SomeLiveClass.swift

import UIKit

@IBDesignable
class SomeLiveClass: UIView {
    
    @IBInspectable var placeholder: String = "Default"
    @IBInspectable var fontSize: CGFloat = 20
    @IBInspectable var lineWidth: CGFloat = 1
    @IBInspectable var lineColor: UIColor = UIColor.blackColor()
    
    var textField: UITextField!
    var underline: CAShapeLayer!
}

// MARK: - Lifecycle
extension SomeLiveClass {
    
    override func awakeFromNib() {
        super.awakeFromNib()
        createSubviews()
    }
    
    func createSubviews() {
        // Initialize text field
        textField = UITextField()
        textField.setTranslatesAutoresizingMaskIntoConstraints(false)
        textField.borderStyle = UITextBorderStyle.None
        textField.backgroundColor = UIColor.lightGrayColor()
        textField.placeholder = placeholder
        textField.font = UIFont.systemFontOfSize(fontSize)
        textField.sizeToFit()
        addSubview(textField)
        
        // Deal with Auto Layout
        let views: [NSObject: AnyObject] = ["textField": textField]
        let metrics: [NSObject: AnyObject] = ["lineWidth": lineWidth]
        
        self.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("|[textField]|", options: nil, metrics: metrics, views: views))
        self.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[textField]-(lineWidth)-|", options: nil, metrics: metrics, views: views))
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        // Initialize underline
        if underline != nil {
            underline.removeFromSuperlayer()
        }
        
        underline = CAShapeLayer()
        var bezierPath = UIBezierPath()
        bezierPath.moveToPoint(CGPointMake(0, textField.bounds.height + (lineWidth / 2)))
        bezierPath.addLineToPoint(CGPointMake(bounds.width, textField.bounds.height + (lineWidth / 2)))
        underline.path = bezierPath.CGPath
        underline.strokeColor = lineColor.CGColor
        underline.lineWidth = lineWidth
        layer.addSublayer(underline)
    }
    
    override func intrinsicContentSize() -> CGSize {
        return CGSize(width: UIViewNoIntrinsicMetric, height: textField.bounds.height + lineWidth)
    }
    
    override func prepareForInterfaceBuilder() {
        createSubviews()
    }
}

// MARK: - Methods
extension SomeLiveClass {
    
}

// MARK: - Delegate Methods
extension SomeLiveClass {
    
}

// MARK: - Actions
extension SomeLiveClass {
    
    
}