/**
  * Default constructor for the Commerce Line Item object. Do not call this
  * class directly. Create a separate class for each line item type and use
  * its constructor.
  *
  * You can also pass a second argument, and it will be interpreted as
  * order_id. It is used for creating a new line item.
  *
  * @param int $line_item_id
  *   Product id if an existing product is to be loaded.
  */
 public function __construct($line_item_id = NULL)
 {
     $args = func_get_args();
     array_shift($args);
     $order_id = array_shift($args);
     if (is_null($order_id)) {
         $order_id = 0;
     }
     if (!is_null($line_item_id) && is_numeric($line_item_id)) {
         $line_item = commerce_line_item_load($line_item_id);
         if (!$line_item) {
             $this->setErrors("Line item with id {$line_item_id} does not exist.");
             $this->setInitialized(FALSE);
             return;
         }
     } else {
         $class = new \ReflectionClass(get_called_class());
         $type = Utils::makeSnakeCase($class->getShortName());
         $line_item = commerce_line_item_new($type, $order_id);
     }
     parent::__construct($line_item);
 }
<div class="views-field-title"><?php 
print $fields['title']->content;
?>
</div>

<?php 
$nid = strip_tags($fields['nid']->content);
$node = node_load($nid);
$product = commerce_product_load($node->field_product[LANGUAGE_NONE][0]['product_id']);
?>
<div class="views-field-field-sell-price"><?php 
print commerce_currency_format($product->commerce_price[LANGUAGE_NONE][0]['amount'], 'VND');
?>
</div>

<div class="views-field-field-old-price"><?php 
print $fields['field_old_price']->content;
?>
</div>
<?php 
$line_item = commerce_line_item_new($product->type, $order_id = 0);
$line_item->data['context']['product_ids'] = array($product->product_id);
$line_item->quantity = 1;
$qty = 1;
$form_id = commerce_cart_add_to_cart_form_id(array($product->product_id), $qty);
$addtocart_form = drupal_get_form($form_id, $line_item);
?>
<div class="views-field-view-node "><?php 
print render($addtocart_form);
?>
</div>