     }
     
     func subscribeToNotifications() {
-        let center = NSNotificationCenter.defaultCenter()
+        let center = self.notificationCenter
         center.addObserver(self,
                            selector: #selector(onKeyboardDidHide),
                            name: UIKeyboardDidHideNotification,

    public weak var textFieldDelegate: UITextFieldDelegate?
    
    let fields: Array<UITextField>

    /**
     Instantiates `KeyboardController` object.
     
     - parameter field: an `UITextField` object.
     
     - author: Michal Konturek
     */
    convenience public init(field: UITextField) {
        self.init(fields: [field])
    }

    /**
     Instantiates `KeyboardController` object.
     
     - parameter fields: an array of `UITextField` objects.
     
     - author: Michal Konturek
     */
    public init(fields: Array<UITextField>) {
        self.fields = fields
        super.init()

        for field in self.fields {

    }
    
    deinit {
        self.notificationCenter.removeObserver(self)
    }
}

