Symfony2 - 使用ArrayCollection填充文本字段？

I am using the FPNTagBundle and I would like to have a text field to add tags to entities that works in the same way as the one on this site.

I can create a new entity with tags no problem by using explode but when I come to edit the entity again, I get something like this in the text field.

Doctrine\Common\Collections\ArrayCollection@0000000062a07bb50000000047044868

Is there a way I can pre populate a text field with the array collection, so that all of the tags appear, separated by a space?

Here's what I currently have in my controller:

public function editpageAction(Request $request, $id = NULL)
{
    $em = $this->getDoctrine()->getEntityManager();
    $tagManager = $this->get('fpn_tag.tag_manager');
    $page = new Page();

    if ( ! empty($id))
    {
        $page = $em->getRepository('ContentBundle:Page')->findOneById($id);
        $tagManager->loadTagging($page);
    }

    $form = $this->createForm(new PageType(), $page);

    if ($request->isMethod('POST')) 
    {
        $form->bind($request);

        if ($form->isValid()) 
        {   
            $em = $this->getDoctrine()->getManager();
            $em->persist($page);
            $em->flush();

            return $this->redirect($this->generateUrl('content_admin_list_sections'));
        }
    }

    return $this->render('ContentBundle:Admin:page.html.twig', array('form' => $form->createView()));
}

Any advice appreciated.

Thanks

This is what the Data transfomers are made for.

How to use Data Transformers

A simple example:

public function transform($tags)
{
    $tags = $tags->toArray();

    if (count($tags) < 1)
        return '';
    else
        return implode(' ', $tags);
}

public function reverseTransform($string)
{
    $tags = new ArrayCollection();
    $tagsArray = explode(' ', $string);

    if (count($tagsArray) > 0)
        $tags = new ArrayCollection($tagsArray);

    return $tags;
}