How to use generated ids in EL (jsf, composite)? - jsf-2

Question

I want to have a composite that composes
<h:form id="f_imgA" >
<h:graphicImage id="imgA"
onclick="document.getElementById('#{k_imgA.clientId}').value=mods(event)"
value="images/img?r=#{Math.random()}">
<f:ajax event="click" listener="#{mBean.handleEvent}"
execute="#this k_imgA" render="#this"></f:ajax>
</h:graphicImage>
<h:inputHidden id="k_imgA" binding="#{k_imgA}" value="#{mBean.keyX}" />
</h:form>
when I write
<comps:cimg imgId="imgA" />
The original purpose of this code is to send the modifier-states (Ctrl, Shift, Alt) to the server.
I have
<composite:interface>
<composite:attribute name="imgId" />
</composite:interface>
<composite:implementation>
<h:form id="f_#{cc.attrs.imgId}">
<h:graphicImage id="#{cc.attrs.imgId}"
onclick="document.getElementById('#{k_${cc.attrs.imgId}.clientId}').value=mods(event)"
value="images/img?r=#{Math.random()}">
<f:ajax event="click" execute="#this k_#{cc.attrs.imgId}"
listener="#{mBean.handleEvent}" render="#this">
</f:ajax>
</h:graphicImage>
<h:inputHidden id="k_#{cc.attrs.imgId}"
binding="k_#{cc.attrs.imgId}" value="#{mBean.keyX}" />
</h:form>
</composite:implementation>
which, quite expected, does not work. The offending expression is
#{k_${cc.attrs.imgId}.clientId}
which is intended to return the clientId of the hiddenInput with id k_imgA . As far as I know, EL cannot handle nested expressions like the one above, but it was worth a try. So is there a simple, straightforward way to get the clientId of k_imgA? I don't want to use more javascript, if this can be avoided.
Edit:
don't get confused about #{Math.random()}, it works just because I have a bean called "Math".
The javascript function mods is given by
<h:outputScript target="body">function mods(event) {return ((event.ctrlKey)?1:0)+((event.shiftKey)?2:0)+((event.altKey)?4:0)} </h:outputScript>

Answer 1

You don't need to fiddle with all those _#{cc.attrs.imgId}. Just give the composite a fixed id. They are already naming containers themselves. JSF will then worry about the rest.
<composite:implementation>
<h:form id="f">
<h:graphicImage id="i" ... />
<h:inputHidden id="k" ... />
</h:form>
</composite:implementation>
Usage:
<comps:cimg id="imgA" />
Generated HTML:
<form id="imgA:f" ...>
<img id="imgA:f:i" ... />
<input id="imgA:f:k" ... />
</form>
As to the JS attempt, you'd best use element's own ID as base:
<h:graphicImage onclick="document.getElementById(id.substring(0,id.lastIndexOf(':')+1)+'k').value='...'" />
Or, easier, if the hidden element is guaranteed to be the direct sibling of the image element in the generated HTML DOM tree, then just grab it by Node#nextSibling:
<h:graphicImage onclick="nextSibling.value='...'" />
<h:inputHidden ... />
The binding will never work as in your attempted construct, and even then you'd best do it via a Map in request scope or a so-called backing component.
See also:
Accessing JSF nested composite component elements in JavaScript
Integrate JavaScript in JSF composite component, the clean way
Rerendering composite component by ajax