动画TextField在Swift中消失了

import UIKit

class AnimatedTextField: UITextField {
    override func layoutSubviews() {
        super.layoutSubviews()
        
        // 设置初始状态
        self.alpha = 0
        self.transform = CGAffineTransform(translationX: 0, y: -20)
        
        // 执行动画
        UIView.animate(withDuration: 0.5, delay: 0.2, options: .curveEaseInOut, animations: {
            self.alpha = 1
            self.transform = CGAffineTransform.identity
        }, completion: nil)
    }
}

// 在视图控制器中使用动画TextField
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let animatedTextField = AnimatedTextField(frame: CGRect(x: 50, y: 50, width: 200, height: 30))
        animatedTextField.placeholder = "请输入"
        self.view.addSubview(animatedTextField)
    }
}