UITextField-Bottom-Border.swift

extension UITextField {
  func useUnderline() -> Void {
    let border = CALayer()
    let borderWidth = CGFloat(2.0) // Border Width
    border.borderColor = UIColor.red.cgColor
    border.frame = CGRect(origin: CGPoint(x: 0,y :self.frame.size.height - borderWidth), size: CGSize(width: self.frame.size.width, height: self.frame.size.height))
    border.borderWidth = borderWidth
    self.layer.addSublayer(border)   
    self.layer.masksToBounds = true
  }
}