Swift implementation of Soroush Khanlou's keyboard manager view controller

KeyboardManagerViewController.swift

extension UIEdgeInsets {
    static var zero: UIEdgeInsets {
        return UIEdgeInsetsZero
    }
}

// Inspired by "Many Controllers Make Light Work" by Soroush Khanlou
// http://khanlou.com/2016/02/many-controllers/
class KeyboardManagerViewController: UIViewController {
    let scrollView: UIScrollView
    let center = NSNotificationCenter.defaultCenter()
    var oldInsets: UIEdgeInsets = UIEdgeInsets.zero

    init(scrollView: UIScrollView) {
        self.scrollView = scrollView
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.alpha = 0.0
    }

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

        center.addObserver(self, selector: "keyboardAppeared:", name:UIKeyboardDidShowNotification, object: nil)
        center.addObserver(self, selector: "keyboardDisappeared:", name:UIKeyboardWillHideNotification, object: nil)
    }

    override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)

        center.removeObserver(self, name:UIKeyboardDidShowNotification, object: nil)
        center.removeObserver(self, name:UIKeyboardWillHideNotification, object: nil)
    }

    // Inspired by https://github.com/irace/BRYParseKeyboardNotification
    typealias KeyboardNotificationInfo = (duration: NSTimeInterval, height: CGFloat, animationOptions: UIViewAnimationOptions)
    func parseKeyboardNotification(notification: NSNotification) -> KeyboardNotificationInfo? {
        guard let userInfo = notification.userInfo else { return nil }

        guard let duration: NSTimeInterval = userInfo[UIKeyboardAnimationDurationUserInfoKey]?.doubleValue else { return nil }

        // Convert animation curve to animation options: https://devforums.apple.com/message/878410#878410
        guard let optionsInteger = userInfo[UIKeyboardAnimationCurveUserInfoKey]?.unsignedIntegerValue else { return nil }
        let options = UIViewAnimationOptions(rawValue: optionsInteger << 16)

        guard let keyboardFrame = userInfo[UIKeyboardFrameEndUserInfoKey]?.CGRectValue else { return nil }

        return (duration: duration, height: keyboardFrame.height, animationOptions: options)
    }

    func keyboardAppeared(notification: NSNotification) {
        guard let info = parseKeyboardNotification(notification) else { return }

        oldInsets = scrollView.contentInset
        let newInsets = UIEdgeInsets(top: oldInsets.top, left: 0, bottom: info.height, right: 0)
        scrollView.contentInset = newInsets
        scrollView.scrollIndicatorInsets = newInsets
    }

    func keyboardDisappeared(notification: NSNotification) {
        scrollView.contentInset = oldInsets
        scrollView.scrollIndicatorInsets = oldInsets
    }
}