Using f:selectItems var in passtrough attribute

问题

can I pass expressions to JSF 2 passthrough-attributes? the following code is not working. expression #{country.isoCode} is not evaluated.

<h:selectOneMenu value="#{bean.selectedCountry}" styleClass="selectlist">
   <f:selectItems 
            value="#{bean.countries}" var="country"
            itemLabel="#{country.countryName}" 
            pt:data-icon="flag flag-#{country.isoCode}"/>                
</h:selectOneMenu>

I am using namespace

xmlns:pt="http://xmlns.jcp.org/jsf/passthrough"

and bootstrap-select. attribute "data-icon" is used to show an image. see:

http://silviomoreto.github.io/bootstrap-select/#data-icon

rendered output:

<i class="glyphicon flag flag-"></i> 

回答1:

EL is basically supported/evaluated over all place in a Facelet template. Also outside tags/attributes. Even in HTML comments, where many starters then fall over. So that's not the problem.

Your particular case is, unfortunately, "by design". Before rendering the first <option> element, the <f:selectItems> is is wholly parsed only once and turned into an iterator during which all EL expressions will be evaluated. Then, the component will iterate over it while rendering <option> elements during which all passthrough attributes will be evaluated. However, as the var was already evaluated during creating the iterator, it isn't available anywhere during rendering the passthrough attributes and ultimately evaluates to an empty string.

Fixing that would require quite some changes in standard JSF implementation of <f:selectItems>. I'm not sure if JSF guys would be all ears for that, but you can always try to create an issue.

You can work around this by creating physically multiple <f:selectItem> instances during view build time, with help of <c:forEach>.

<h:selectOneMenu ...>
    <c:forEach items="#{bean.countries}" var="country">
        <f:selectItem 
            itemValue="#{country}" 
            itemLabel="#{country.countryName}" 
            pt:data-icon="flag flag-#{country.isoCode}" />   
    </c:forEach>             
</h:selectOneMenu>

See also:

• JSTL in JSF2 Facelets... makes sense?

来源：https://stackoverflow.com/questions/29671305/using-fselectitems-var-in-passtrough-attribute