NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)

func keyboardWillShow(notification:NSNotification) {
    let userInfo:NSDictionary = notification.userInfo!
    let keyboardFrame:NSValue = userInfo.valueForKey(UIKeyboardFrameEndUserInfoKey) as! NSValue
    let keyboardRectangle = keyboardFrame.CGRectValue()
    let keyboardHeight = keyboardRectangle.height
}