Get variable value in Symfony2 FormBuilder - forms

Question

I am building a form in Symfony2 and for some rows I want to pass a formatted version of each widget's value as a title attribute which I can then display in another div.
If I have not set a formatted version, I will just insert the actual, non-formatted value into the div instead.
Ideally, my twig code might look like this:
{% block form_row %}
{% spaceless %}
<div class="field-display-value">
{% if attr['title'] is defined %}
{{ attr['title'] }}
{% else %}
{{ form.vars.value }}
{% endif %}
</div>
<div class="field-widget">
{{ form_widget(form) }}
</div>
{% endspaceless %}
{% endblock form_row %}
But I don't know how I can access the value of the widget in the formBuilder. Ideally I would like something like this:
$builder->add('some_field', 'text', array(
'attr' => array('title' => someFormattingFunction( this.widget.value ),
));
Obviously, this.widget.value pseudocode doesn't work.
Don't know if even possible, but I don't want to have to resort to javascript madness.
Any ideas?

Answer 1

See this documentation :
http://symfony.com/doc/current/cookbook/form/dynamic_form_modification.html#dynamic-generation-for-submitted-forms
You have to set a listener for the PRE_SET_DATA event, on your formBuilder.
Then you will be able to access the data passed to this form with :
$data = $event->getData();
Now you juste have to add your fields inside.
/!\ Your fields will only be added, if an object is passed to the form.
So if you still want the fields when there is no data passed, you have to add the fields outside the event lister function, and then modify the fields attribute title inside this function.
$form = $event->getForm();
$form->add('some_field', 'text', array(
'attr' => array('title' => someFormattingFunction($data.getSomething()),
));