.imageArray[indexPath.item % self.imageArray.count]; return cell;}#pragma mark ---- UICollectionViewDelegate/// 滚动完毕就会调用（如果不是人为拖拽scrollView导致滚动完毕，才会调用这个方法）- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView { [self scrollViewDidEndDecelerating:scrollView];}/// 当滚动减速时调用- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView { CGFloat offsetX = scrollView.contentOffset.x; NSInteger page = offsetX / scrollView.bounds.size.width; //手动滚动到左边临界状态 if (page == 0) { page = self.imageArray.count; self.collectionView.contentOffset = CGPointMake(page * scrollView.frame.size.width, 0); //滚动到右临界状态 }else if (page == [self.collectionView numberOfItemsInSection:0] - 1) { page = self.imageArray.count - 1; self.collectionView.contentOffset = CGPointMake(page * scrollView.frame.size.width, 0); } //设置UIPageControl当前页 NSInteger currentPage = page % self.imageArray.count; self.pageControl.currentPage =currentPage; //添加定时器 [self addTimer];}///手指开始拖动时调用- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView { //移除定时器 [self removeTimer];}/// 添加定时器- (void)addTimer { if (self.timer) return; self.timer = [JFWeakTimerTargetObject scheduledTimerWithTimeInterval:1.5 target:self selector:@selector(nextImage) userInfo:nil repeats:YES]; [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];}/// 移除定时器- (void)removeTimer { [self.timer invalidate]; self.timer = nil;}/// 切换到下一张图片- (void)nextImage { CGFloat offsetX = self.collectionView.contentOffset.x; NSInteger page = offsetX / self.collectionView.bounds.size.width; [self.collectionView setContentOffset:CGPointMake((page + 1) * self.collectionView.bounds.size.width, 0) animated:YES];}- (void)layoutSubviews { [super layoutSubviews]; self.collectionView.frame = self.bounds;}- (void)dealloc { [self removeTimer];}@end

JFLoopViewCell.h文件

#import <UIKit/UIKit.h>@interface JFLoopViewCell : UICollectionViewCell@property (nonatomic, copy) NSString *imageName;@end

JFLoopViewCell.m文件

#import "JFLoopViewCell.h"@interface JFLoopViewCell ()@property (nonatomic, weak) UIImageView *iconView;@end@implementation JFLoopViewCell- (instancetype)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { UIImageView *iconView = [[UIImageView alloc] init]; [self addSubview:iconView]; self.iconView = iconView; } return self;}- (void)setImageName:(NSString *)imageName { _imageName = imageName; self.iconView.image = [UIImage imageNamed:imageName];}- (void)layoutSubviews { [super layoutSubviews]; self.iconView.frame = self.bounds;}@end

JFLoopViewLayout.h文件

#import <UIKit/UIKit.h>@interface JFLoopViewLayout : UICollectionViewFlowLayout@end

JFLoopViewLayout.m文件

#import "JFLoopViewLayout.h"@implementation JFLoopViewLayout/// 准备布局- (void)prepareLayout { [super prepareLayout]; //设置item尺寸 self.itemSize = self.collectionView.frame.size; //设置滚动方向 self.scrollDirection = UICollectionViewScrollDirectionHorizontal; //设置分页 self.collectionView.pagingEnabled = YES; //设置最小间距 self.minimumLineSpacing = 0; self.minimumInteritemSpacing = 0; //隐藏水平滚动条 self.collectionView.showsHorizontalScrollIndicator = NO;}@end

JFMainViewController.h文件

#import <UIKit/UIKit.h>@interface JFMainViewController : UIViewController@end

JFMainViewController.m文件

#import "JFMainViewController.h"#import "JFLoopView.h"@interface JFMainViewController ()@property (nonatomic, strong) JFLoopView *loopView;@end@implementation JFMainViewController- (void)viewDidLoad { [super viewDidLoad]; //关闭自动调整滚动视图 self.automaticallyAdjustsScrollViewInsets = NO;}- (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; self.navigationController.navigationBar.hidden = YES;}- (void)loadView { [super loadView]; //设置图片数据 NSArray *imageArray = @[@"srcoll_01",@"srcoll_02",@"srcoll_03"]; //此行代码实现无限轮播 _loopView = [[JFLoopView alloc] initWithImageArray:imageArray]; //设置loopView的frame _loopView.frame = CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, 250); [self.view addSubview:self.loopView];}- (void)didReceiveMemoryWarning { [super didReceiveMemoryWarning]; // Dispose of any resources that can be recreated.}@end

注意：如果你的控制器有UINavigationBar，且隐藏了navigationBar，一定要记得设置self.automaticallyAdjustsScrollViewInsets = NO; automaticallyAdjustsScrollViewInsets是干嘛的呢？简单点说就是automaticallyAdjustsScrollViewInsets根据所在界面的status bar、navigationbar、与tabbar的高度，自动调整scrollview的 inset,设置为NO，不让viewController调整，我们自己修改布局即可。如果不设置为NO就可能出现下面的情况，自动滚动和拖动的时候imageView的位置会变化。

图片无限轮播bug展示.gif

四、总结：

1、实现无限轮播器的主要控件是UICollectionView和UIPageControl,
2、封装好工具类以后再使用时一行_loopView = [[JFLoopView alloc] initWithImageArray:imageArray];代码，然后设置frame就可以复用无限轮播器。
3、合理切换图片和图片排列的方法，加上恰当地使用UICollectionView提供的代理方法就可以完美的实现无限轮播器。

写在最后：

下一篇文章讲用UICollectionView实现电商APP首页的方法：

电商APP的首页展示.gif