A single-bordered UITextField

gistfile1.txt

import UIKit

@IBDesignable class SingleBorderedTextField: UITextField {
    
    private var bottomBorder = UIView()
    private (set) var lineStrength: CGFloat = 1
    
    @IBInspectable var lineWidth: CGFloat {
        get {
            return self.lineStrength
        }
        set {
            self.lineStrength = newValue
        }
    }
    
    @IBInspectable var borderColor: UIColor? {
        get {
            return UIColor(cgColor: layer.borderColor!)
        }
        set {
            layer.borderColor = newValue?.cgColor
        }
    }
    
    override func awakeFromNib() {
        
        self.translatesAutoresizingMaskIntoConstraints = false
        self.borderStyle = .none
        
        bottomBorder = UIView.init(frame: CGRect(x: 0, y: 0, width: 0, height: 0))
        bottomBorder.backgroundColor = self.borderColor
        bottomBorder.translatesAutoresizingMaskIntoConstraints = false
        
        addSubview(bottomBorder)
        
        bottomBorder.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        bottomBorder.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
        bottomBorder.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
        bottomBorder.heightAnchor.constraint(equalToConstant: self.lineStrength).isActive = true
        
    }
}