private function getUploadUrl()
 {
     global $ilCtrl;
     // return null when the form is used
     if ($this->use_form) {
         return null;
     }
     // check if supported
     if (!ilFileUploadUtil::isUploadSupported()) {
         return false;
     }
     // build upload URL
     include_once "Modules/File/classes/class.ilObjFileGUI.php";
     $ilCtrl->setParameterByClass(self::FILE_OBJ_GUI_CLASS, "ref_id", $this->ref_id);
     $ilCtrl->setParameterByClass(self::FILE_OBJ_GUI_CLASS, "new_type", "file");
     return $ilCtrl->getFormActionByClass(self::FILE_OBJ_GUI_CLASS, "uploadFiles", "", true, false);
 }