Swift - UI按钮阴影渐变

import UIKit

class GradientButton: UIButton {
    override func layoutSubviews() {
        super.layoutSubviews()
        
        let gradientLayer = CAGradientLayer()
        gradientLayer.frame = bounds
        gradientLayer.colors = [UIColor.red.cgColor, UIColor.blue.cgColor]
        gradientLayer.startPoint = CGPoint(x: 0, y: 0)
        gradientLayer.endPoint = CGPoint(x: 1, y: 1)
        
        layer.insertSublayer(gradientLayer, at: 0)
        
        layer.cornerRadius = bounds.height / 2
        layer.shadowColor = UIColor.black.cgColor
        layer.shadowOpacity = 0.5
        layer.shadowOffset = CGSize(width: 0, height: 2)
        layer.shadowRadius = 4
    }
}