Keyboard appearing action - ios

Question

I'm trying to make a UIView with UITextField and UIButton in it - like chat applications.
I want to detect level of keyboard appearing on the screen and change UIView height-constraint depending on it.
How can I do this?
Now I have this
#IBOutlet weak var messageTextField: UITextField!
#IBOutlet weak var bottomBarConstrains: NSLayoutConstraint!
override func viewDidLoad()
{
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name:UIKeyboardWillShowNotification, object: nil);
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name:UIKeyboardWillHideNotification, object: nil);
}
override func didReceiveMemoryWarning()
{
super.didReceiveMemoryWarning()
}
#IBAction func sendAction(sender: AnyObject)
{
messageTextField.resignFirstResponder();
}
func keyboardWillShow(notification: NSNotification)
{
var info = notification.userInfo!
let keyboardFrame: CGRect = (info[UIKeyboardFrameEndUserInfoKey] as! NSValue).CGRectValue()
let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! Double
UIView.animateWithDuration(duration, delay: 2, options: UIViewAnimationOptions.CurveEaseIn, animations:
{ () -> Void in
self.bottomBarConstrains.constant = keyboardFrame.size.height;
},
completion: nil);
}
func keyboardWillHide(notification: NSNotification)
{
var info = notification.userInfo!
let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! Double
UIView.animateWithDuration(duration, animations: { () -> Void in
self.bottomBarConstrains.constant = 0;
})
}
But it happens without animation

Answer 1

If you are animating changed constraints you will need to use layoutIfNeeded method on the view that uses that constraint. This method forces view to change layout subviews, but only if it needs it. Since constraint changes does not automatically force view position to change, you need to call this method. So, if your messageTextView is subview of self.view use:
self.bottomBarConstrains.constant = keyboardFrame.size.height
UIView.animateWithDuration(duration, delay: 2, options: .CurveEaseIn, animations: {
self.view.layoutIfNeeded()
}, completion: nil);

Answer 2

Change the code of KeyBoard Open and Hide as below, Remove Delay when open KeyBoard,
func keyboardWillShow(notification: NSNotification)
{
var info = notification.userInfo!
let keyboardFrame: CGRect = (info[UIKeyboardFrameEndUserInfoKey] as! NSValue).CGRectValue()
let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! Double
self.bottomBarConstrains.constant = keyboardFrame.size.height
UIView.animateWithDuration(duration, animations: { () -> Void in
self.messageTextField.layoutIfNeeded()
self.view.layoutIfNeeded()
})
}
func keyboardWillHide(notification: NSNotification)
{
var info = notification.userInfo!
let duration = info[UIKeyboardAnimationDurationUserInfoKey] as! Double
self.bottomBarConstrains.constant = 0;
UIView.animateWithDuration(duration, animations: { () -> Void in
self.messageTextField.layoutIfNeeded()
self.view.layoutIfNeeded()
})
}
Output :