使用UIScrollView 结合 UIImageView 实现图片循环滚动

场景：

在开发工作中，有时我们需要实现一组图片循环滚动的情况。当我们使用 UIScrollView 结合 UIImageView 来实现时，一般 UIImageView 会尽量考虑重用，下面例子是以（左中右）三个 UIImageView 的使用，其实也可以考虑使用 两个 UIImageView 实现的情况。这样避免 一组图片多少个就对应多少个 UIImageView 所导致占用过多内存的情况。

效果如下：

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController <UIScrollViewDelegate>
@property (strong, nonatomic) UIScrollView *scrV;
@property (strong, nonatomic) UIPageControl *pageC;
@property (strong, nonatomic) UIImageView *imgVLeft;
@property (strong, nonatomic) UIImageView *imgVCenter;
@property (strong, nonatomic) UIImageView *imgVRight;
@property (strong, nonatomic) UILabel *lblImageDesc;
@property (strong, nonatomic) NSMutableDictionary *mDicImageData;
@property (assign, nonatomic) NSUInteger currentImageIndex;
@property (assign, nonatomic) NSUInteger imageCount;

@end

ViewController.m

#import "ViewController.h"

#define kWidthOfScreen [[UIScreen mainScreen] bounds].size.width
#define kHeightOfScreen [[UIScreen mainScreen] bounds].size.height
#define kImageViewCount 3
@interface ViewController ()
/**
 *  加载图片数据
 */
- (void)loadImageData;

/**
 *  添加滚动视图
 */
- (void)addScrollView;

/**
 *  添加三个图片视图到滚动视图内
 */
- (void)addImageViewsToScrollView;

/**
 *  添加分页控件
 */
- (void)addPageControl;

/**
 *  添加标签；用于图片描述
 */
- (void)addLabel;

/**
 *  根据当前图片索引设置信息
 *
 *  @param currentImageIndex 当前图片索引；即中间
 */
- (void)setInfoByCurrentImageIndex:(NSUInteger)currentImageIndex;

/**
 *  设置默认信息
 */
- (void)setDefaultInfo;

/**
 *  重新加载图片
 */
- (void)reloadImage;

- (void)layoutUI;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self layoutUI];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)loadImageData {
    NSString *path = [[NSBundle mainBundle] pathForResource:@"ImageInfo" ofType:@"plist"];
    _mDicImageData = [NSMutableDictionary dictionaryWithContentsOfFile:path];
    _imageCount = _mDicImageData.count;
}

- (void)addScrollView {
    _scrV = [[UIScrollView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    _scrV.contentSize = CGSizeMake(kWidthOfScreen * kImageViewCount, kHeightOfScreen);
    _scrV.contentOffset = CGPointMake(kWidthOfScreen, 0.0);
    _scrV.pagingEnabled = YES;
    _scrV.showsHorizontalScrollIndicator = NO;
    _scrV.delegate = self;
    [self.view addSubview:_scrV];
}

- (void)addImageViewsToScrollView {
    //图片视图；左边
    _imgVLeft = [[UIImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, kWidthOfScreen, kHeightOfScreen)];
    _imgVLeft.contentMode = UIViewContentModeScaleAspectFit;
    [_scrV addSubview:_imgVLeft];
    
    //图片视图；中间
    _imgVCenter = [[UIImageView alloc] initWithFrame:CGRectMake(kWidthOfScreen, 0.0, kWidthOfScreen, kHeightOfScreen)];
    _imgVCenter.contentMode = UIViewContentModeScaleAspectFit;
    [_scrV addSubview:_imgVCenter];
    
    //图片视图；右边
    _imgVRight = [[UIImageView alloc] initWithFrame:CGRectMake(kWidthOfScreen * 2.0, 0.0, kWidthOfScreen, kHeightOfScreen)];
    _imgVRight.contentMode = UIViewContentModeScaleAspectFit;
    [_scrV addSubview:_imgVRight];
}

- (void)addPageControl {
    _pageC = [UIPageControl new];
    CGSize size= [_pageC sizeForNumberOfPages:_imageCount]; //根据页数返回 UIPageControl 合适的大小
    _pageC.bounds = CGRectMake(0.0, 0.0, size.width, size.height);
    _pageC.center = CGPointMake(kWidthOfScreen / 2.0, kHeightOfScreen - 80.0);
    _pageC.numberOfPages = _imageCount;
    _pageC.pageIndicatorTintColor = [UIColor whiteColor];
    _pageC.currentPageIndicatorTintColor = [UIColor brownColor];
    _pageC.userInteractionEnabled = NO; //设置是否允许用户交互；默认值为 YES，当为 YES 时，针对点击控件区域左（当前页索引减一，最小为0）右（当前页索引加一，最大为总数减一），可以编写 UIControlEventValueChanged 的事件处理方法
    [self.view addSubview:_pageC];
}

- (void)addLabel {
    _lblImageDesc = [[UILabel alloc] initWithFrame:CGRectMake(0.0, 40.0, kWidthOfScreen, 40.0)];
    _lblImageDesc.textAlignment = NSTextAlignmentCenter;
    _lblImageDesc.textColor = [UIColor whiteColor];
    _lblImageDesc.font = [UIFont boldSystemFontOfSize:[UIFont labelFontSize]];
    _lblImageDesc.text = @"Fucking now.";
    [self.view addSubview:_lblImageDesc];
}

- (void)setInfoByCurrentImageIndex:(NSUInteger)currentImageIndex {
    NSString *currentImageNamed = [NSString stringWithFormat:@"%lu.png", (unsigned long)currentImageIndex];
    _imgVCenter.image = [UIImage imageNamed:currentImageNamed];
    _imgVLeft.image = [UIImage imageNamed:[NSString stringWithFormat:@"%lu.png", (unsigned long)((_currentImageIndex - 1 + _imageCount) % _imageCount)]];
    _imgVRight.image = [UIImage imageNamed:[NSString stringWithFormat:@"%lu.png", (unsigned long)((_currentImageIndex + 1) % _imageCount)]];
    
    _pageC.currentPage = currentImageIndex;
    _lblImageDesc.text = _mDicImageData[currentImageNamed];
}

- (void)setDefaultInfo {
    _currentImageIndex = 0;
    [self setInfoByCurrentImageIndex:_currentImageIndex];
}

- (void)reloadImage {
    CGPoint contentOffset = [_scrV contentOffset];
    if (contentOffset.x > kWidthOfScreen) { //向左滑动
        _currentImageIndex = (_currentImageIndex + 1) % _imageCount;
    } else if (contentOffset.x < kWidthOfScreen) { //向右滑动
        _currentImageIndex = (_currentImageIndex - 1 + _imageCount) % _imageCount;
    }
    
    [self setInfoByCurrentImageIndex:_currentImageIndex];
}

- (void)layoutUI {
    self.view.backgroundColor = [UIColor blackColor];
    
    [self loadImageData];
    [self addScrollView];
    [self addImageViewsToScrollView];
    [self addPageControl];
    [self addLabel];
    [self setDefaultInfo];
}

#pragma mark - UIScrollViewDelegate
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    [self reloadImage];
    
    _scrV.contentOffset = CGPointMake(kWidthOfScreen, 0.0);
    _pageC.currentPage = _currentImageIndex;
    
    NSString *currentImageNamed = [NSString stringWithFormat:@"%lu.png", (unsigned long)_currentImageIndex];
    _lblImageDesc.text = _mDicImageData[currentImageNamed];
}

@end

​ImageInfo.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>0.png</key>
    <string>WATCH，它，终于来了。</string>
    <key>1.png</key>
    <string>iPhone 6，无双，有此一双。</string>
    <key>2.png</key>
    <string>MacBook，轻于时代，先于时代。</string>
    <key>3.png</key>
    <string>iPad Air 2，轻轻地，改变一切。</string>
    <key>4.png</key>
    <string>iOS 9，它，将要到来。</string>
</dict>
</plist>