Use it. All of the time. If you're a long-time 4D devleloper like me, you may have started out not using ON ERR CALL much, if at all. I can't remember why I was scared of it, but I tended to avoid it. That all changed forever some versions back for me (6? 6.5?)
I think that it's 4D's job to give us errors, but it's our job to catch them. As 4D doesn't have anything else, ON ERR CALL is the tool to use. If you're one of the people that doesn't use it (there must be some), it might help to understand that ON ERR CALL serves a couple of purposes: * Catch errors that are outside of our control and that we can deal with. For example, if you deal with the file system, you may get a file locked error. That's not a bug in our code, it's information about the current state of play in the world. So, ON ERR CALL is functioning as a helpful probe. * Catch errors that shouldn't happen. Like, you know, those darn 4D bugs that we write into our code ;-) Very helpful! Record them, dump details to disk/record and you give yourself a huge head start on solving the problem. If you haven't worked with ON ERR CALL in some time, you'll also be happy to know that there is a lot more information available than there used to be. In the past, there was the Error system variable. Now there's a lot more: Error method The name of the method that caused the error. Error line The line of code that caused the error. Error formula The text of the formula where the error occurred. (Really? When did this show up? I never noticed it before.) Additionally, the GET LAST ERROR STACK provides programmatic access to the error details you may have seen in the new(ish) 4D error dialog. Docs for 16.1: ON ERR CALL http://doc.4d.com/4Dv16/4D/16.1/ON-ERR-CALL.301-3374749.en.html GET LAST ERROR STACK http://doc.4d.com/4Dv16/4D/16.1/GET-LAST-ERROR-STACK.301-3374753.en.html System Variables http://doc.4d.com/4Dv16/4D/16.1/System-Variables.300-3374917.en.html#205035 If you haven't been using ON ERR CALL everywhere, there are some details to sort out. Mainly, what handler applies where on the 4D Server machine. I don't remember them off the top of my head but I do remember that it mattered if you are running compiled or not. I think that triggers share one error handler compiled but need a custom one installed for each trigger in interpreted? Perhaps someone else can post a summary of the current situation. The normal way it works (in almost all cases) is that there is one error handler per process. If there's no custom handler, you fall back on 4D's. If you install a handler, the previous one is cleared. I use a custom stack to track handlers in case I want to install a more specific one and then restore the previous one...but everyone develops there own style. It would be great if some other folks could comment on how they use ON ERR CALL in support of our friends that may not be using it to it's fullest. Anything along these lines is helpful to know: * Gotchas * Details on what to install where * Places that they don't work * What to do with errors * How you handle handlers (like my stack) * Gripes, suggestions, tips ********************************************************************** 4D Internet Users Group (4D iNUG) FAQ: http://lists.4d.com/faqnug.html Archive: http://lists.4d.com/archives.html Options: http://lists.4d.com/mailman/options/4d_tech Unsub: mailto:[email protected] **********************************************************************
