title: How to know when user delete the input in VerificationCodeInput Flutter
body: <p>I want to make a verification code input in my app. I'm using <a href="https://flutterawesome.com/a-flutter-package-that-help-you-create-a-verification-input/" rel="nofollow noreferrer">this widget</a> to do that. But I don't know how to detect if the user delete the number that he/she inputted after he fully input in the widget so I can disable my submit button. I did the following. How can I know whether the user delete the number he/she inputted after he/she fully input in the field? Thanks!</p>
  
  <pre><code>VerificationCodeInput(
   keyboardType: TextInputType.number,
   length: 4,
   onCompleted: (String value) {
    setState(() {
     full = true;
    });
   },
  ),
  </code></pre>