[jsr-314-open] minor feature enhancement for Facelets/VDL

Mon Apr 13 10:58:58 EDT 2009

Hey Dan -

I agree that this would be a useful feature.  I can easily imagine cases 
where template authors may want to selectively render some bit of 
content depending on whether a particular named template has been 
ui:define'd.

Actually, a similar case may come up with composite component facets, 
depending on how <composite:insertFacet> is implemented.  If inserted 
facets remain parented to the component component, then we should be 
able to use #{compositeComponent.facets.<facet name here>} to check for 
the presence of a particular facet.   However, if insertFacet relocates 
the facet component, seems like this would get trickier.

Andy

Dan Allen wrote On 4/8/2009 4:07 PM ET:
> I just thought of a feature I have often needed in Facelets that 
> perhaps we can weave into the VDL. It would be nice to know if a named 
> template has been defined inside the master template. Consider the 
> following example:
>
> page.xhtml
> <ui:composition template="/WEB-INF/template.xhtml" ...>
>     <ui:param name="title" value="VDL Template Page"/>
>     <ui:deﬁne name="content">
>          <h:outputText value="Hello World" />
>     </ui:deﬁne>
> </ui:composition>
>
> template.xhtml
> <html ...>
>     <h:head>
>         <title>#{not empty title ? title : 'My Site'}</title>
>     </h:head>
>     <body>
>         <div id="container">
>             <ui:insert name="content"/> <- how do I know if it has 
> been defined?
>         </div>
>     </body>
> </html>
>
> Since the <ui:param> creates a regular variable, I can check whether 
> it is empty or not. But I do not have a way to check if the named 
> template "content" has been defined. Of course, I can nest default 
> content within the <ui:insert>, which is used when the named template 
> is not defined, but there are cases when I simply need to know whether 
> or not it is defined. Could we come up with some way to check if it is 
> defined?
>
> -Dan
>
> -- 
> Dan Allen
> Senior Software Engineer, Red Hat | Author of Seam in Action
>
> http://mojavelinux.com
> http://mojavelinux.com/seaminaction
> http://in.relation.to/Bloggers/Dan
>
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