最近项目中用到了一些动画效果，研究的过程中发现挺有意思，那就分享一下喽!
首先看一下素材：

下面是实现后的效果：

代码如下：

#import <UIKit/UIKit.h>

@interface LSZClockView : UIView

- (instancetype)initWithFrame:(CGRect)frame imageName:(NSString *)imageName;

@end

#import "LSZClockView.h"

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

@interface LSZClockView()

/** 背景图片 */
@property (nonatomic, copy) NSString *imageName;
/** 时针 */
@property (nonatomic, strong) CALayer *hourLayer;
/** 分针 */
@property (nonatomic, strong) CALayer *minuteLayer;
/** 秒针 */
@property (nonatomic, strong) CALayer *secondLayer;
/** Timer */
@property (nonatomic, strong) NSTimer *timer;
/** 日期组 */
@property (nonatomic, strong) NSDateComponents *dateComponents;

@end

@implementation LSZClockView

#pragma mark - Life Circle

- (void)dealloc {
    if (_timer) {
        [_timer invalidate];
        _timer = nil;
    }
}

- (instancetype)initWithFrame:(CGRect)frame imageName:(NSString *)imageName {
    if (self = [super initWithFrame:frame]) {
        self.imageName = imageName;
        [self buildView];
    }
    return self;
}

- (void)buildView {
    // 设置时钟背景图片
    @autoreleasepool {
        self.layer.contents = (__bridge id)[UIImage imageNamed:self.imageName].CGImage;
    }
    // 设置timer
    
}

- (void)layoutSubviews {
    [super layoutSubviews];
    // 延迟添加各layer
    [self.layer addSublayer:self.hourLayer];
    [self.layer addSublayer:self.minuteLayer];
    [self.layer addSublayer:self.secondLayer];
    self.secondLayer.cornerRadius = 0;
    // 开启timer 需关闭动画
//    if (self.timer.valid) {}
    
}

#pragma mark - Tool Method

- (CALayer *)layerWithBackgroundColor:(UIColor *)color size:(CGSize)size {
    CALayer *layer = [CALayer layer];
    // 设置背景色
    layer.backgroundColor = color.CGColor;
    // 设置锚点
    layer.anchorPoint = CGPointMake(0.5, 1);
    // 设置为 self 中心
    layer.position = CGPointMake(self.frame.size.width * 0.5, self.frame.size.height * 0.5);
    // 设置size
    layer.bounds = CGRectMake(0, 0, size.width, size.height);
    // 设置圆角
    layer.cornerRadius = 2;
    return layer;
}

- (CABasicAnimation *)animationWithAngle:(CGFloat)angle duration:(CFTimeInterval)duration{
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    animation.repeatCount = HUGE_VALF;
    animation.duration = duration;
    animation.removedOnCompletion = NO;
    animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    animation.fromValue = @(angle * M_PI / 180);
    animation.byValue = @(2 * M_PI);
    return animation;
}

#pragma mark - Event

- (void)timerInterval {
    // 获取当前时分秒数据
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *components = [calendar components:NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond fromDate:[NSDate date]];
    NSInteger hour = components.hour;
    NSInteger minute = components.minute;
    NSInteger second = components.second;
    // 时针角度
    CGFloat hourUnitAngle = 1.0 / 12.0 * 360;
    CGFloat hourAngle = hour * hourUnitAngle + minute * 1.0  / 60 * hourUnitAngle;
    self.hourLayer.transform = CATransform3DMakeRotation(kAngleToRadion(hourAngle), 0, 0, 1);
    // 分针角度
    CGFloat minuteAngle = minute * 1.0 / 60.0 * 360;
    self.minuteLayer.transform = CATransform3DMakeRotation(kAngleToRadion(minuteAngle), 0, 0, 1);
    // 秒针角度
    CGFloat secondAngle = second * 1.0 / 60.0 * 360;
    self.secondLayer.transform = CATransform3DMakeRotation(kAngleToRadion(secondAngle), 0, 0, 1);
}

#pragma mark - Property

- (CALayer *)hourLayer {
    if (!_hourLayer) {
        _hourLayer = [self layerWithBackgroundColor:[UIColor blackColor] size:CGSizeMake(3, self.frame.size.height * 0.5 - 40)];
        CGFloat hourUnitAngle = 1.0 / 12.0 * 360;
        CGFloat hourAngle = self.dateComponents.hour * hourUnitAngle + self.dateComponents.minute * 1.0  / 60 * hourUnitAngle;
        [_hourLayer addAnimation:[self animationWithAngle:hourAngle duration:60 * 60 * 12]  forKey:@"HourAnimationKey"];
    }
    return _hourLayer;
}

- (CALayer *)minuteLayer {
    if (!_minuteLayer) {
        _minuteLayer = [self layerWithBackgroundColor:[UIColor blackColor] size:CGSizeMake(3, self.frame.size.height * 0.5 - 25)];
        CGFloat minuteAngle = self.dateComponents.minute * 1.0 / 60.0 * 360;
        [_minuteLayer addAnimation:[self animationWithAngle:minuteAngle duration:60 * 60]  forKey:@"MinuteAnimationKey"];
    }
    return _minuteLayer;
}

- (CALayer *)secondLayer {
    if (!_secondLayer) {
        _secondLayer = [self layerWithBackgroundColor:[UIColor blackColor] size:CGSizeMake(1, self.frame.size.height * 0.5 - 20)];
        CGFloat secondAngle = self.dateComponents.second * 1.0 / 60.0 * 360;
        [_secondLayer addAnimation:[self animationWithAngle:secondAngle duration:60]  forKey:@"SecondAnimationKey"];
    }
    return _secondLayer;
}

- (NSTimer *)timer {
    if (!_timer) {
        _timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(timerInterval) userInfo:nil repeats:YES];
        [[NSRunLoop currentRunLoop] addTimer:_timer forMode:NSRunLoopCommonModes];
        [self timerInterval];
    }
    return _timer;
}

- (NSDateComponents *)dateComponents {
    if (!_dateComponents) {
        NSCalendar *calendar = [NSCalendar currentCalendar];
        _dateComponents = [calendar components:NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond fromDate:[NSDate date]];
    }
    return _dateComponents;
}

这么调用的：

LSZClockView *clockView = [[LSZClockView alloc] initWithFrame:CGRectMake([UIScreen mainScreen].bounds.size.width * 0.5 - 100, 50, 200, 200) imageName:@"clock"];
    [self.view addSubview:clockView];

说明一下：
1、代码中包含了用Timer 和 CABasicAnimation两种方式的实现；
2、运行后会发现CALayer会有虚化现象，目前尝试过设置shouldRasterize，但这种方式在有动画效果或calayer不断形变的时候会有缓存问题，果断放弃。目前能够想到的是自己去画线，有兴趣的同学可以试试。