How to add variable to header.php controller and use it in header.tpl - opencart2.3

Question

I am creating a custom theme for OpenCart 2.3 and I need to show some additional information in page header (header.tpl). So I added some variable to catalog/controller/common/header.php:
$data['some_var'] = 'some_value';
And then I am trying to use this data in the header.tpl:
<?php echo $this->data['some_var']; ?>
But I am always getting this error:
Notice: Undefined index: some_var in /var/www/store_com/public_html/catalog/view/theme/mystore/template/common/header.tpl on line 133
If I try to use this code:
<?php echo $some_var; ?>
Then I am getting another error:
Notice: Undefined variable: some_var in /var/www/store_com/public_html/catalog/view/theme/mystore/template/common/header.tpl on line 133
And even when I do echo print_r($this->data) in header.tpl I don't even see this variable in $data array.
What am I doing wrong? Please help.
EDIT
Here is the full code of my header.php controller file. I added my custom variable at the very end of the file.
class ControllerCommonHeader extends Controller {
public function index() {
// Analytics
$this->load->model('extension/extension');
$data['analytics'] = array();
$analytics = $this->model_extension_extension->getExtensions('analytics');
foreach ($analytics as $analytic) {
if ($this->config->get($analytic['code'] . '_status')) {
$data['analytics'][] = $this->load->controller('extension/analytics/' . $analytic['code'], $this->config->get($analytic['code'] . '_status'));
}
}
if ($this->request->server['HTTPS']) {
$server = $this->config->get('config_ssl');
} else {
$server = $this->config->get('config_url');
}
if (is_file(DIR_IMAGE . $this->config->get('config_icon'))) {
$this->document->addLink($server . 'image/' . $this->config->get('config_icon'), 'icon');
}
$data['title'] = $this->document->getTitle();
$data['base'] = $server;
$data['description'] = $this->document->getDescription();
$data['keywords'] = $this->document->getKeywords();
$data['links'] = $this->document->getLinks();
$data['styles'] = $this->document->getStyles();
$data['scripts'] = $this->document->getScripts();
$data['lang'] = $this->language->get('code');
$data['direction'] = $this->language->get('direction');
$data['name'] = $this->config->get('config_name');
if (is_file(DIR_IMAGE . $this->config->get('config_logo'))) {
$data['logo'] = $server . 'image/' . $this->config->get('config_logo');
} else {
$data['logo'] = '';
}
$this->load->language('common/header');
$data['text_home'] = $this->language->get('text_home');
// Wishlist
if ($this->customer->isLogged()) {
$this->load->model('account/wishlist');
$data['text_wishlist'] = sprintf($this->language->get('text_wishlist'), $this->model_account_wishlist->getTotalWishlist());
} else {
$data['text_wishlist'] = sprintf($this->language->get('text_wishlist'), (isset($this->session->data['wishlist']) ? count($this->session->data['wishlist']) : 0));
}
$data['text_shopping_cart'] = $this->language->get('text_shopping_cart');
$data['text_logged'] = sprintf($this->language->get('text_logged'), $this->url->link('account/account', '', true), $this->customer->getFirstName(), $this->url->link('account/logout', '', true));
$data['text_account'] = $this->language->get('text_account');
$data['text_register'] = $this->language->get('text_register');
$data['text_login'] = $this->language->get('text_login');
$data['text_order'] = $this->language->get('text_order');
$data['text_transaction'] = $this->language->get('text_transaction');
$data['text_download'] = $this->language->get('text_download');
$data['text_logout'] = $this->language->get('text_logout');
$data['text_checkout'] = $this->language->get('text_checkout');
$data['text_category'] = $this->language->get('text_category');
$data['text_all'] = $this->language->get('text_all');
$data['home'] = $this->url->link('common/home');
$data['wishlist'] = $this->url->link('account/wishlist', '', true);
$data['logged'] = $this->customer->isLogged();
$data['account'] = $this->url->link('account/account', '', true);
$data['register'] = $this->url->link('account/register', '', true);
$data['login'] = $this->url->link('account/login', '', true);
$data['order'] = $this->url->link('account/order', '', true);
$data['transaction'] = $this->url->link('account/transaction', '', true);
$data['download'] = $this->url->link('account/download', '', true);
$data['logout'] = $this->url->link('account/logout', '', true);
$data['shopping_cart'] = $this->url->link('checkout/cart');
$data['checkout'] = $this->url->link('checkout/checkout', '', true);
$data['contact'] = $this->url->link('information/contact');
$data['telephone'] = $this->config->get('config_telephone');
// Menu
$this->load->model('catalog/category');
$this->load->model('catalog/product');
$data['categories'] = array();
$categories = $this->model_catalog_category->getCategories(0);
foreach ($categories as $category) {
if ($category['top']) {
// Level 2
$children_data = array();
$children = $this->model_catalog_category->getCategories($category['category_id']);
foreach ($children as $child) {
$filter_data = array(
'filter_category_id' => $child['category_id'],
'filter_sub_category' => true
);
$children_data[] = array(
'name' => $child['name'] . ($this->config->get('config_product_count') ? ' (' . $this->model_catalog_product->getTotalProducts($filter_data) . ')' : ''),
'href' => $this->url->link('product/category', 'path=' . $category['category_id'] . '_' . $child['category_id'])
);
}
// Level 1
$data['categories'][] = array(
'name' => $category['name'],
'children' => $children_data,
'column' => $category['column'] ? $category['column'] : 1,
'href' => $this->url->link('product/category', 'path=' . $category['category_id'])
);
}
}
$data['language'] = $this->load->controller('common/language');
$data['currency'] = $this->load->controller('common/currency');
$data['search'] = $this->load->controller('common/search');
$data['cart'] = $this->load->controller('common/cart');
// For page specific css
if (isset($this->request->get['route'])) {
if (isset($this->request->get['product_id'])) {
$class = '-' . $this->request->get['product_id'];
} elseif (isset($this->request->get['path'])) {
$class = '-' . $this->request->get['path'];
} elseif (isset($this->request->get['manufacturer_id'])) {
$class = '-' . $this->request->get['manufacturer_id'];
} elseif (isset($this->request->get['information_id'])) {
$class = '-' . $this->request->get['information_id'];
} else {
$class = '';
}
$data['class'] = str_replace('/', '-', $this->request->get['route']) . $class;
} else {
$data['class'] = 'common-home';
}
//CUSTOM THEME VARIABLES BEGIN
$data['some_var'] = 'some_value';
//CUSTOM THEME VARIABLES END
return $this->load->view('common/header', $data);
}
}

Answer 1

I need to see your controller to get the full picture and then i will give you the full answer, but take a look on your controller and make sure that you bind your data like the sample below:
if (file_exists(DIR_TEMPLATE . $this->config->get('config_template') . '/template/common/header.tpl')) {
return $this->load->view($this->config->get('config_template') . '/template/common/header.tpl', $data);
} else {
return $this->load->view('default/template/common/header.tpl', $data);
}
Thanks

Answer 2

I finally found the solution of my problem, but I am not sure if it is the right way to do this. I found that I need to make changes in system/storage/modification/catalog/controller/common/header‌​.php. It seems like after installing some extension via Vqmod the controller file have been copied to this folder. If I add my variables there then I can access them without any issues.