轮播图的无限轮播

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, 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, imageY, imageW,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];