Adds border, corner radius, and padding to the UITextField. These properties can be set via the attribute inspector in storyboard.

CustomTextField.swift

import UIKit

@IBDesignable
class CustomTextField: UITextField {
    
    var padding: UIEdgeInsets {
        get {
            return UIEdgeInsets(top: 0, left: paddingValue, bottom: 0, right: paddingValue)
        }
    }
    
    override func textRectForBounds(bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }
    
    override func placeholderRectForBounds(bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }
    
    override func editingRectForBounds(bounds: CGRect) -> CGRect {
        return UIEdgeInsetsInsetRect(bounds, padding)
    }
    
    @IBInspectable var paddingValue: CGFloat = 0
    
    
    @IBInspectable var borderColor: UIColor? = UIColor.clearColor() {
        didSet {
            layer.borderColor = self.borderColor?.CGColor
        }
    }
    @IBInspectable var borderWidth: CGFloat = 0 {
        didSet {
            layer.borderWidth = self.borderWidth
        }
    }
    @IBInspectable var cornerRadius: CGFloat = 0 {
        didSet {
            layer.cornerRadius = self.cornerRadius
            layer.masksToBounds = self.cornerRadius > 0
        }
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
    }
    
    override func drawRect(rect: CGRect) {
        self.layer.cornerRadius = self.cornerRadius
        self.layer.borderWidth = self.borderWidth
        self.layer.borderColor = self.borderColor?.CGColor
    }
}

In Swift 4...

import UIKit

@IBDesignable
class CustomTextField: UITextField {
	
	var padding: UIEdgeInsets {
		get {
			return UIEdgeInsets(top: 0, left: paddingValue, bottom: 0, right: paddingValue)
		}
	}
	
	override func textRect(forBounds bounds: CGRect) -> CGRect {
		return UIEdgeInsetsInsetRect(bounds, padding)
	}
	
	override func placeholderRect(forBounds bounds: CGRect) -> CGRect {
		return UIEdgeInsetsInsetRect(bounds, padding)
	}
	
	override func editingRect(forBounds bounds: CGRect) -> CGRect {
		return UIEdgeInsetsInsetRect(bounds, padding)
	}
	
	@IBInspectable var paddingValue: CGFloat = 0
	
	
	@IBInspectable var borderColor: UIColor? = UIColor.clear {
		didSet {
			layer.borderColor = self.borderColor?.cgColor
		}
	}
	
	@IBInspectable var borderWidth: CGFloat = 0 {
		didSet {
			layer.borderWidth = self.borderWidth
		}
	}
	
	@IBInspectable var cornerRadius: CGFloat = 0 {
		didSet {
			layer.cornerRadius = self.cornerRadius
			layer.masksToBounds = self.cornerRadius > 0
		}
	}
	
	required init?(coder aDecoder: NSCoder) {
		super.init(coder: aDecoder)
	}
	
	override init(frame: CGRect) {
		super.init(frame: frame)
	}
	
	override func draw(_ rect: CGRect) {
		self.layer.cornerRadius = self.cornerRadius
		self.layer.borderWidth = self.borderWidth
		self.layer.borderColor = self.borderColor?.cgColor
	}
	
}