在6个设备以下的iPhone中未显示TextField边框

Question

我已经创建了文本字段的底部边框，该边框在所有6或更高版本的设备上均显示，但在6以下则不显示..它显示了我在5s上测试过的空占位符

我正在使用此代码

func designTextfields(){

    let border = CALayer()
    let width = CGFloat(2.0)
    border.borderColor = UIColor.darkGray.cgColor
    border.frame = CGRect(x: 0, y: emailField.frame.size.height - width, width:  emailField.frame.size.width, height: emailField.frame.size.height)

    border.borderWidth = width
    emailField.layer.addSublayer(border)
    emailField.layer.masksToBounds = true


    let border1 = CALayer()
    let width1 = CGFloat(2.0)
    border1.borderColor = UIColor.darkGray.cgColor
    border1.frame = CGRect(x: 0, y: passField.frame.size.height - width1, width:  passField.frame.size.width, height: passField.frame.size.height)

    border1.borderWidth = width1
    passField.layer.addSublayer(border1)
    passField.layer.masksToBounds = true

}