Animate Gradient使用线性路径查看iOS

Question

我正在尝试连续制作渐变层动画。请看下面的gif？

我正在使用CAGradientLayer，但它一次只能动画颜色。

var gradient: CAGradientLayer!
self.gradient = CAGradientLayer()
self.gradient.frame = CGRect(x: 0, y: 0, width:view.layer.frame.size.width, height: 50)
self.gradient.colors = [UIColor.redColor().CGColor, UIColor.redColor().CGColor]
self.view.layer.addSublayer(self.gradient)
self.animateLayer()

func animateLayer () {
let fromColors: NSArray = self.gradient.colors!
let toColors: NSArray = [UIColor.blueColor().CGColor, UIColor.blueColor().CGColor]
self.gradient.colors = toColors as [AnyObject]
let animation : CABasicAnimation = CABasicAnimation(keyPath: "colors")
animation.fromValue = fromColors
animation.toValue = toColors
animation.duration = 3.00
animation.removedOnCompletion = true
animation.fillMode = kCAFillModeForwards
animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear)
animation.delegate = self
self.gradient?.addAnimation(animation, forKey:"animateGradient")
}