如何在swift中将文本字段的文本置于渐变背景的前面

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建渐变背景视图
        let gradientLayer = CAGradientLayer()
        gradientLayer.frame = view.bounds
        gradientLayer.colors = [UIColor.red.cgColor, UIColor.blue.cgColor]
        gradientLayer.startPoint = CGPoint(x: 0, y: 0)
        gradientLayer.endPoint = CGPoint(x: 1, y: 1)
        view.layer.addSublayer(gradientLayer)
        
        // 创建文本字段
        let textField = UITextField(frame: CGRect(x: 50, y: 200, width: 200, height: 30))
        textField.text = "Hello World"
        textField.font = UIFont.systemFont(ofSize: 16)
        textField.textColor = UIColor.white
        textField.textAlignment = .center
        
        // 将文本字段添加到渐变背景视图的前面
        view.addSubview(textField)
    }
}