On 7/24/07, Christopher Giblin <[EMAIL PROTECTED]> wrote:
Hi, Update: In the meantime, I have implemented a TransitionDetector class which implements SCXMLListener and is registered with SCXMLExecutor. It is only slightly odd to program:transitionDetector.reset(); fsmExecutor.triggerEvent(ev); System.out.println("Transition : " + transitionDetector .isTransitionOccurred());
<snip/> Indeed. On the plus side, that can work off of the latest release.
That gives me a tactical solution for the time being. If I find that a query, as suggested in my original post, really is required, I will get back.
<snap/> I think in the longer term it will be possible to offer that feedback via the SCXMLExecutor#triggerEvent() method(s), which currently have a void return type (they could either return a boolean or the actual list of transitions followed -- which could be empty). This will require a major release (v1.0) if implemented, due to the change in method signature. If you want to make sure this stays on the radar, please file a ticket in JIRA [1]. -Rahul [1] http://jakarta.apache.org/commons/scxml/issue-tracking.html
Thanks, chris Christopher Giblin/Zurich/IBM wrote on 07/24/2007 12:00:36 PM: > Hi, > > Sorry for the delayed response. My remarks below. > > > Please prefix the email subject with [SCXML], since this mailing list > > is shared across all Commons components. I've added the prefix here. > > Thanks - I will be sure to in the future. > > > On 6/27/07, Christopher Giblin <[EMAIL PROTECTED]> wrote: > >> > >> Hi, > >> I am new to Commons SCXML. > >> Is it possible to determine whether an event would result in a transition, > >> without that transition occuring? Including evaluation of transition > >> conditions? > ><snip/> > > > > While the idea is interesting, we do not have such an "introspection mode". > > > > It wouldn't take too much effort to implement it, but: > > > a) Would probably increase the code smell factor a tad (if in > > introspection mode, then follow transition else just report back etc.) > > > b) Would require some API additions that might warrant a major release. > > > If you don't mind sharing in this public forum, why do you need such > > introspection? The SCXML specification doesn't talk about this. > > Understanding that interaction pattern may or may not help better > > answer the question, we will have to see :-) > > I am using SCXML to describe allowable states for an application. > Every event should result in a state transition. If no transition, > then I need to raise an error. Adding error states to the state > machine complicates it significantly. By comparison, simply > expressing all allowable transitions is more elegant. This requires > that the engine can be queried with an event to determine if it > would result in a transition. By default, SCXML ignores non- > applicable events, remaining in the current state. Remaining in the > same state is ok, but I need to know if an event transition occurred > or not, as said. One approach would be to register as a listener to > determine if a transition occurred. This results in an awkward > programming style, however, further compounded by my app having > perhaps hundreds of state machines. A program would be easier to > read if one could ask the engine if the event leads to a transition. > > I also considered clone the state machine, listening and then > triggering the event. Too much overhead, though. My code must also > be efficient. > > Or do you see a better way of dealing with this? > > Thanks, chris > > > > > -Rahul >
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