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!)