Callback set_message not working with multidimensional array post - codeigniter

Question

On my codeigniter project my callback is not working as would like with my multidimensional array post
I am trying on my callback set message $key['image'] to display correct value of the multidimensional array post. But when I var dump it returns NULL
On my set rules the multidimensional array validation works.
But for some reason the $key['image'] on my callback function
set_message('banner_image_regex', 'This banner' .' '. $key['image'] .' '. 'image contains a underscore cannot upload file.') not picking up.
Question on my callback function banner_image_regex() how can I make $key['image'] pick up the post value and display it.
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class Banner_add extends MX_Controller {
public function __construct() {
parent::__construct();
}
public function index() {
$data['title'] = "Banner Add";
$this->load->library('form_validation');
$this->form_validation->set_rules('banner_name', 'Banner Name', 'required|callback_validate_form');
$this->form_validation->set_rules('banner_status', 'Banner Status', 'required');
if (!empty($this->input->post('banner_image'))) {
foreach ($this->input->post('banner_image') as $key => $value) {
$this->form_validation->set_rules('banner_image['.$key.'][image]', 'Banner Image', 'callback_banner_image_regex');
}
}
if ($this->form_validation->run($this) == FALSE) {
$this->load->view('template/banner/banner_add', $data);
} else {
redirect('admin/banner/banner_list');
}
}
public function banner_image_regex() {
$banner_image = $this->input->post('banner_image');
foreach ($banner_image as $key => $value) {
if (preg_match('/^[a-z0-9]+$/', $key['image'])) {
return TRUE;
} else {
$this->form_validation->set_message('banner_image_regex', 'This banner' .' '. $key['image'] .' '. 'image contains a underscore cannot upload file.');
return FALSE;
}
}
}
}

Answer 1

Asuming you were following CI specs about naming array fields in form validation,
you are already sending specific value (string/image name) to callback function.
So it need to be like:
public function banner_image_regex($image_name) {
if (preg_match('/^[a-z0-9]+$/', $image_name)) {
return TRUE;
} else {
$this->form_validation->set_message('banner_image_regex', 'This banner' .' '. $image_name .' '. 'image contains a underscore cannot upload file.');
return FALSE;
}
}