Order custom fields to be printed on an Invoice

$fieldsClass = hikashop_get('class.field');
						$fields = $fieldsClass->getFields('backend',$this->order,'order');
						if(!empty($fields)){
							foreach($fields as $fieldName => $oneExtraField) {
							?>
								<tr>
									<td class="key">
										<?php echo $this->fieldsClass->getFieldName($oneExtraField);?>
									</td>
									<td>
										<?php echo $this->fieldsClass->show($oneExtraField,@$this->order->$fieldName); ?>
									</td>
								</tr>
							<?php
							}?>
							<?php
						}