CALayer所有的旋转和缩放都是围绕锚点进行的。UIView的center是相对于父控件而言的

#import "ViewController.h"

#define angleToRadio(angle) ((angle) * M_PI / 180.0)

//每一秒旋转6度
#define perSecA 6

//每一分旋转6度
#define perMinA 6

//每一小时旋转 30 度
#define perHourA 30

//每一分时针旋转多少度 0.5
#define  perMinHourA 0.5

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIImageView *colockView;
@property (weak, nonatomic) CALayer *secL;
@property (weak, nonatomic) CALayer *minL;
@property (weak, nonatomic) CALayer *hourL;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //所有的旋转,缩放都是绕着锚点进行的.
    //添加时针
    [self addHourL];
    
    //添加分针
    [self addMinL];
    
    //添加秒针
    [self addSecL];
   
    //添加定时器
    [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timeChange) userInfo:nil repeats:YES];
    
    [self timeChange];
}

- (void)timeChange {
    //让秒针开始旋转
    //获取当前的秒数
    //获取当前的日历
    NSCalendar *cal = [NSCalendar currentCalendar];
    //从什么时间获取日历当中的哪些组件(年,月,日,时,分,秒)
    NSDateComponents *cpt = [cal components:NSCalendarUnitSecond | NSCalendarUnitMinute | NSCalendarUnitHour fromDate:[NSDate date]];
    //当前时间的秒数
    NSInteger curSec =  cpt.second;
    NSInteger curMin = cpt.minute;
    NSInteger curHour = cpt.hour;
    NSLog(@"%ld-%ld-%ld",curHour,curMin,curSec);
    
    //求角度 = 当前的秒数 * 每一秒旋转多少度
    CGFloat secA = curSec * perSecA;
    self.secL.transform = CATransform3DMakeRotation(angleToRadio(secA), 0, 0, 1);
    
    //旋转分针
    //求角度 = 当前多少分 * 每一分旋转多少度
    CGFloat minA = curMin * perMinA;
    self.minL.transform =  CATransform3DMakeRotation(angleToRadio(minA), 0, 0, 1);
    
    //旋转时针
    //求角度 = 当前多少小时 * 每一小时旋转多少度
    CGFloat hourA = curHour * perHourA + curMin * perMinHourA;
    self.hourL.transform =  CATransform3DMakeRotation(angleToRadio(hourA), 0, 0, 1);
}

//所有的旋转,缩放都是绕着锚点进行的.
- (void)addSecL {
    CALayer *secL = [CALayer layer];
    secL.backgroundColor = [UIColor redColor].CGColor;
    secL.bounds = CGRectMake(0, 0, 1, 80);
    
    secL.anchorPoint = CGPointMake(0.5, 1);
    secL.position = CGPointMake(self.colockView.bounds.size.width * 0.5, self.colockView.bounds.size.height * 0.5);
    
    [self.colockView.layer addSublayer:secL];
    self.secL = secL;
}

- (void)addMinL {
    CALayer *minL = [CALayer layer];
    minL.backgroundColor = [UIColor blackColor].CGColor;
    minL.bounds = CGRectMake(0, 0, 2, 70);
    minL.anchorPoint = CGPointMake(0.5, 1);
    minL.position = CGPointMake(self.colockView.bounds.size.width * 0.5, self.colockView.bounds.size.height * 0.5);
    
    [self.colockView.layer addSublayer:minL];
    self.minL = minL;
}

- (void)addHourL {
    CALayer *hourL = [CALayer layer];
    hourL.backgroundColor = [UIColor blackColor].CGColor;
    hourL.bounds = CGRectMake(0, 0, 3, 60);
    hourL.anchorPoint = CGPointMake(0.5, 1);
    hourL.position = CGPointMake(self.colockView.bounds.size.width * 0.5, self.colockView.bounds.size.height * 0.5);
    
    [self.colockView.layer addSublayer:hourL];
    self.hourL = hourL;
}

@end

时钟效果代码如上