为什么textField的底边线显示为一半？

Question

我的UIViewController中有5个textFields，我必须在这些所有textFields上显示底部边框线。

我正在使用FloatLabelTextField类，并尝试通过编程方式在每个textField上设置底部边框，但第一次（在viewDidLoad方法中）边框线只显示一半。我不知道为什么会这样。

这是我的代码：

import UIKit

class ViewController: UITableViewController {

    @IBOutlet var vwName: FloatLabelTextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        vwName.delegate = self
        setBottomBorder(textField: vwName, width: 0.8, color: .darkGray)
    }
}

extension ViewController : UITextFieldDelegate {
    func textFieldDidBeginEditing(_ textField: UITextField) {
        if let sublayers = textField.layer.sublayers {
            for layer: CALayer in sublayers  {
                if layer.name == "BottomBorder" {
                    layer.removeFromSuperlayer()
                }
            }
        }
        setBottomBorder(textField: textField, width: 0.8, color: .blue)
    }

    func textFieldDidEndEditing(_ textField: UITextField) {
        if let sublayers = textField.layer.sublayers {
            for layer: CALayer in sublayers  {
                if layer.name == "BottomBorder" {
                    layer.removeFromSuperlayer()
                }
            }
        }
        setBottomBorder(textField: textField, width: 0.8, color: .lightGray)
        textField.resignFirstResponder()
    }

    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }
}

extension ViewController {
    func setBottomBorder(textField: UITextField, width: CGFloat, color: UIColor) {
        let border = CALayer()
        border.name = "BottomBorder"
        border.borderColor = color.cgColor
        border.frame = CGRect(x: 0, y: textField.frame.size.height - width, width: textField.frame.size.width, height: width)
        border.borderWidth = width
        textField.borderStyle = UITextBorderStyle.none
        textField.layer.addSublayer(border)
        textField.layer.masksToBounds = true
    }
}  

如果我点击文字字段，那么边框线就会正常显示。我的意思是当TextFieldDidBeginEditing委托方法调用时边界线显示正确。

但最初在查看加载时它会显示一半。