关于UIScrollView无限循环滑动

在使用某宝或某东购物的时候,我们会在其首页看到一个可以滑动的版块,这个版块的实现就是一个UIScrollView.在我们使用UIScrollView的时候会发现,滑动到最后的时候,UIScrollView不能像上面说的版块那样又回到最初的地方.基于此,做了一个小Demo来实现UIScrollView的无限循环滑动.

小小思路:UIScrollView具有分页属性,要实现UIScrollView的无限循环滑动,我们不能生硬暴力的给一个数组按规律的,无限的添加图片,这样手机内存还不爆炸 0.0 , 如何用最少的页面实现无限循环呢? 三个,其实只需要三个页面就可以实现UIScrollView的无限循环滑动.左丶中丶右 三个页面.刚进入程序时,左边放最后一张图片,中间第一张图片,右边放第二张.向左滑动一张图片,左边变成了第一张图片,中间是第二张,右边则变成了第三张图片.依此便可实现UIScrollView的无限循环滑动了.

Demo 如下 :
.h文件
声明一个数组来接收外部传入的图片

@interface MyScrollView: UIView <UIScrollViewDelegate>

@property(nonatomic, strong)NSArray *dataArr;

@end

.m文件
实现无线循环滑动

#define kPageCtrlHeight 37  //UIPageControl的高度

@interface MyScrollView ()
{

      UIImageView *leftView;
      UIImageView *centerView;
      UIImageView *rightView;
    
      UIScrollView *scrollView;
      UIPageControl *pageCtrl;    // 页面控制器 ...
    
      NSInteger currentPageNumber;
}

@end

@implementation MyScrollView

/*----------------始终只有左,中,右3个imgView,将数据源加入到这3个imgView中显示--------------------------*/

- (instancetype)init
{

      return [self initWithFrame:[UIScreen mainScreen].bounds];
}

- (instancetype)initWithFrame:(CGRect)frame
{

      self = [super initWithFrame:frame];
      if (self) {
          [self createUI:frame];
      }
      return self;
}

-(void)createUI:(CGRect)frame
{

      scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, frame.size.width, frame.size.height - kPageCtrlHeight)];
      scrollView.delegate = self;
      scrollView.pagingEnabled = YES;
      scrollView.showsHorizontalScrollIndicator = NO;
      scrollView.showsVerticalScrollIndicator = NO;
      
      pageCtrl = [[UIPageControl alloc] initWithFrame:CGRectMake(0, frame.size.height - kPageCtrlHeight, frame.size.width, kPageCtrlHeight)];
      pageCtrl.backgroundColor = [UIColor lightGrayColor];
    
      [self addSubview:scrollView];
      [self addSubview:pageCtrl];
    
    
      leftView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
      centerView = [[UIImageView alloc] initWithFrame:CGRectMake(scrollView.frame.size.width, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
      rightView = [[UIImageView alloc] initWithFrame:CGRectMake(scrollView.frame.size.width*2, 0, scrollView.frame.size.width, scrollView.frame.size.height)];
    
      [scrollView addSubview:leftView];
      [scrollView addSubview:centerView];
      [scrollView addSubview:rightView];
}


-(void)setDataArr:(NSArray *)dataArr
{

      if (![dataArr isKindOfClass:[NSArray class]] || dataArr.count == 0) {
          return;
      }
    
      _dataArr = dataArr;
    
      [self setInitProperty];
}

-(void)setInitProperty
{

      pageCtrl.numberOfPages = _dataArr.count;  //总页码
      //内容
      scrollView.contentSize = CGSizeMake(_dataArr.count * scrollView.frame.size.width, scrollView.frame.size.height);
      [scrollView setContentOffset:CGPointMake(scrollView.frame.size.width, 0)];//偏移位置,第一页
    
      currentPageNumber = 0;
      [self loadPageContent];
}

-(void)loadPageContent
{

      centerView.image = [UIImage imageNamed:_dataArr[currentPageNumber]];
    
      NSInteger leftImgIndex = (currentPageNumber - 1 + _dataArr.count) % _dataArr.count;
      leftView.image = [UIImage imageNamed:_dataArr[leftImgIndex]];
    
      NSInteger rightImgIndex = (currentPageNumber + 1) % _dataArr.count;
      rightView.image = [UIImage imageNamed:_dataArr[rightImgIndex]];
    
      pageCtrl.currentPage = currentPageNumber;
}

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

      if (scrollView.contentOffset.x > scrollView.bounds.size.width) {    //向左滑动
          currentPageNumber = (currentPageNumber + 1) % _dataArr.count;
      }else if (scrollView.contentOffset.x < scrollView.bounds.size.width){   //向右滑动
          currentPageNumber = (currentPageNumber - 1 + _dataArr.count) % _dataArr.count;
      }
    
      [self loadPageContent];
    
      scrollView.contentOffset = CGPointMake(scrollView.bounds.size.width, 0);
}

@end

ViewController.m 文件:
对myScrollView初始化并
调用myScrollView中dataArr setter方法即可。

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