a4j：commandButton找不到它的形式

Question

我有以下代码：

<h:form id="dispSchedule">
  <a4j:commandButton value="View Full Schedule" 
                     rendered="#{studentClassView.dispClass.getBoolean('class_publish_loc')}"
                     render ="@form"
                     action="#{studentClassView.toggleDisplaySchedule()}"/>
  <rich:extendedDataTable id="fullSchedule" 
    ...
  </rich:extendedDataTable>
</h:form>

当我点击按钮时，会显示extendedDataTable但我收到此消息：

The form component needs to have a UIForm in its ancestry. Suggestion: enclose the necessary components within <h:form>

有关为何无法找到其形式的任何想法？