gistfile1.php

<?php

namespace Application\FrontendBundle\Controller;

use Symfony\Bundle\FrameworkBundle\Controller;
use Symfony\Components\Form;

class MainController extends Controller
{
    public function indexAction()
    {
        \Symfony\Components\OutputEscaper\Escaper::markClassAsSafe('Symfony\Components\Form\Form');

        $invoice = new Invoice();
        $invoice->lineItems[] = new LineItem();
        $invoice->lineItems[] = new LineItem();

        $form = new Form\Form('invoice', $invoice, $this->container->getValidatorService());
        $form->add(new Form\TextField('property1'));
        $form->add(new Form\TextField('property2'));

        $lineItemGroup = new Form\FieldGroup('lineItems');
        $lineItemGroup->add(new Form\TextField('property1'));
        $lineItemGroup->add(new Form\TextField('property2'));
        $lineItemGroup->add(new Form\TextField('property3'));
        $lineItemGroup->add(new Form\TextField('property4'));
        $collection = new Form\CollectionField($lineItemGroup);        

        $form->add($collection);
        
        if ($this->getRequest()->getMethod() == 'POST')
        {
            $form->bind($this->getRequest()->get('invoice'));

            if ($form->isValid())
            {
                echo '<pre>';
                print_r($invoice);
                echo '</pre>';
                exit('valid');
            }
        }

        return $this->render('FrontendBundle:Main:index', array('form' => $form));
    }
}

class Invoice
{
    public $property1;
    public $property2;
    public $lineItems = array();
}

class LineItem
{
    public $property1;
    public $property2;
    public $property3;
    public $property4;

    public function getTitle()
    {
        return $this->title;
    }

    public function setTitle($title)
    {
        $this->title = $title;
    }
}