Is it possible to use <c:if> inside <a4j:repeat>

问题

Is it possible to use <c:if> inside <a4j:repeat>?

I need to render a <br /> each 4 elements. I tried the following approach:

<a4j:repeat value="#{MBean.sucursal.events}" var="item" rowKeyVar="idx" >   
   <h:outputText value="#{item.eventDescription}" id="item1" />
   <c: if test=#{idx % 4 == 0}>
       <br />
   </c:if>
</a4j:repeat>

However, it does not render the <br /> elements at all.

How can I achieve the requirement anyway?

回答1:

Note: I'll ignore the careless formulation of the code which causes that it wouldn't compile/run properly at all. There's a space in <c :if> and the quotes are missing from the <c:if test> attribute. In future questions please pay a bit more attention to the properness of the code snippets you post, otherwise you'll only get invalid answers due to those red herrings.

---

Coming back to your concrete problem, this construct will indeed fail. The <c:if> runs during view build time (when the JSF component tree is about to be populated based on Facelets/JSP files), while the <a4j:repeat> runs during view render time (when the HTML code is about to be generated based on the JSF component tree). So, at the moment the <c:if> runs, #{idx} does not exist in the scope at all and always evaluates to null.

There are basically 2 solutions:

1. Use <c:forEach> instead of <a4j:repeat> to iterate over the items. It runs during view build time, so it'll run "in sync" with <c:if>.

   <c:forEach items="#{MBean.sucursal.events}" var="item" varStatus="loop">   
      <h:outputText value="#{item.eventDescription}" id="item#{loop.index}" />
      <c:if test="#{loop.index % 4 == 0}">
          <br />
      </c:if>
   </c:forEach>
   

   (note that I changed the <h:outputText id> as well, otherwise you end up with duplicate component ID errors or malformed HTML; feel free to omit the id attribute altogether, JSF will autogenerate proper one)

2. Use JSF component's rendered attribute instead of <c:if> to conditionally render HTML. It runs during view render time, so it'll run "in sync" with <a4j:repeat>.

   <a4j:repeat value="#{MBean.sucursal.events}" var="item" rowKeyVar="idx">   
      <h:outputText value="#{item.eventDescription}" id="item1" />
      <h:panelGroup rendered="#{idx % 4 == 0}">
          <br />
      </h:panelGroup>
   </a4j:repeat>
   

See also:

• JSTL in JSF2 Facelets... makes sense?

来源：https://stackoverflow.com/questions/13751889/is-it-possible-to-use-cif-inside-a4jrepeat