title: Flutter TextEditingController listener being triggered when TextField is focused
body: <p>I have a TextField that has a controller that has a listener for changes. Like this:</p>
  
  <pre><code>final TextEditingController _oneController = TextEditingController();
  </code></pre>
  
  <pre><code>  @override
    void initState() {
      super.initState();
      _oneController.addListener(_listener);
    }
  </code></pre>
  
  <pre><code>TextField(
    controller: _oneController,
  ),
  </code></pre>
  
  <p>Where <code>_listener</code> is a function that will dispatch an event that my form has been edited. </p>
  
  <p>This works fine, but whenever you focus on the TextField it triggers this listener to run, even if no changes were made to the text in the field. </p>
  
  <p>Is there a way to stop my listener from being called when the TextField enters focus? I don't want my listener to be called when there are no changes made to the text in my TextField.</p>