Details
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Bug
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Status: Resolved
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Major
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Resolution: Fixed
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4.1
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None
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Tapestery 4.1 Head, JBoss 4.0.4 GA, Windows XP
Description
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 