title: Disable button in UIAlertView while text field is empty
body: <p>I make an <code>AlertViewController</code> with <code>textField</code> that asks user to type a name of new item for data model. </p>
  
  <p>So I want to keep submit button disabled while text field is empty. In other case, when I create <code>@IBOutlet</code> in <code>ViewController</code> for textfield from storyboard I could just use some methods from <code>UITextFieldDelegate</code> protocol and solve problem without your help.</p>
  
  <p>But now I can't.</p>