MAC address text field formatter for UITextField

TextFieldMacAddress.swift

//
//  TextFieldMacAddress.swift
//
//  Created by Peter Mukhortov on 01/11/2015.
//  Copyright © 2015 Peter Mukhortov. All rights reserved.
//
//  MAC address text field formatter for UITextField
//

import Foundation
import UIKit

class TextFieldMacAddress: UITextField {

	override func awakeFromNib() {
		super.awakeFromNib()

		self.addTarget(self, action: "textFieldResetStyles", forControlEvents: UIControlEvents.EditingDidBegin)
		self.addTarget(self, action: "didEndEditing", forControlEvents: UIControlEvents.EditingDidEnd)
		self.addTarget(self, action: "formatMacAddress", forControlEvents: UIControlEvents.EditingChanged)
	}

	func textFieldIsValid() {
		self.textColor = UIColor.greenColor()
	}

	func textFieldIsInvalid() {
		self.textColor = UIColor.redColor()
	}

	func textFieldResetStyles() {
		self.textColor = UIColor.blackColor()
	}

	func didEndEditing() {
		if isValid() {
			textFieldIsValid()
		} else {
			textFieldIsInvalid()
		}
	}

	func isValid() -> Bool {
		let macRegex = "([0-9A-Fa-f]{2}[:]){5}([0-9A-Fa-f]{2})"
		if let macTest = NSPredicate(format: "SELF MATCHES %@", macRegex) as NSPredicate! {
			return macTest.evaluateWithObject(self.text)
		}
		return false
	}

	func formatMacAddress() {
		let stringMaxLength = 12
		var string = self.text!.stringByReplacingOccurrencesOfString("[^0-9A-Fa-f]", withString: "", options: .RegularExpressionSearch)
		var formattedString = String()

		if string.characters.count > stringMaxLength {
			string = string.substringToIndex(string.startIndex.advancedBy(stringMaxLength))
		}

		for char in string.characters {
			if (formattedString.characters.count + 1) % 3 == 0 {
				formattedString.appendContentsOf(":")
			}
			formattedString.append(char)
		}

		self.text = formattedString
	}
}