action param is null

[jmchiaradia]

Hello, I'm new in SEAM and I'm having a problem with an action parameter.

I have a datagrid iterating over a files collection of my backing bean. For each file of my datagrid, I want a commandButton that calls 'download(file)' action.
The problem is that file is null when the action is called.

Here is the code:

<rich:dataGrid columns="1" value="#{fileUploadBean.uploadedFiles}"
     var="_file" rowKeyVar="fileId">
     <rich:panel bodyClass="rich-laguna-panel-no-header">
          <h:panelGrid columns="2">
               <s:button action="#{fileDownloadBean.downloadFile(_file)}" value="Download"/>
               <h:outputText value="Nombre:" />
          </h:panelGrid>
     </rich:panel>
</rich:dataGrid>

Could you help me?

Regards,
Chiara

[jmchiaradia]

I found another thread that explain this problem:

http://seamframework.org/Community/UsingSeamELToPassParametersToActionMethodsDoesntAlwaysWork

[jmchiaradia]

In more detail:

The problem was in using s:commandButton.

From JBOSS El reference:

Use inside iterative components - Components like c:forEach and ui:repeat iterate over a List or array, exposing each item in the list to nested components. This works great if you are selecting a row using a h:commandButton or h:commandLink

However if you want to use s:link or s:button you must expose the items as a DataModel, and use a dataTable (or equivalent from a component set like rich:dataTable ). Neither s:link or s:button submit the form (and therefore produce a bookmarkable link) so a magic parameter is needed to recreate the item when the action method is called. This magic parameter can only be added when a data table backed by a DataModel is used.

Then, I replace s:commandButton with h:commandButton and it works just find.

<rich:dataGrid columns="1" value="#{fileUploadBean.uploadedFiles}"
     var="_file" rowKeyVar="fileId">
     <rich:panel bodyClass="rich-laguna-panel-no-header">
          <h:panelGrid columns="2">
               <h:commandButton action="#{fileDownloadBean.downloadFile(_file)}" value="Download" propagation="join"/>
               <h:panelGrid columns="2">
                    <h:outputText value="Nombre:" />
                    <rich:inplaceInput id="nameField" value="#{_file.name}" required="true" immediate="true" >
                         <a:support event="onchange"  
                              bypassUpdates="false" reRender="nameField, nameFieldOut"/>
                    </rich:inplaceInput>
               </h:panelGrid>
          </h:panelGrid>
     </rich:panel>
</rich:dataGrid>