简单轮播图

#import "ViewController.h"

#define screen_W [UIScreen mainScreen].bounds.size.width

@interface ViewController ()<UIScrollViewDelegate>

@property (strong, nonatomic) UIScrollView *scrollView;
@property (strong, nonatomic) UIPageControl *pageControl;
@property (nonatomic ,weak) NSTimer *timer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self.navigationController setNavigationBarHidden:YES animated:NO];
    [self.view addSubview:self.scrollView];
    [self.view addSubview:self.pageControl];
    [self startTimer];
}

- (UIScrollView *)scrollView {
    if (!_scrollView) {
        _scrollView = [[UIScrollView alloc] init];
        _scrollView.frame = CGRectMake(0, 100, screen_W, 400);
        _scrollView.delegate = self;
        _scrollView.pagingEnabled = YES;
        _scrollView.contentSize = CGSizeMake(screen_W * 4, 400);
        _scrollView.bounces = NO;
        _scrollView.showsHorizontalScrollIndicator = NO;
        _scrollView.showsHorizontalScrollIndicator = NO;
        for (NSInteger i = 0; i < 4; i++) {
            UIImageView *imageView = [[UIImageView alloc] init];
            imageView.frame = CGRectMake(i * screen_W, 0, screen_W, 400);
            imageView.image = [UIImage imageNamed:[NSString stringWithFormat:@"%ld",i]];
            [_scrollView addSubview:imageView];
        }
    }
    return _scrollView;
}

- (UIPageControl *)pageControl {
    if (!_pageControl) {
        _pageControl = [[UIPageControl alloc] init];
        _pageControl.frame = CGRectMake(0, 510, screen_W, 20);
        _pageControl.numberOfPages = 4;
        _pageControl.hidesForSinglePage = YES;
        [_pageControl setValue:[UIImage imageNamed:@"current"] forKeyPath:@"currentPageImage"];
        [_pageControl setValue:[UIImage imageNamed:@"other"] forKeyPath:@"pageImage"];
    }
    return _pageControl;
}

- (void)startTimer {
    self.timer = [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(nextPage) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

- (void)stopTimer {
    [self.timer invalidate];
}

- (void)nextPage {
    NSInteger page = self.pageControl.currentPage + 1;
    if (page == 4) {
        page = 0;
    }
    [self.scrollView setContentOffset:CGPointMake(page * self.scrollView.frame.size.width, 0) animated:YES];
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    int page = (int)(self.scrollView.contentOffset.x / self.scrollView.frame.size.width + 0.5);
    self.pageControl.currentPage = page;
}

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
    [self stopTimer];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    [self startTimer];
}

@end