iOS UIScrollView循环拖动的思路和实现方法

首先声明，这个代码和思路是借鉴大神的，下面文章的链接处有文章的出处，尊重原创，自己钻研了下，想把实现的思路更详细的记录一下。

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</uiscrollviewdelegate></uikit>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) { //向右滑动_currentImageIndex = (_currentImageIndex + 1) % _imageCount;} else if (contentOffset.x < kWidthOfScreen) { //向左滑动_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];}@endImageInfo.plist<!--?xml version="1.0" encoding="UTF-8"?--><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 version="1.0">

实现效果接下来是自己的理解和详细思路1.首先创建试图，UIScrollView,UIImageView,UILabel,UIPageControl.创建的时候，设置UIScrollView的contentSize为屏幕的三倍大小，所以UIScrollView有三张屏幕的大小，最初显示的时候是现实最中间的那一屏。创建左_imgVLeft、中_imgVCenter、右_imgVRight三张UIImageView，分别放在UIScrollView对应的三张屏。当前屏幕显示的是UIScrollView的中间那一部分，显示UIImageView的中间_imgVCenter的那张图片。2.设置默认设置的时候，setDefaultInfo方法，其实是通过_currentImageIndex来设置图片的展示。3.拖拽UIScrollView的时候，

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {

4.最后总结，就想当与一张大纸（UIScrollView）上有三个框，左，中，右（相当于与屏幕的大小），最开始显示中间的那个框，通过拖拽，先转换框中的图片，根据拖拽的方向，换成原先图片左边或右边的那张，然后通过设置偏移量又回到最开始的状态，只是框中的图片换了。