iOS利用UIScrollView实现无限滚动效果

#import "ViewController.h"

//屏幕宽度
#define SCREEN_WIDTH [UIScreen mainScreen].bounds.size.width
//图片高度
#define IMG_HEIGHT 180
//要显示的图片总数
#define MAX_SIZE 7

#import "ViewController.h"

@interface ViewController () <UIScrollViewDelegate>

//滚动视图
@property (strong, nonatomic) UIScrollView *loopScrollView;
//指示器
@property (strong, nonatomic) UIPageControl *pageIndicator;
//要展示的图片数组
@property(strong, nonatomic) NSMutableArray *imgArray;

@end

@implementation ViewController

//懒加载数组
-(NSMutableArray *)imgArray
{
  if(_imgArray == nil)
  {
    _imgArray = [[NSMutableArray alloc]initWithCapacity:MAX_SIZE];
    //在要展示的5张图片的前后各加一张图片，第一张前面加第五张，第五张后面加第一张
    [_imgArray addObject:[UIImage imageNamed:@"img_05.jpg"]];
    for (int i = 1; i< MAX_SIZE - 1; i++) {
      NSString *imgName = [[NSString alloc]initWithFormat:@"img_0%d.jpg", i];
      [_imgArray addObject:[UIImage imageNamed:imgName]];
    }
    [_imgArray addObject:[UIImage imageNamed:@"img_01.jpg"]];

  }
  return _imgArray;
}


- (void)viewDidLoad {
  [super viewDidLoad];

  [self setupScrollView];
  [self setupPageControl];

}

/**
 * 创建UIScrollView并设置其属性
 */
-(void)setupScrollView
{
  UIScrollView *sc = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 64, SCREEN_WIDTH, IMG_HEIGHT)];

  //创建UIImageView并添加到UIScrollView中
  for (int i = 0; i< MAX_SIZE; i++) {
    UIImageView *img = [[UIImageView alloc]initWithImage:[self.imgArray objectAtIndex:i]];
    img.frame = CGRectMake(SCREEN_WIDTH * i, 0, SCREEN_WIDTH, IMG_HEIGHT);
    [sc addSubview:img];
  }

  //设置UIScrollView的属性
  sc.contentSize = CGSizeMake(SCREEN_WIDTH * self.imgArray.count, IMG_HEIGHT);
  sc.showsHorizontalScrollIndicator = NO;
  sc.pagingEnabled = YES;
  //刚开始应该滚动到第二张显示，因为第一张其实是最后一张图片
  [sc setContentOffset:CGPointMake(SCREEN_WIDTH, 0) animated:NO];


  //设置代理并添加到当前view中
  sc.delegate = self;
  [self.view addSubview:sc];

  self.loopScrollView = sc;
}


/**
 * 创建UIPageControl并设置其属性
 */
-(void)setupPageControl
{
  //注意frame，这样设置可以居中显示
  UIPageControl *pc = [[UIPageControl alloc]initWithFrame:CGRectMake(self.view.center.x - 50, CGRectGetMaxY(self.loopScrollView.frame) - 25 , 100, 25)];
  //设置UIPageControl的属性并添加到当前view中
  pc.numberOfPages = MAX_SIZE - 2;
  pc.currentPage = 0;
  pc.pageIndicatorTintColor = [UIColor redColor];
  [self.view addSubview:pc];

  self.pageIndicator = pc;

}

//UIScrollView的代理方法，在该方法中改变UIPageControl并且处理边缘滚动
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
  //获取当前UIScrollView的位置
  CGPoint offset = [scrollView contentOffset];
  //算出滚动到第几页
  int currentPage = offset.x/SCREEN_WIDTH;
  //设置UIPageControl
  self.pageIndicator.currentPage = currentPage - 1;
  //对最后一张和第一张要进行特殊处理
  //1、如果是第一张
  if (currentPage == 0) {
    //下面两个方法任选其一都可以达到效果，但是注意动画一定要设置为NO，不然会有视觉会有辣眼睛的感觉
    //方法1
    [self.loopScrollView setContentOffset:CGPointMake(SCREEN_WIDTH * (MAX_SIZE-2), 0) animated:NO];
    //方法2，该方法要求设置contentSize时，任一方向就算不滚动也不能为0，否则无效
    //[self.loopScrollView scrollRectToVisible:CGRectMake(SCREEN_WIDTH * (MAX_SIZE-2), 0, SCREEN_WIDTH, IMG_HEIGHT) animated:NO];
    self.pageIndicator.currentPage = MAX_SIZE - 2;
  }

  //2、如果是最后一张
  else if(currentPage == MAX_SIZE - 1) {
    [self.loopScrollView setContentOffset:CGPointMake(SCREEN_WIDTH, 0) animated:NO];
    //[self.loopScrollView scrollRectToVisible:CGRectMake(SCREEN_WIDTH, 0, SCREEN_WIDTH, IMG_HEIGHT) animated:NO];
    self.pageIndicator.currentPage = 0;
  }
}

@end