Passing EL method expression as attribute of custom Facelets tagfile - jsf

Question

I created a custom JSF tag:
<ui:composition>
<h:panelGroup>
<rich:dataScroller id="#{id}" for="#{table}" execute="#{table}"
page="#{scrollerPage}" render="#{table}-sc1" maxPages="5"
fastControls="hide" oncomplete="#{onCompl}" scrollListener="#{scrollListenerBean[scrollListenerMethod]}" />
<h:inputText value="#{scrollerPage}" id="#{table}-sc1" size="2">
<f:convertNumber integerOnly="true" />
</h:inputText>
<h:outputText styleClass="outputText"
value=" of #{scrollPagesCount} " />
<h:commandButton value="GO! " />
</h:panelGroup>
</ui:composition>
To pass the listener method, I used the solution suggested in a quite old blog:
<my:dataScroller id="idDS1" table="table1"
scrollerPage="#{bean.navigationHelper.scrollerPage}"
scrollPagesCount="#{bean.navigationHelper.scrollPagesCount}"
onCompl="initForm();"
scrollListenerBean="#{bean}"
scrollListenerMethod="aMethod" />
My questions are: is this the best way to do this? How can I make the method optional?
Thanks a lot for any Help! bye!

Answer 1

My questions are: is this the best way to do this?
That's the only way anyway, provided that you can only use standard JSF/EL facilities and you cannot create a custom taghandler.
You could however create a custom taghandler to convert the value expression to a method expression. The OmniFaces JSF utility library has a <o:methodParam> for exactly this purpose. See also the <o:methodParam> demo page.
You could then end up like:
<my:dataScroller ... scrollListener="#{bean.aMethod}" />
and
<o:methodParam name="scrollListenerMethod" value="#{scrollListener}" />
<rich:dataScroller ... scrollListener="#{scrollListenerMethod}" />
See also:
Dynamic ui include and commandButton
How can I make the method optional?
Theoretically, you could use JSTL tags to build the view conditionally. Something like:
<h:someComponent>
<c:if test="#{not empty fooAttribute}">
<f:attribute name="foo" value="#{fooAttriubte}" />
</c:if>
</h:someComponent>
But that's in the particular case of a special method expression listener attribute unfortunately not possible. There's no such thing as <rich:scrollListener> or something which allows you binding a RichFaces specific scrollListener as a separate tag to the <rich:dataScroller>. Best what you could do without creating custom taghandlers is duplicating the whole <rich:dataScroller> in two <c:if>s (or a <c:choose>); one with and other without scrollListener. This is too clumsy. You'd really better create a custom <my:richScrollListener> taghandler for this which you could then place in a <c:if>.