[jira] Assigned: (TAPESTRY-1023) Calling updateComponent in @EventListener method on a component that is prerendered results in null update

["Jesse Kuhnert (JIRA)" <ta...@jakarta.apache.org>]

     [ http://issues.apache.org/jira/browse/TAPESTRY-1023?page=all ]

Jesse Kuhnert reassigned TAPESTRY-1023:
---------------------------------------

    Assignee: Jesse Kuhnert

> Calling updateComponent in @EventListener method on a component that is prerendered results in null update
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: TAPESTRY-1023
>                 URL: http://issues.apache.org/jira/browse/TAPESTRY-1023
>             Project: Tapestry
>          Issue Type: Bug
>          Components: Framework
>    Affects Versions: 4.1
>         Environment: Tapestery 4.1 Head,  JBoss 4.0.4 GA,  Windows XP
>            Reporter: Ben Sommerville
>         Assigned To: Jesse Kuhnert
>
> I had a problem with @EventListener tonight but I'm not sure if this is a 
> bug or ignorance on my part. 
> (I am working with the latest 4.1 version from svn) 
>   
> First let me explain what I am trying to do.... 
> I have a form with several PropertySelection input fields on it.  What I 
> want to do is change the selectable options based on what has already been 
> selected.  
> e.g.  Say the form has two select fields A & B 
> A has options 1,2,3. 
> If the value of A is 1, then B should have options 11, 12, 13 
> If the value of A is 2, then B should have options 21, 22, 23 
> If the value of A is 3, then B should have options 31, 32, 33 
>   
> Now in the page template the fields are defined as follows 
>   
> <div class="field"> 
>     <label jwcid="@FieldLabel" field="component:A">Role</label> 
>     <input jwcid="A@PropertySelection" value="ognl:A" displayName="A" 
>            model="ognl:aModel"/> 
> </div> 
> <div class="field"> 
>     <label jwcid="@FieldLabel" field="component:B">B</label> 
>     <input jwcid="B@PropertySelection" value="ognl:B" displayName="B" 
>            model="ognl:bModel"/> 
> </div> 
> To update the options displayed by B I defined the following method 
> @EventListener(targets="A", events="onchange", submitForm ="form") 
> public void selectA(IRequestCycle cycle) { 
>    bModel = .... New model for b based on value of A .... 
>    cycle.getResponseBuilder().updateComponent("b"); 
> } 
>   
> What I was expecting to happen was that when the value of A was changed then 
> B would be rerendered with the new options based on A's value. 
> What actually happened was that as soon as I changed the value of A then B 
> was rendered with no options at all. 
> After a bit of debugging I eventually worked out that what was happening 
> was: 
> - A's value was changed & the event listener was invoked 
> - The model for B was updated correctly 
> - The FieldLabel that refered to B was rendered with a NullWriter 
> - this field label prerendered B (to get its id) with the NullWriter 
> - B was rendered with a real writer but didn't output anything because it 
> had been prerendered 
> - The page was updated an empty B element (cause the NullWriter discards 
> everything). 
> To work around this I gave the FieldLabel (for B) an explicit id and added 
> an updateComponent call for the this id.  When I did this the page behaved 
> as I was expecting. 
> Now my question: Is this behaviour correct? 
>                  Or have I approached the problem incorrectly? 
> It seems a bit unintuitive, I would prefer B to render properly when I asked 
> it to be updated, rather than having to update both it and the label. 
> However I'm not sure how to get my desired behaviour.  Maybe the 
> DojoAjaxResponseBuilder could check the form prerender map after each 
> component render and clear out any prerender's with null results.... 
> ...or maybe wiser heads can come up with a much more elegant solution :) 

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