缓动函数与关键帧动画

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    // 显示参考用的view
    UIView *showView = [[UIView alloc] initWithFrame:CGRectMake(0, 20, 300, 300)];
    showView.layer.borderWidth = 1.f;
    showView.layer.cornerRadius = 150.f;
    showView.layer.borderColor = [UIColor redColor].CGColor;
    showView.center = self.view.center;
    [self.view addSubview:showView];
    
    // 新建layer
    CALayer *layer = [CALayer layer];
    layer.backgroundColor = [UIColor blackColor].CGColor;
    
    // 重置锚点
    layer.anchorPoint = CGPointMake(0.f, 0.f);
    
    // 设置layer的frame值(在showView正中间摆放)
    layer.frame = CGRectMake(showView.middleX, showView.middleY, 1, 150);
    
    // 添加进showView中
    [showView.layer addSublayer:layer];
    
    // 定时器
    _timer = [[GCDTimer alloc] initInQueue:[GCDQueue mainQueue]];
    [_timer event:^{
        static int i = 1;
        
        // 计算好起始值,结束值
        CGFloat oldValue = DEGREES_TO_RADIANS((360/60.f) * i++);
        CGFloat newValue = DEGREES_TO_RADIANS((360/60.f) * i);
        
        // 关键帧动画
        CAKeyframeAnimation *animation =             [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];
        
        // 设置值
        [animation setValues:[YXEasing calculateFrameFromValue:oldValue
                                                       toValue:newValue
                                                          func:ElasticEaseOut
                                                    frameCount:500]];
        // 设置持续时间
        animation.duration  = 0.5f;


        // 每秒增加的角度(设定结果值,在提交动画之前执行)
        layer.transform =         CATransform3DMakeRotation(newValue, 0.0, 0.0, 1.0);
        
        // 提交动画
        [layer addAnimation:animation forKey:nil];
    } timeInterval:NSEC_PER_SEC];
    [_timer start];
}