IOS开发之UIScrollView实现图片轮播器的无限滚动

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！

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