Change the url associated with cancel button - prestashop

Question

I want to change the URL of cancel button presently on canceling the page it is showing me the list but I want to redirect the user on the cancel button.
public function renderForm() {
$this->fields_form = array(
'legend' => array('title' => $this->l('Additional Service'), 'icon' => 'icon-cogs'),
'input' => array(
array(
'type' => 'text',
'label' => $this->l('id_citydelivery'),
'name' => 'id_citydelivery',
'size' => 255),
array(
'type' => 'text',
'label' => $this->l('Service_name'),
'name' => 'service_name',
'size' => 255,
'required' => true,
'desc' => $this->l('Enter name of Arrival port')
),
array(
'type' => 'switch',
'label' => $this->l('Active'),
'name' => 'active',
'required' => false,
'is_bool' => true,
'values' => array(array(
'id' => 'active_on',
'value' => 1,
'label' => $this->l('Active')), array(
'id' => 'active_off',
'value' => 0,
'label' => $this->l('Inactive')))),
),
'submit' => array('title' => $this->l('Save')),
);
return parent::renderForm();
}

Answer 1

After Diving into the code I came to know back button URL is set it by $_post['Back']
So I have overridden it; you have to change # with your URL
public function postProcess() {
if (Tools::getIsset('submitAddadditional_service')) {
$this->redirect_after = Context::getContext()->link->getAdminLink('AdminGCardeliverycity', true) . '&updatecitydelivery&id_citydelivery=' . Tools::getValue('id_citydelivery');
} else {
$_POST['back'] = '#'; //For Cancel button url on form which is genrated by renderform()
}
parent::postProcess();
}