Dear Rahul, dear all,
I'd like to use global targetless transitions to handle events occurring
asynchronously without leaving the context of the current state. Thus common
business logic (executable content within the transition) is inherited or
overwritten locally by any substate. It allows for chaining via
send/transition
pipes for more complex, conditional behaviour. Since the transitions are
defined
in a different, global scope, data are passed either via global datamodels or
via
the implicit event payload. My use case is a state machine, where some events
should
by handled without the "side effect" of triggerring a state transition (the
main
execution path) asynchronously as they arrive from multiple clients
interacting
with the SCXML session (e.g. error handling, views on datamodel and current
status ...)
I encounter problems when trying to send and evaluate the event payload.
There seems to be
no _eventdata available within the transition handling the event "view",
although the
parameter "text" is obviously declared. This code is run with Commons SCXML
v0.9:
<scxml initialstate="main" version="1.0"
xmlns="http://www.w3.org/2005/07/scxml";>
<state id="main">
<initial>
<transition target="sub1" />
</initial>
<datamodel>
<data id="text" expr="'TEXT MESSAGE'"></data>
</datamodel>
<!-- event handler processing the event payload without performing a
transition -->
<transition event="view">
<log expr="'viewing text message: '"/>
<log expr="_eventdata"/>
<log expr="text"/>
<!-- chained handler -->
<if cond="_eventdata == null"><send event="'view_specific'"/></if>
</transition>
<transition event="view_specific">
<log expr="'no _eventdata found'"/>
</transition>
<state id="sub1" final="true">
<onentry>
<log expr="'sending text message: '+text"/>
<send event="'view'" namelist="text" />
</onentry>
</state>
</state>
</scxml>
It produces the following log statements:
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.env.SimpleSCXMLListener
onEntry
INFO: /main
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.model.Log execute
INFO: null: sending text message: TEXT MESSAGE
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.env.SimpleSCXMLListener
onEntry
INFO: /main/sub1
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.model.Log execute
INFO: null: viewing text message:
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.model.Log execute
INFO: null: null
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.model.Log execute
INFO: null: TEXT MESSAGE
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.env.SimpleSCXMLListener
onTransition
INFO: transition (event = view, cond = null, from = /main, to = /main)
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.model.Log execute
INFO: null: no _eventdata found
Dec 29, 2008 10:42:12 AM org.apache.commons.scxml.env.SimpleSCXMLListener
onTransition
INFO: transition (event = view_specific, cond = null, from = /main, to =
/main)
It's probably my fault using a wrong syntax. Could you please suggest a way
how to:
1) access the simple string content of _eventdata ?
2) access XML _eventdata via XPath ?
3) send a subtree of an XML data model along with an event ?
To handle 3) and transition chaines passing arbitrary data chunks via named
parameters the <send> element, like <invoke>, could use <param> child elements
to explicitly declare its data interface decoupled from the datamodel ?
Is there any reason <event>, unlkike <send>, does not support any sort of
parametrization
in the current WD and such the event name itself has to encode the respective
parameter-value
information ?
Many thanks for your support
Jaro
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