Workaround for Issue #2059 in Symfony 2.0

NumberToStringTransformer.php

<?php
namespace Acme\HelloBundle\Form\DataTransformer;

use Symfony\Component\Form\DataTransformerInterface;
use Symfony\Component\Form\Exception\UnexpectedTypeException;
use Symfony\Component\Form\Exception\TransformationFailedException;

/**
 * A simple number transformer that allows either comma or dot as decimal separator.
 *
 * Caution: this transformer does not understand thousands separators.
 *
 * @see https://github.com/symfony/symfony/pull/2119
 * @see https://github.com/symfony/symfony/issues/2059
 * @see http://stackoverflow.com/questions/12026050/how-to-create-a-number-field-that-accepts-numbers-with-comma-or-period-in-symfon
 *
 */
class NumberToStringTransformer implements DataTransformerInterface
{
    /**
     * @param mixed $value
     * @return string
     * @throws \Symfony\Component\Form\Exception\UnexpectedTypeException
     */
    public function transform($value)
    {
        if (null === $value) {
            return '';
        }

        if (!is_numeric($value)) {
            throw new UnexpectedTypeException($value, 'numeric');
        }

        return (string)$value;
    }

    /**
     * @param mixed $value
     * @return float|mixed|null
     * @throws \Symfony\Component\Form\Exception\UnexpectedTypeException
     * @throws \Symfony\Component\Form\Exception\TransformationFailedException
     */
    public function reverseTransform($value)
    {
        if (!is_string($value)) {
            throw new UnexpectedTypeException($value, 'string');
        }

        if ('' === $value) {
            return null;
        }

        $value = str_replace(',', '.', $value);

        if (is_numeric($value)) {
            $value = (float)$value;
        } else {
            throw new TransformationFailedException('not a number');
        }

        return $value;
    }
}

NumberType.php

<?php
namespace Acme\HelloBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;

/**
 *
 */
class NumberType extends AbstractType
{
    /**
     * @param \Symfony\Component\Form\FormBuilder $builder
     * @param array $options
     */
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder->appendClientTransformer(new DataTransformer\NumberToStringTransformer());
    }

    /**
     * @param array $options
     * @return string
     */
    public function getParent(array $options)
    {
        return 'field';
    }

    /**
     * @return string
     */
    public function getName()
    {
        return 'calculator_number';
    }

}