protected function addAttachment()
{
global $ilUser;
include_once './Services/Calendar/classes/Export/class.ilCalendarExport.php';
$export = new ilCalendarExport();
$export->setExportType(ilCalendarExport::EXPORT_APPOINTMENTS);
$export->setAppointments(array($this->getAppointmentId()));
$export->export();
include_once './Services/Mail/classes/class.ilFileDataMail.php';
$attachment = new ilFileDataMail($this->getSender());
$attachment->storeAsAttachment('appointment.ics', $export->getExportString());
$this->setAttachments(array('appointment.ics'));
}
