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];
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