IOS Swift2 push view up when showing keyboard and prevent black screen while navigating inside keyboard panel

override func viewDidLoad() {
        super.viewDidLoad()


        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.keyboardWillShow), name: UIKeyboardWillShowNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.keyboardWillHide), name: UIKeyboardWillHideNotification, object: nil)

    }


    func keyboardWillShow(notification: NSNotification) {

        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {

// below condition will prevent black screen
            if self.view.frame.origin.y >= 0{
               self.view.frame.origin.y -= keyboardSize.height
            }
        }

    }

    func keyboardWillHide(notification: NSNotification) {
        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.CGRectValue() {
            self.view.frame.origin.y += keyboardSize.height
        }
    }