title: How can I catch event when a text field is exiting focus (on blur) in Flutter?
body: <p>I look into TextFormField, the fields here isn't what I need:</p>
  <ul>
  <li><code>onChanged</code> (called after each key pressed, I need when the user has already complete and exit the TextFormField focus)</li>
  <li><code>onEditingComplete</code> (called after user press on Done key or similar, but user may exit TextFormField focus without tapping those button)</li>
  <li><code>onSave</code> (called after calling <code>form.save()</code>. But I need to do this after user finish editing, to let user know that the app does &quot;auto-correcting&quot; to what the user entered)</li>
  <li><code>validator</code> (also called on <code>form.validate()</code>, right before <code>form.save()</code>. not what I needed)</li>
  </ul>
  <p>I need that when user exit the focus (dismissing the keyboard or tapping into another text field), I do a processing to let user see that their input is being adjusted and processed to the &quot;correct one&quot;. How can I catch such event?</p>