title: Check if form entry is multiple of 10
body: <p>I want to validate a <code>TexFormField</code> field to both check for a min value of 10 (done elsewhere) and also check that the value entered is a multiple of 10.</p>
  
  <p>I've written a function that tries to handle both and it seems to work. However, it feels clunky. And it doesn't provide any feedback until the form is submitted. Here is what I've written:</p>
  
  <pre><code>    final form = _formKey.currentState;
      if ((form.validate()) &amp;&amp; (_amount / 10 is int)) {
        form.save();
        return true;
      }
      return false;
    } 
  </code></pre>
  
  <p>Is there a cleaner way to check if an entered value is a multiple of 10 (or any integer)? For example, in the <code>validator:</code> property field itself?</p>