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

已经封装为一个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。

#import@interface ESPicPageView : UIView

@property (nonatomic, strong) NSArray *images;

@end

// --------------------------------------------

#import "ESPicPageView.h"

#import "UIImageView+WebCache.h"

@interface ESPicPageView ()

@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

网址:http://blog.csdn.net/xyt8023y/article/details/50116571

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