Swift 返回一个渐变的 UIImageView

func createGradientLayer(color : UIColor, width : CGFloat, height : CGFloat) -> UIImageView{     let layer : CAGradientLayer = CAGradientLayer ()     let gradientColors: [CGColor] = [color.CGColor, UIColor.whiteColor().CGColor]     let gradientLocations: [CGFloat] = [0.0, 1.0]     layer.colors = gradientColors     layer.locations = gradientLocations     layer.startPoint = CGPointMake(0, 0)     layer.endPoint = CGPointMake(1, 0)     layer.frame = CGRectMake(0, 0, width, height)     let imageView : UIImageView = UIImageView(     imageView.layer.addSublayer(layer)     return imageView}