title: Get parent object within child formType event
body: <p>I've created two form types as below</p>
  
  <p>EmailOptInType.php</p>
  
  <pre><code>public function buildForm(FormBuilderInterface $builder, array $options)
  {
      $builder
          -&gt;addEventListener(FormEvents::SUBMIT, function (FormEvent $event) {
              $_1 = $event-&gt;getData();
              $_2 = $event-&gt;getForm()-&gt;getData();
              $_3 = $event-&gt;getForm()-&gt;getParent()-&gt;getData();
              $form = $event-&gt;getForm();         
          });
  }
  
  /**
   * @return string
   */
  public function getParent()
  {
      return 'checkbox';
  }
  </code></pre>
  
  <p>And SubscribeType.php</p>
  
  <pre><code>public function buildForm(FormBuilderInterface $builder, array $options)
  {
      $builder
          -&gt;add('email', 'text', array(
              'label'    =&gt; 'Sign up to news',
              'required' =&gt; true,
              'attr'     =&gt; array(
                  'placeholder' =&gt; 'Enter your email to subscribe',
              ),
          ))
          -&gt;add('email_opt_in', 'newsletter_opt_in', array(
              'data'  =&gt; true
          ));
  }
  
  /**
   * @param OptionsResolver $resolver
   */
  public function configureOptions(OptionsResolver $resolver)
  {
      parent::configureOptions($resolver);
  
      $resolver-&gt;setDefaults(array(
          'data_class' =&gt; 'Bundle\Entity\Customer',
      ));
  }
  </code></pre>
  
  <p>As you can see the subscribeType form includes the opt in form. Is it possible to fetch the parent forms data within the event listener of the child form EmailOptInType?</p>
  
  <p>In the snippet above $_1 returns a boolean value of true which represents the checked checkbox, $_2 returns the same and $_3 returns an empty customer object.</p>
  
  <p>Is it possible to get the customer object that has just been created / submitted?</p>