iOS中的定时器实现图片的轮播

#import "YYViewController.h"

@interface YYViewController () <UIScrollViewDelegate>
@property (weak, nonatomic) IBOutlet UIScrollView *scrollview;
/**
 *  页码
 */
@property (weak, nonatomic) IBOutlet UIPageControl *pageControl;

@property (nonatomic, strong) NSTimer *timer;
@end

@implementation YYViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

//    图片的宽
    CGFloat imageW = self.scrollview.frame.size.width;
//    CGFloat imageW = 300;
//    图片高
    CGFloat imageH = self.scrollview.frame.size.height;
//    图片的Y
    CGFloat imageY = 0;
//    图片中数
    NSInteger totalCount = 5;
//   1.添加5张图片
    for (int i = 0; i < totalCount; i++) {
        UIImageView *imageView = [[UIImageView alloc] init];
//        图片X
        CGFloat imageX = i * imageW;
//        设置frame
        imageView.frame = CGRectMake(imageX, imageY, imageW, imageH);
//        设置图片
        NSString *name = [NSString stringWithFormat:@"img_0%d", i + 1];
        imageView.image = [UIImage imageNamed:name];
//        隐藏指示条
        self.scrollview.showsHorizontalScrollIndicator = NO;

        [self.scrollview addSubview:imageView];
    }

//    2.设置scrollview的滚动范围
    CGFloat contentW = totalCount *imageW;
    //不允许在垂直方向上进行滚动
    self.scrollview.contentSize = CGSizeMake(contentW, 0);

//    3.设置分页
    self.scrollview.pagingEnabled = YES;

//    4.监听scrollview的滚动
    self.scrollview.delegate = self;

    [self addTimer];
}

- (void)nextImage
{
    int page = (int)self.pageControl.currentPage;
    if (page == 4) {
        page = 0;
    }else
    {
        page++;
    }

//  滚动scrollview
    CGFloat x = page * self.scrollview.frame.size.width;
    self.scrollview.contentOffset = CGPointMake(x, 0);
}

// scrollview滚动的时候调用
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    NSLog(@"滚动中");
//    计算页码
//    页码 = (contentoffset.x + scrollView一半宽度)/scrollView宽度
    CGFloat scrollviewW =  scrollView.frame.size.width;
    CGFloat x = scrollView.contentOffset.x;
    int page = (x + scrollviewW / 2) /  scrollviewW;
    self.pageControl.currentPage = page;
}

// 开始拖拽的时候调用
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
//    关闭定时器(注意点; 定时器一旦被关闭,无法再开启)
//    [self.timer invalidate];
    [self removeTimer];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
//    开启定时器
    [self addTimer];
}

/**
 *  开启定时器
 */
- (void)addTimer{

    self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(nextImage) userInfo:nil repeats:YES];
106 }
/**
 *  关闭定时器
 */
- (void)removeTimer
{
    [self.timer invalidate];
}
@end

提示：以下两个属性已经和storyboard中的控件进行了连线。

@property (weak, nonatomic) IBOutletUIScrollView *scrollview;

@property (weak, nonatomic) IBOutletUIPageControl *pageControl;

补充：定时器NSTimer

   定时器 适合用来隔一段时间做一些间隔比较长的操作

 NSTimeInterval:多长多件操作一次

 target :操作谁

 selector : 要操作的方法

 userInfo: 传递参数

 repeats: 是否重复

  self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(nextImage) userInfo:nil repeats:YES];