如何添加渐变?

let gradientLayer = CAGradientLayer()

gradientLayer.frame = self.bounds

gradientLayer.endPoint = CGPointZero

gradientLayer.startPoint = CGPointMake(1, 1)

gradientLayer.colors = [UIColor(rgb: 0xff243e).CGColor,UIColor(rgb: 0xff5c31).CGColor]

self.layer.addSublayer(gradientLayer)

self.addSubview(self.alphaView!)