OK, let's get to brass tacks. I have some derived values that are somewhat expensive to compute so I compute them once per request/response cycle and then they're in local instance variables (non-persisted).
The particular component in question (with the semi-expensive derived values) is used inside a loop and so may appear multiple times on a page. By default the first time I use the component I compute the value and then display from that computed value... The 2nd, 3rd, etc instance of those component on the page is actually the exact same Java instance and so the computed/derived ivar is still set. I've added a hack that records an original property value when the derived ivar is computed and if the original and current property values don't match I reset the derived ivar. It works, but it a total hack. The common way I'd imagine doing it is to listen to when the property (parameter) is set by Tapestry. But now that I've lain out the use case maybe some knows the "right" way to do this in Tapestry. Thanks, Ezra Epstein -----Original Message----- From: Jesse Kuhnert [mailto:[EMAIL PROTECTED] Sent: Monday, October 09, 2006 3:33 PM To: Tapestry users Subject: Re: How to observe property binding events There's also the org.apache.tapestry.event.ChangeObserver interface, though this is currently only used by the services in tapestry.persist to observe page property changes when they are being managed via a particular persistence strategy. (like session/client/etc..) ~Maybe~ it's an oversight, and maybe not..I guess that depends on what/why you are trying to do. You'll find that there is very little in the framework that wasn't put there for an actual need, so adding in support for things that no one has needed yet doesn't seem to fall in line with sound design. (imho of course..) If you can outline why you need this, and exactly what properties/conditions you'd want to observe we might be able to work something out...A general "anything" is harder to understand / design around. There is no such thing as a "parameter" property listener because parameters have no meaning in the context of something taking a parameter...There has to be a source for that parameter value (usually a page ) somewhere. On 10/9/06, Epstein, Ezra <[EMAIL PROTECTED]> wrote: > > Hi Jesse, > > Thanks for that reply. > > If I read it correctly, it sounds, simply, like the framework is > missing this feature. It's a pretty common thing to ask for listener > call-backs on framework events. ("Listener" here in the generic sense > rather than the way tapestry uses the term for direct-link targets.) > In short, this sounds like a design over-sight. It's common when > beans are bound to be able to receive a call-back -- Hibernate, for > example, offers this. So much of Tapestry seems "automagic" I'm > surprised that there's no way to register to be informed of the events as > they occur. > > If Howard's reading this perhaps he has a better perspective that he > may offer. > > Thanks, > > Ezra Epstein > Amazon.com - Developer Tools > 206-266-2259 > > > -----Original Message----- > From: Jesse Kuhnert [mailto:[EMAIL PROTECTED] > Sent: Friday, October 06, 2006 7:22 PM > To: Tapestry users > Subject: Re: How to observe property binding events > > Yes, but the usefulness of my answer largely depends on how > clever/efficient you are trying to be doing it. > > Now, there is IBinding. The one object to bind them all ;) > > If you work your way down the type hierarchy you'll find > AbstractBinding, which holds the method you care about most - > "setObject". This will be called by tapestry when managing all of the page > properties "automagically" > for you. > > Some of the magic happens in (for your exact case at least) > org.apache.tapestry.enhance.ParameterPropertyWorker. > > The other half of the work happens in each specific binding > implementation that will handle these set/get object calls..(Like ognl > bindings, etc..) > > I'm not sure where you are going with this but I guess you could use > the hivemind chain of command service sort of configuration (like I > did for org.apache.tapestry.services.ComponentRenderWorker ) to > generically call a single interface method for a hivemind > configuration point...Then you can contribute as many workers into the > chain you like if you decide that you have more than one use for it. > > Again...Not knowing what you are doing - and taking the exact > parameters given I'd probably extend and override the default > ParameterPropertyWorker (a hivemind service, so replacing it inline > with what Tapestry does already should be easy ) and just override > whatever section of code I needed to in that implementation to inject + call > my service reference. > > It may look a little complicated in there at first, but the whole > org.apache.tapestry.enhance package is filled with lots of different > enhancement works - and most of them inject a service into the object > they work on...So finding an easier to follow worker to reference > before modifying ParameterPropertyWorker might be easier. > > Hope that helps. > > On 10/6/06, Epstein, Ezra <[EMAIL PROTECTED]> wrote: > > > > I've got a component which accepts a parameter. I want to listen > > (receive a callback) when the parameter is set (bound). Does > > Tapestry provide such a facility? > > > > Thanks, > > > > Ezra Epstein > > > > > > > > > > > -- > Jesse Kuhnert > Tapestry/Dojo/(and a dash of TestNG), team member/developer > > Open source based consulting work centered around > dojo/tapestry/tacos/hivemind. http://blog.opencomponentry.com > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > -- Jesse Kuhnert Tapestry/Dojo/(and a dash of TestNG), team member/developer Open source based consulting work centered around dojo/tapestry/tacos/hivemind. http://blog.opencomponentry.com --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
