ios - 使用 animateKeyframesWithDuration 在屏幕上创建一个连续旋转的正方形

Question

我尝试使用下面的代码在屏幕上创建一个连续旋转的正方形。但我不知道为什么转速在变化。我怎样才能改变代码使转速不变？我尝试了不同的 UIViewKeyframeAnimationOptions，但似乎都不起作用。

override func viewDidLoad() {
    super.viewDidLoad()

    let square = UIView()
    square.frame = CGRect(x: 55, y: 300, width: 40, height: 40)
    square.backgroundColor = UIColor.redColor()
    self.view.addSubview(square)

    let duration = 1.0
    let delay = 0.0
    let options = UIViewKeyframeAnimationOptions.Repeat
        UIView.animateKeyframesWithDuration(duration, delay: delay, options: options, animations: {
        let fullRotation = CGFloat(M_PI * 2)

        UIView.addKeyframeWithRelativeStartTime(0, relativeDuration: 1/3, animations: {
            square.transform = CGAffineTransformMakeRotation(1/3 * fullRotation)
        })                        
        UIView.addKeyframeWithRelativeStartTime(1/3, relativeDuration: 1/3, animations: {
            square.transform = CGAffineTransformMakeRotation(2/3 * fullRotation)
        })                        
        UIView.addKeyframeWithRelativeStartTime(2/3, relativeDuration: 1/3, animations: {
            square.transform = CGAffineTransformMakeRotation(3/3 * fullRotation)
        })
        }, completion: {finished in
        })
    }         

Answer 1

我以前也遇到过同样的问题，我是这样解决的:

swift 2

let raw = UIViewKeyframeAnimationOptions.Repeat.rawValue | UIViewAnimationOptions.CurveLinear.rawValue
let options = UIViewKeyframeAnimationOptions(rawValue: raw)

swift 3、4、5

let raw = UIView.KeyframeAnimationOptions.repeat.rawValue | UIView.AnimationOptions.curveLinear.rawValue
let options = UIView.KeyframeAnimationOptions(rawValue: raw)

我在放弃之前就解决了这个问题。我不认为有关于它的文档，但它确实有效。