iOS 有关自动轮播图片

  //初始化当前视图
        _currentImageView = [[UIImageView alloc] init];
        [_currentImageView setImageWithURL:[NSURL URLWithString:[array_pic objectAtIndex:0]]];
        _currentImageView.frame = CGRectMake(myScroller.frame.size.width, 0, myScroller.frame.size.width,180);
//        _currentImageView.contentMode = UIViewContentModeScaleAspectFill;
        [myScroller addSubview:_currentImageView];

        _nextImageView = [[UIImageView alloc] init];
        [_nextImageView  setImageWithURL:[NSURL URLWithString:[array_pic objectAtIndex:1]]];
        _nextImageView.frame = CGRectMake(myScroller.frame.size.width * 2, 0,  myScroller.frame.size.width,180);
//        _nextImageView.contentMode = UIViewContentModeScaleAspectFill;
        [myScroller addSubview:_nextImageView];

        //初始化上一个视图
        _previousView = [[UIImageView alloc] init];
        [_previousView setImageWithURL:[NSURL URLWithString:[array_pic objectAtIndex:3]]];
        _previousView.frame = CGRectMake(0, 0,myScroller.frame.size.width,180);
//        _previousView.contentMode = UIViewContentModeScaleAspectFill;

        [myScroller addSubview:_previousView];

    }

    {
        SMPageControl *pageControl = [[SMPageControl alloc] init];
        [pageControl setFrame:CGRectMake(0, myScroller.frame.size.height+64 - 10.0f,myScroller.frame.size.width,10.0f)];
        [pageControl setNumberOfPages:4];
        [pageControl setBackgroundColor:[UIColor clearColor]];
        [pageControl setCurrentPage:0];
        [pageControl setCurrentPageIndicatorTintColor:[UIColor lightGrayColor]];
        [pageControl setPageIndicatorTintColor:[UIColor grayColor]];
        myPageControl=pageControl;
        [self.view addSubview:myPageControl];
    }

if (![myTimer isValid]) {
        myTimer=[NSTimer scheduledTimerWithTimeInterval:5 target:self selector:@selector(updateAuto) userInfo:nil repeats:YES];
    }

#pragma mark 时钟动画调用方法
- (void)updateAuto
{
    if (_isDraging) {
        return;
    }

    CGPoint offset = myScroller.contentOffset;

    offset.x += self.view.frame.size.width;
    if (offset.x > self.view.frame.size.width*2) {
        offset.x = self.view.frame.size.width;
    }

    [myScroller setContentOffset:offset animated:YES];
}

#pragma mark - 代理方法
 #pragma mark 准备开始拖动
 - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
 {
         _isDraging = YES;
     }

 #pragma mark 视图停止滚动
 - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
 {
         _isDraging = NO;
}

#pragma mark 已经拖动
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{

    static int i = 0;//当前展示的是第几张图片

    float offset = scrollView.contentOffset.x;
    if (_nextImageView.image == nil || _previousView.image == nil) {

        //加载下一个视图
        [_nextImageView setImageWithURL:[NSURL URLWithString:[array_pic objectAtIndex:i == kCount ? 0: i+1]]];

        //加载上一个视图
        [_previousView setImageWithURL:[NSURL URLWithString:[array_pic objectAtIndex:i == 0 ? kCount : i - 1]]];
    }

    if (offset == 0) {
        _currentImageView.image = _previousView.image;
        scrollView.contentOffset = CGPointMake(scrollView.bounds.size.width, 0);
        _previousView.image = nil;

        if (i == 0) {
            i = kCount;
        }else{
            i -= 1;
        }

    }

    if (offset == scrollView.bounds.size.width * 2) {
        _currentImageView.image = _nextImageView.image;
        scrollView.contentOffset = CGPointMake(scrollView.bounds.size.width, 0);
        _nextImageView.image = nil;

        if (i == kCount) {
            i = 0;  //如果当前图片索引在最后一个，则重置为0,否则+1
        }else{
            i += 1;
        }
    }
     [myPageControl setCurrentPage:i];
}