Fix PSS algorithm to ensure c:if and ui:include src="#{...}" related use cases
will work without rely on
org.apache.myfaces.REFRESH_TRANSIENT_BUILD_ON_PSS_PRESERVE_STATE
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Key: MYFACES-3329
URL: https://issues.apache.org/jira/browse/MYFACES-3329
Project: MyFaces Core
Issue Type: Improvement
Components: JSR-314
Reporter: Leonardo Uribe
Assignee: Leonardo Uribe
There is a well known issue related to use c:if and ui:include src="#{...}". It
has been described in different ways for a long time. For example see:
MYFACES-3271 ui:include tag handler evaluates its bindings to soon during JSF
lifecycle
There is a lot of related issues but to keep things simple, PSS algorithm is
based on the following conditions:
1. Each time the view is build by first time or when it is restored, the same
initial state will be retrieved.
2. It is possible to calculate a delta state, based on that initial state.
In practice, there are some use cases that breaks that:
a. c:if tag
b. c:choose, c:when and c:otherwise
c. ui:include src="#{...}" (usually known as "dynamic include")
d. ui:decorate template="#{...}"
e. c:forEach
The reason is they change the component tree dynamically. For example a c:if
tag could be bound to a ValueExpression that in one moment could be true and
then false, so the "initial state" calculated by PSS algorithm through a
vdl.buildView() will be different each time, breaking condition 1.
It is true there exists the workaround with
org.apache.myfaces.REFRESH_TRANSIENT_BUILD_ON_PSS_PRESERVE_STATE, which mark
some parts of the tree to be restored fully, so it does not matter the initial
state, at the end just we restore such parts fully and everything works as
facelets 1.1.x. But even so, it is a workaround, and we need a better solution
to that.
In practice, points a., b., c. and d. are relevant. The case e. related to
c:forEach is not because the iterated data has
usually a life longer than the view (session, conversation or view scope), so
we can exclude this case.
The solution to this problem is store the result of the evaluated expressions
within the view. It is the only that will work
as good as org.apache.myfaces.REFRESH_TRANSIENT_BUILD_ON_PSS_PRESERVE_STATE.
To do that we need to generate an unique id per tag and make components and
tags inside them generate unique tags too but the
same ids should be generated each time the view is build no matter the
conditions. For example:
<h:outputText value="-A-"/>
<c:if test="#{condition}">
<h:outputText value="-B-"/>
</c:if>
<h:outputText value="-C-"/>
-C- should have the same id each time, no matter what happen inside c:if. Since
PSS algorithm uses clientIds to store the "delta" state of the components,
ensure that is CRITICAL, otherwise the state will get mixed or lost.
Additionally, we must restore that "facelet state" before the view is built to
use it when the initial state is derived.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
