Handling component rendered state during postback

[Simon Kitching <sk...@ops.co.at>]

Hi,

A question on the user list reminded me of something I've been puzzled 
about for quite a while.

Does the JSF spec actually say that "rendered" EL expressions should be 
re-evaluated during postback? That's what MyFaces currently does, but it 
seems to me that the true/false state should really be part of the 
component's saved state and the restored value simply used during 
postback (and recalculated in render phase).

Does anyone know why in the current myfaces implementation each 
component recomputes its "rendered" state during postback by using its 
EL expression rather than using a value cached from the render phase?

Using a cached value would avoid some ugly problems with EL expressions 
being called before updateModel, as well as being a significant 
performance boost (rendered property tends to get queried several times 
during postback).

Regards, Simon

Re: Handling component rendered state during postback

[Gerhard Petracek <ge...@gmail.com>]

hello,

i agree with manfred.

regards,
gerhard



2008/10/13 Manfred Geiler <ma...@apache.org>

> My understanding of attributes with a value binding is, that the EL
> expressions must ALWAYS be evaluated dynamically and must never be
> cached.
> The same applies for the "rendered" attribute. There is (should be) no
> special handling IMHO.
> Regarding "ugly problems" and performance issues:
> My feeling is, that both can be avoided by having a well designed model.
> Please give us an example, Simon, if you cannot agree.
>
> --Manfred
>
>
> On Tue, Aug 5, 2008 at 4:27 PM, Simon Kitching <sk...@ops.co.at> wrote:
> > Hi,
> >
> > A question on the user list reminded me of something I've been puzzled
> about
> > for quite a while.
> >
> > Does the JSF spec actually say that "rendered" EL expressions should be
> > re-evaluated during postback? That's what MyFaces currently does, but it
> > seems to me that the true/false state should really be part of the
> > component's saved state and the restored value simply used during
> postback
> > (and recalculated in render phase).
> >
> > Does anyone know why in the current myfaces implementation each component
> > recomputes its "rendered" state during postback by using its EL
> expression
> > rather than using a value cached from the render phase?
> >
> > Using a cached value would avoid some ugly problems with EL expressions
> > being called before updateModel, as well as being a significant
> performance
> > boost (rendered property tends to get queried several times during
> > postback).
> >
> > Regards, Simon
> >
> >
>



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Re: Handling component rendered state during postback

[Manfred Geiler <ma...@apache.org>]

My understanding of attributes with a value binding is, that the EL
expressions must ALWAYS be evaluated dynamically and must never be
cached.
The same applies for the "rendered" attribute. There is (should be) no
special handling IMHO.
Regarding "ugly problems" and performance issues:
My feeling is, that both can be avoided by having a well designed model.
Please give us an example, Simon, if you cannot agree.

--Manfred


On Tue, Aug 5, 2008 at 4:27 PM, Simon Kitching <sk...@ops.co.at> wrote:
> Hi,
>
> A question on the user list reminded me of something I've been puzzled about
> for quite a while.
>
> Does the JSF spec actually say that "rendered" EL expressions should be
> re-evaluated during postback? That's what MyFaces currently does, but it
> seems to me that the true/false state should really be part of the
> component's saved state and the restored value simply used during postback
> (and recalculated in render phase).
>
> Does anyone know why in the current myfaces implementation each component
> recomputes its "rendered" state during postback by using its EL expression
> rather than using a value cached from the render phase?
>
> Using a cached value would avoid some ugly problems with EL expressions
> being called before updateModel, as well as being a significant performance
> boost (rendered property tends to get queried several times during
> postback).
>
> Regards, Simon
>
>