I'm having the same epiphany as Paul did below. The cornucopia of flexibility(and gotchas) that LC's message path model provides using: 1) Standard issue calling of commands and functions. 2) Engine messages 3) Send (optionally in time) 4) Dispatch 5) Wait in time with/without messages 6) exit to top
And any others that I left out or don't know about can do things that I never could have imagined when I first found LC. Although I use all the above there's probably combinations I can't wrap my head around without more info. This would be a great as a dedicated chapter in a book and/or a Dr Mark W symposium followed by Q&A at the next RR Live. There seems to be a lot of app power/error prevention in the message path gold. For a newbie the LCs message path gold would be very attractive if it was only well documented and advertised. My 2 cents... Now back to changing some "wait with messages" to plain old waits to prevent users from clicking and getting my code into trouble now-and-again. Thanks to all on the list for this info!!! Ralph DiMola IT Director Evergreen Information Services rdim...@evergreeninfo.net -----Original Message----- From: use-livecode [mailto:use-livecode-boun...@lists.runrev.com] On Behalf Of Bob Sneidar via use-livecode Sent: Wednesday, August 03, 2022 12:15 PM To: How to use LiveCode Cc: Bob Sneidar Subject: Re: Dispatch One correction. If a value is returned by the handler that was called, the result will be that value. Bob S > On Aug 3, 2022, at 08:53 , Mark Wieder via use-livecode <use-livecode@lists.runrev.com> wrote: > > One, if I'm calling a handler in a different object that is outside the normal message path then I'll dispatch the handler to that object rather than using send. One caveat: note that the dispatch command returns a three-state value: "handled", "unhandled", and "passed". So on checking the return value I use "if it it not unhandled then...". The advantage is that there's no runtime error if the command isn't caught, at the slight disadvantage of having to check whether it was handled. On 7/30/2022 3:53 PM, Paul Dupuis via use-livecode wrote: > My understanding of 'wait 0 with messages' is that it will cause any > pending messages, that are not scheduled for a time later than the > current time, in the pendingMessages queue to be processed before > continuing. Messages later than the current time (when the statement > is executed) will not be processed (yet). > > Is this correct? > First, than you to those that have responded. The reason I got curious about 'wait 0 with messages' (or even just 'wait 0') is because of an epiphany I had just last week regarding a bug a customer reported in our software. The customer experienced and execution error and our software presents a custom dialog that allows them to email out support account some information, including the 'executionContexts' so we have some code debugging information. The problem as a 'can't find object' error. In reviewing the code, I could see no way that the error should have occurred. The code was using the ChartMaker library to create a graph. It all looked good per documentation and we could not reproduce the error in house. I then noticed a 'wait 0 with messages' prior to the line the error occurred on and noticed that the line that had the error used object references relative to the current stack (which the defaultStack was explicitly set to much prior). My epiphany was realizing - for the first time, despite LiveCodeing since HyperCard and having a Masters in Computer Science and my entire career being in the IT/software development space for over 40 years - that when the 'wait 0 with messages' is executed, if there was a pending USER click on another window, the defaultStack could change and then the relative object references would not be able to find their target objects. Perhaps I should have realized that a 'wait 0 with messages' COULD result in the defaultStack changing much sooner OR perhaps I should always fully qualify all object references (which I have been doing for quite a few years, but this was old code), but it is a 'gotcha' of using wait with messages I had never thought of. The Dictionary Entry (LC 9.6.8) does state "If the wait..with messages form is used, LiveCode continues normal processing during the wait. The current handler is frozen, but the user can start other handlers and perform other actions such as switching cards." and 'switching cards' does imply changing the context of relative object references even if the defaultStack does not change, so perhaps I should have realized, but didn't until just last week. Now I am very curious about exactly what wait 0 with messages does and also about what actions change the defaultStack. Does anyone know of an article or something someone has done to identify all the messages, commands, or functions that change (or potentially change) the defaultStack? _______________________________________________ use-livecode mailing list use-livecode@lists.runrev.com Please visit this url to subscribe, unsubscribe and manage your subscription preferences: http://lists.runrev.com/mailman/listinfo/use-livecode _______________________________________________ use-livecode mailing list use-livecode@lists.runrev.com Please visit this url to subscribe, unsubscribe and manage your subscription preferences: http://lists.runrev.com/mailman/listinfo/use-livecode
