ZF2 Select element usage - zend-form

Question

I'm using Zend Framework 2 and I need a Dependent Dropdown. When user select an category (cat_id on my example) the system fills the subcategory (sca_id) with the correct elements.
I could do that by creating an application like this:
My form looks like:
$this->add(array(
'name' => 'cat_id',
'type' => 'Zend\Form\Element\Select',
'options' => array(
'label' => 'Categoria',
'value_options' => array(
'' => '',
),
),
));
$this->add(array(
'name' => 'sca_id',
'type' => 'Zend\Form\Element\Select',
'options' => array(
'label' => 'Sub Categoria',
'style' => 'display:none;', // Esse campo soh eh exibido qndo uma categoria for escolhida
'value_options' => array(
'' => '',
),
),
));
Note that I don't fill the value_options there, because I choose do that in my controller, where the Service Manager is avaliable:
$form = new ProdutoForm('frm');
$form->setAttribute('action', $this->url()->fromRoute('catalogo-admin', array( ... )));
// Alimenta as comboboxes...
$form->get('cat_id')->setValueOptions($this->getCategoriaService()->listarCategoriasSelect());
On the change event of cat_id I do an $.ajax to grab the elements from an Action and fill the sca_id.
That works fine!
The problem is on my validation:
$this->add(array(
'name' => 'cat_id',
'require' => true,
'filters' => array(
array('name' => 'Int'),
),
));
$this->add(array(
'name' => 'sca_id',
'require' => true,
'filters' => array(
array('name' => 'Int'),
),
));
When I submit my form it keeps saying : The input was not found in the haystack for both dropdowns...
What I'm doing wrong?
Extra questions : There's a better way to fill my dropdowns?
Ps.: I guess this question Disable notInArray Validator Zend Framework 2 asks something similar than me, but I wanted to detail more my problem.

Answer 1

Well, I realized that I should populate my select element before validate my form!
// SaveAction
$request = $this->getRequest();
if ($request->isPost())
{
$form = new ProdutoForm();
// Alimenta as comboboxes...
$form->get('cat_id')->setValueOptions($this->getCategoriaService()->listarCategoriasSelect());
$form->get('sca_id')->setValueOptions($this->getSubCategoriaService()->listarSubCategoriasSelect());
// If the form doesn't define an input filter by default, inject one.
$form->setInputFilter(new ProdutoFormFilter());
// Get the data.
$form->setData($request->getPost());
// Validate the form
if ($form->isValid())
{
// Valid!
}else{
// Invalid...
}
That code works nice. My form now validate perfectly!