title: Adding space between textfield character when typing in text filed
body: <p>I have a <code>textfield</code> with maximum character range 16, After every 4 characters, I want to add minus character or space and then writing The rest of the characters like this sample 5022-2222-2222-2222. 
  there is my code but that's don't work, how can do this?</p>
  
  <pre><code>if textField.text?.characters.count  == 5 {
  
                 let  l = textField.text?.characters.count
              let attributedString = NSMutableAttributedString(string: cartNumberTextField.text!)
              attributedString.addAttribute(NSKernAttributeName, value: CGFloat(4.0), range: NSRange(location: l!, length: 4))
              cartNumberTextField.attributedText = attributedString
  
              }
  
              else if textField.text?.characters.count  == 9 {
  
                  let  l = textField.text?.characters.count
                  let attributedString = NSMutableAttributedString(string: cartNumberTextField.text!)
                  attributedString.addAttribute(NSKernAttributeName, value: CGFloat(4.0), range: NSRange(location: l!, length: 4))
                  cartNumberTextField.attributedText = attributedString
  
              }
  
              else if textField.text?.characters.count  == 13 {
  
                  let  l = textField.text?.characters.count
                  let attributedString = NSMutableAttributedString(string: cartNumberTextField.text!)
                  attributedString.addAttribute(NSKernAttributeName, value: CGFloat(4.0), range: NSRange(location: l!, length: 4))
                  cartNumberTextField.attributedText = attributedString
  
              }
  </code></pre>
  
  <p>I am adding this code in <code>UITextField</code> <code>shouldChangeCharactersIn</code> range method.</p>