UILabel文字渐变色

extension UIColor {
    static let gradientTextLink: UIColor = {
            let gradientLayer = CAGradientLayer.init(frame: CGRect.init(x: 0, y: 0, width: screenWidth, height: 16), colors: [rgba(104, 104, 167, 1),rgba(159, 32, 87, 1)], startPoint: CGPoint.init(x: 0.5, y: 0), endPoint: CGPoint.init(x: 0.5, y: 1))
        let linkColor = gradientLayer.outputColor() ?? UIColor.red
            return linkColor
        }()
}
extension CAGradientLayer {
    
    public convenience init(frame:CGRect,colors: [UIColor],locations:[NSNumber] = [0,1],startPoint:CGPoint = CGPoint.init(x: 0, y: 0.5),endPoint:CGPoint = CGPoint.init(x: 1, y: 0.5)) {
        //创建渐变层对象
        self.init()
        self.frame = frame
        //将存储的渐变色数组（UIColor类）转变为CAGradientLayer对象的colors数组，并设置该数组为CAGradientLayer对象的colors属性
        var gradientColors: [CGColor] = [];
        for item in colors {
            gradientColors.append(item.cgColor)
        }
        self.colors = gradientColors
        self.locations = locations
        self.startPoint =  startPoint
        self.endPoint =  endPoint
    }
}

extension CALayer {
    open func outputImage() -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(self.frame.size, self.isOpaque, 0)
        guard let currentContext = UIGraphicsGetCurrentContext() else {
            return nil
        }
        self.render(in: currentContext )
        let ouputImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return ouputImage
    }
    
    open func outputColor() -> UIColor? {
        guard let image = self.outputImage() else {
            return nil
        }
        return UIColor.init(patternImage: image)
    }
    
}

self.label.textColor = UIColor.gradientTextLink