evaluate_template() and object events

[G Gabriel]

Something puzzled me for the last few minutes, figured it out and thought I post it for others for reference value.
I have a script that runs in the OnChange event of an object on a form.
On testing the script, it seemed to run twice for no logical reason.
When placing the same script in the OnDepart event, it runs once!

There is so many complicating factors, for instance the script takes part of the name of the object and runs based on that part and when departing from one object to another where that part of the name is identical in both objects, made it rather more difficult to decipher what was happening thinking maybe it did so because of the similarity in that part of the name.

But that wasn't it.
It dawned on me that one line of of the script changes the value of the object itself under certain conditions. That change is done through evaluate_template() that takes the object's name and changes its value.
I began to wonder, if when evaluate_template() executes and changes the value of the object you are in and if that object has an OnChange event, I began to wonder if that triggers the OnChange event, yet again?
Upon further testing, I found out that it does, hence the script runs twice When placed in the OnChange, but only once when placed in the OnDepart.
Just keep that in mind for future reference to save yourself few minutes (or hours) of pondering and puzzling.

[G Gabriel]

Re: evaluate_template() and object events

Word of caution:
This (evaluate_template()) is a demonic function. Careful whenever you use it on any object containing events. Its like playing with hot wire. You better know what you are doing.

[martinwcole]

Re: evaluate_template() and object events

Gabe - a number of years ago, version 4.5 as I recall, developers found that certain events would fire more than once. Selwyn came up with a solution. (This may be of help, although it does not address the evaluate_template issue.)

define a global variable called busy
at the onchange event put this:

dim global busy as L
if busy
     end
end if 
busy=.t.
'event code
busy=.f.

[G Gabriel]

Re: evaluate_template() and object events

Thanks martin. I got around this by disabling the event then re-enabling it. It just puzzled me for a little while then I figured it out and thought I'd share it with others so they do not think they were imagining things or that their computer was invaded by aliens. But again, this could be rather dangerous if you are not aware of it as you might inadvertently run a script when you didn't mean to.

[martinwcole]

Re: evaluate_template() and object events

exactomundo!

PS: this can also occur at other events, especially the "can" events - canarrive, etc.