不间断旋转的动画

CABasicAnimation* rotationAnimation;
    rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    rotationAnimation.toValue = [NSNumber numberWithFloat: M_PI * 2.0 /* full rotation*/ * rotations * duration ];
    rotationAnimation.duration = duration;
    rotationAnimation.cumulative = YES; /*可以不写这句*/
    rotationAnimation.repeatCount = repeat;

    [view.layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];


我的实际代码
let rotation = CABasicAnimation(keyPath: "transform.rotation.z")
rotation.toValue = NSNumber(float: Float(2 * M_PI))
rotation.duration = 0.2
rotation.repeatCount = Float(CGFloat.max)
cancelButton.layer.addAnimation(rotation, forKey: nil)