title: get value of checkbox in symfony
body: <p>I want to get the value of checkbox (checked or not), but the checkedbox not added to the form type. this is an example</p>
  
  <pre><code>&lt;input type="checkbox" class="checkbox" id="smsflash"&gt;
  </code></pre>
  
  <p>I ask if there are a possibility to get the value of the checkedbox in the controller or not, and how?</p>