Underlined UITextView in Swift - http://purelywebdesign.co.uk/tutorial/swift-underlined-text-field-tutorial

Helpers.swift

extension UITextField {
    
    func underlined(){
        let border = CALayer()
        let width = CGFloat(1.0)
        border.borderColor = UIColor.lightGrayColor().CGColor
        border.frame = CGRect(x: 0, y: self.frame.size.height - width, width:  self.frame.size.width, height: self.frame.size.height)
        border.borderWidth = width
        self.layer.addSublayer(border)
        self.layer.masksToBounds = true
    }
}

// Call with....
yourTextField.underlined()

I read somewhere that bounds property is required. Adding this line worked for me

border.bounds = CGRect(x: 0, y: 0, width:  self.frame.size.width, height: self.frame.size.height)

I have applied this method and it seem working fine but cannot apply all screen device.
let border = CALayer()
let width = CGFloat(1.0)
border.borderColor = UIColor.lightGray.cgColor
border.frame = CGRect(x: 0, y: self.frame.size.height - width, width: self.frame.size.width, height: self.frame.size.height)
border.borderWidth = width
self.layer.addSublayer(border)
self.layer.masksToBounds = true