title: How do I check when a UITextField changes?
body: <p>I am trying to check when a text field changes, equivalent too the function used for textView - <code>textViewDidChange</code> so far I have done this: </p>
  
  <pre><code>  func textFieldDidBeginEditing(textField: UITextField) {
          if self.status.text == "" &amp;&amp; self.username.text == "" {
              self.topRightButton.enabled = false
          } else {   
              self.topRightButton.enabled = true
          }
      }
  </code></pre>
  
  <p>Which kind of works, but the <code>topRightButton</code> is enabled as soon as the text field is pressed on, I want it to be enabled only when text is actually typed in?</p>