scrollView实现轮播

scrollView实现轮播

• 假设现在我们有5张图片需要实现轮播效果，我实现轮播的方法是在第一张图片前插入最后一张，在最后一张后添加第一张，当滚动到添加后的最后一张时，contentoffset.x = screen_w，也就是到了插入前第一张；同理针对插入前的一张。
• 代码：

1./**
2. * @brief 创建轮播,在tableView创建之后和数据加载后
3. */
4.-(void)createCarousel{
5.    UIView *carouselBack = [[UIView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_W, CAROUSEL_HEIGHT)];
6.
7.    NSInteger numberOfAd = self.topStories.count - 2;
8.
9.    _carousel = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, SCREEN_W, CAROUSEL_HEIGHT)];
10.    _carousel.delegate = self;
11.    _carousel.showsHorizontalScrollIndicator = NO;
12.    _carousel.showsVerticalScrollIndicator = NO;
13.    _carousel.bounces = NO;
14.    _carousel.pagingEnabled = YES;
15.    _carousel.contentSize = CGSizeMake(self.topStories.count * SCREEN_W, CAROUSEL_HEIGHT);
16.
17.    for (int i = 0; i < self.topStories.count; i++) {
18.        JKTopStory *topStory = self.topStories[i];
19.        UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(SCREEN_W * i, 0, SCREEN_W, CAROUSEL_HEIGHT)];
20.        NSURL *url = [NSURL URLWithString:topStory.image];
21.        [imageView setImageWithURL:url];
22.        [_carousel addSubview:imageView];
23.    }
24.    _carousel.contentOffset = CGPointMake(SCREEN_W, 0);
25.
26.
27.    [carouselBack addSubview:_carousel];
28.
29.    _pageControl = [[UIPageControl alloc] initWithFrame:CGRectMake(0, 0, SCREEN_W * 0.2, 10)];
30.    _pageControl.numberOfPages = numberOfAd;
31.    _pageControl.pageIndicatorTintColor = [UIColor lightGrayColor];
32.    _pageControl.currentPageIndicatorTintColor = [UIColor whiteColor];
33.    _pageControl.center = CGPointMake(SCREEN_W * 0.5, CAROUSEL_HEIGHT - 20);
34.    _pageControl.tintColor = [UIColor colorWithRed:0.8 green:0.8 blue:0.8 alpha:1];
35.    [carouselBack addSubview:_pageControl];
36.
37.    self.storyTableView.tableHeaderView = carouselBack;
38.
39.    _timer = [NSTimer scheduledTimerWithTimeInterval:5.0f target:self selector:@selector(doScroll) userInfo:nil repeats:YES];
40.}
41.#pragma mark - scrollView的代理方法
42.-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
43.    if (scrollView == _carousel) {
44.        if (scrollView.contentOffset.x == SCREEN_W * (self.topStories.count -1)) {
45.            scrollView.contentOffset = CGPointMake(SCREEN_W, 0);
46.        }else if (scrollView.contentOffset.x == 0){
47.            scrollView.contentOffset = (CGPoint){SCREEN_W * (self.topStories.count - 2),0};
48.        }
49.    }
50.}
51.-(void)scrollViewDidScroll:(UIScrollView *)scrollView{
52.    if (scrollView == _carousel) {
53.        CGPoint offset = scrollView.contentOffset;
54.        _pageControl.currentPage = offset.x / SCREEN_W - 1;
55.    }
56.}
57.// 关于drag方法，可以避免手动拖动后与timer的执行时间相撞，从而连续滚动两张图片
58.-(void)scrollViewWillBeginDragging:(UIScrollView *)scrollView{
59.    [_timer invalidate];
60.}
61.-(void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
62.    _timer = nil;
63.    _timer = [NSTimer scheduledTimerWithTimeInterval:5.0f target:self selector:@selector(doScroll) userInfo:nil repeats:YES];
64.}
65.
66.#pragma mark - 定时器回调
67.-(void)doScroll{
68.    __block CGPoint offset = _carousel.contentOffset;
69.    offset.x += SCREEN_W;
70.    [UIView animateWithDuration:1.0f animations:^{
71.        _carousel.contentOffset = offset;
72.    } completion:^(BOOL finished) {
73.        if (offset.x == SCREEN_W * (self.topStories.count - 1)) {
74.            offset = (CGPoint){SCREEN_W,offset.y};
75.            _carousel.contentOffset = offset;
76.        }
77.        _pageControl.currentPage = offset.x / SCREEN_W - 1;
78.    }];
79.}

• 演示：