Good practices using forms - symfony

Question

I have to change a web that is using different types to generate forms. There is in Bundle/Form/ folder 2 files:
ProductType.php
ProductEditType.php
It's working fine, the first one is used to generate the new product form and the second one the form to edit it.
Almost 95% of both files is the same, so I guess it has to exist any way to use one type to generate more than one form.
I have been reading about how to modify forms using form events, but I have not found clearly what is the general good practice about it.
Thanks a lot.
Update
I wrote an Event Subscriber as follows.
<?php
namespace Project\MyBundle\Form\EventListener;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
/**
* Description of ProductTypeOptionsSubscriber
*
* #author Javi
*/
class ProductTypeOptionsSubscriber implements EventSubscriberInterface
{
public static function getSubscribedEvents() {
return array(FormEvents::PRE_SET_DATA => 'preSetData');
}
public function preSetData(FormEvent $event){
$data = $event->getData();
$form = $event->getForm();
if( !$data || !$data->getId() ){
// No ID, it's a new product
//.... some code for other options .....
$form->add('submit','submit',
array(
'label' => 'New Produtc',
'attr' => array('class' => 'btn btn-primary')
));
}else{
// ID exists, generating edit options .....
$form->add('submit','submit',
array(
'label' => 'Update Product',
'attr' => array('class' => 'btn btn-primary')
));
}
}
}
In ProductType, inside buildForm:
$builder->addEventSubscriber(new ProductTypeOptionsSubscriber());
So that's all, it was very easy to write and it works fine.

Answer 1

You can read this cookbook event subscriber, the first scenario can do for you.
Returning to the example of the documentation..
Add the fields that you want them to being modified in this way:
$builder->addEventSubscriber(new AddNameFieldSubscriber());
Then create the event event subscriber by entering your logic:
// src/Acme/DemoBundle/Form/EventListener/AddNameFieldSubscriber.php
namespace Acme\DemoBundle\Form\EventListener;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
class AddNameFieldSubscriber implements EventSubscriberInterface
{
public static function getSubscribedEvents()
{
// Tells the dispatcher that you want to listen on the form.pre_set_data
// event and that the preSetData method should be called.
return array(FormEvents::PRE_SET_DATA => 'preSetData');
}
public function preSetData(FormEvent $event)
{
$data = $event->getData();
$form = $event->getForm();
// check if the product object is "new"
// If you didn't pass any data to the form, the data is "null".
// This should be considered a new "Product"
if (!$data || !$data->getId()) {
$form->add('name', 'text');
....
..... // other fields
}
}
}