IOS开发之UIScrollView实现图片轮播器的无限滚动
简介
在现在的一些App中常常见到图片轮播器,一般用于展示广告、新闻等数据,在iOS内并没有现成的控件直接实现这种功能,但是通过UIScrollView的允许分页设置,可以实现滚动轮播的功能。
轮播原理
UIScrollView对象有pagingEnable成员,如果设置为YES,那么每一个scrollView尺寸这么大的区域就会被当作一页,在滚动时会根据滚动的比例自动计算应该切换到哪一页。
无限滚动原理
要实现无限滚动,需要额外的两张图片,假设我们的图片有五张,存在images数组中,那么我们在将图片插入到scrollView中时,在第一张图片前面插入一个最后一张图片作为辅助图片,在最后一张后面插入一个第一张图片作为辅助图片。这样,当滚动到第一张前面一张时,在页面切换结束后无动画的切换scrollView的偏移量为最后一张图片(不包含最后一张后面的第一张那个辅助图片),这样就实现了由辅助图片到真实图片的过渡,之所以设置辅助图片是为了在滚动中看到那个真实图片。同理,当滚动到最后一张的后面一张时,我们吧scrollView的偏移量设置为第一张图片即可。
具体的代码实现
这个代码是在开发一个项目中所写的,已经封装称一个View,只需要调用initWithFrame指定轮播器尺寸,然后通过设置images成员的值即可实现无限滚动的轮播。
// .h // // ESPicPageView.h // 享技 // // Created by 11 on 11/30/15. // Copyright © 2015 soulghost. All rights reserved. // #import <UIKit/UIKit.h> @interface ESPicPageView : UIView @property (nonatomic,strong) NSArray *images; @end // -------------------------------------------- // .m // // ESPicPageView.m // 享技 // // Created by 11 on 11/30/15. // Copyright © 2015 soulghost. All rights reserved. // #import "ESPicPageView.h" #import "UIImageView+WebCache.h" @interface ESPicPageView () <UIScrollViewDelegate> @property (nonatomic,weak) UIScrollView *scrollView; @property (nonatomic,weak) UIPageControl *pageControl; @property (nonatomic,assign) CGFloat imgW; @property (nonatomic,assign) CGFloat imgH; @property (nonatomic,strong) NSTimer *timer; @property (nonatomic,strong) NSArray *imageViews; @property (nonatomic,assign) NSInteger imageCount; @end @implementation ESPicPageView - (instancetype)initWithFrame:(CGRect)frame{ if (self = [super initWithFrame:frame]) { self.backgroundColor = [UIColor blueColor]; UIScrollView *scrollView = [[UIScrollView alloc] init]; self.scrollView = scrollView; self.scrollView.delegate = self; self.scrollView.pagingEnabled = YES; self.scrollView.showsHorizontalScrollIndicator = NO; self.scrollView.backgroundColor = [UIColor whiteColor]; [self addSubview:scrollView]; self.imgW = frame.size.width; self.imgH = frame.size.height; [self setNeedsLayout]; UIPageControl *pageControl = [[UIPageControl alloc] initWithFrame:CGRectMake(frame.size.width - 50,frame.size.height - 10,0)]; self.pageControl = pageControl; self.pageControl.numberOfPages = 1; [self addSubview:pageControl]; self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(nextImage) userInfo:nil repeats:YES]; [[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes]; } return self; } - (void)nextImage{ NSInteger page = self.pageControl.currentPage; page = self.pageControl.currentPage + 1; CGPoint offset = CGPointMake((1 + page) * self.imgW,0); [self.scrollView setContentOffset:offset animated:YES]; } - (void)setupImageViews{ for (int i = 0; i < self.images.count + 2; i++) { UIImageView *imageView = [[UIImageView alloc] init]; CGFloat imageX = i * self.imgW; CGFloat imageY = 0; CGFloat imageW = self.imgW; CGFloat imageH = self.imgH; imageView.frame = CGRectMake(imageX,imageY,imageW,imageH); [self.scrollView insertSubview:imageView atIndex:0]; } } - (NSArray *)imageViews{ if (_imageViews == nil) { NSMutableArray *arr = [NSMutableArray array]; for (int i = 0; i < self.images.count + 2; i++) { UIImageView *imageView = [[UIImageView alloc] init]; CGFloat imageX = i * self.imgW; CGFloat imageY = 0; CGFloat imageW = self.imgW; CGFloat imageH = self.imgH; imageView.frame = CGRectMake(imageX,imageH); [self.scrollView insertSubview:imageView atIndex:0]; [arr addObject:imageView]; } _imageViews = arr; } return _imageViews; } - (void)setImages:(NSArray *)images{ _images = images; self.imageCount = images.count; self.pageControl.numberOfPages = self.imageCount; [self addPics]; } - (void)addPics{ for (int i = 0; i < self.images.count + 2; i++) { UIImageView *imageView = self.imageViews[i]; if (i == 0) { imageView.image = [self.images lastObject]; }else if(i == self.images.count + 1){ imageView.image = [self.images firstObject]; }else{ imageView.image = self.images[i - 1]; } } } - (void)layoutSubviews{ [super layoutSubviews]; self.scrollView.frame = self.bounds; self.scrollView.contentSize = CGSizeMake((self.imageCount + 2) * self.imgW,0); [self.scrollView setContentOffset:CGPointMake(self.imgW,0) animated:NO]; } - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{ [self.timer invalidate]; self.timer = nil; } - (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{ self.timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(nextImage) userInfo:nil repeats:YES]; [[NSRunLoop currentRunLoop ] addTimer:self.timer forMode:NSRunLoopCommonModes]; } - (void)scrollViewDidScroll:(UIScrollView *)scrollView{ if (scrollView.contentOffset.x == self.imgW * (self.imageCount + 1)) { [self.scrollView setContentOffset:CGPointMake(self.imgW,0) animated:NO]; }else if(scrollView.contentOffset.x == 0){ [self.scrollView setContentOffset:CGPointMake(self.imgW * (self.imageCount),0) animated:NO]; } self.pageControl.currentPage = (self.scrollView.contentOffset.x + self.imgW * 0.5f) / self.imgW - 1; } @end
以上就是使用UIScrollView实现图片的轮播的功能,如有疑问大家可以留言,也可以到本站社区留言讨论,感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!