Retrieves a views field value from the style plugin.
$index: The index count of the row as expected by views_plugin_style::getField().
$field_id: The ID assigned to the required field in the display.
public function getField($index, $field_id) {
if (empty($this->view->style_plugin) || !is_object($this->view->style_plugin) || empty($field_id)) {
return '';
}
return $this->view->style_plugin
->getField($index, $field_id);
}