keyboardWillShow.swift

func keyboardWillShow(notification: NSNotification) {
    let info = notification.userInfo!
    let rect = (info[UIKeyboardFrameEndUserInfoKey] as! NSValue).CGRectValue()
    let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! Double
    let curve = notification.userInfo![UIKeyboardAnimationCurveUserInfoKey] as! UInt
    let opts = UIViewAnimationOptions(rawValue: curve << 16)
    
    UIView.animateWithDuration(duration, delay: 0, options: opts, animations: {
        self.bottomConstraint.constant = rect.height
        self.view.layoutIfNeeded()
    }) { (finish: Bool) in
        
    }
}