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Re: IDLVM and retall [message #50010 is a reply to message #50009]

Thu, 07 September 2006 11:54

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Thu, 07 Sep 2006 07:52:09 -0600, David Fanning wrote:

> JD Smith writes:
>
>> [quoted text muted]
>
> I've been trying to follow this, but I confess, I am
> confused. Why is RETALL needed at all? I've never used
> anything but RETURN in event handler CATCH statements,
> and I have never had any problem running programs both
> from the command line and from the VM.

Sorry, my example doesn't really illustrate the original method that
well (just the problem I had with it in the VM).

Imagine you are in some deep level of the calling stack in a complex
widget program, and an error occurs. If you are running
interactively, you'd like to report the error to the user with a
dialog, and then after they dismiss it, continue running the
application. The only way to do this simply is to use RETALL, which
returns all the way to the active command line (a fact many have
discovered: when a widget app crashes, use RETALL and you're often
back in business). Widget events keep flowing, and everything is
happy. If you are running non-interactively, however, you'd like that
error to halt the processing with a call to MESSAGE. So you either
call RETALL, or MESSAGE, depending on whether you're interactive or
non-interactive. This is fine, *except* in the VM (which is of course
interactive by necessity). In the VM, RETALL returns all the way out
of the session, quitting IDL! Quite a surprise after acknowledging an
error.

> What usually screws people up is calling pop-up dialogs
> from their widget programs that rely on blocking behavior,
> rather than modal behavior. But that doesn't seem to be
> the issue here.

Nope, it's just my two-pronged "system" for handling errors doesn't
work in the VM. The larger context is my use of a "helper" class
which implements an Error method, so that at any point in my
object-widget app, I can simply say:

self->Error,'You screwed up'

and it will "do the right thing" with that error, either prompting the
user with a dialog, then returning all the way out to the active
command line and continue running (for interactive use), or issuing
the error message and halting (for scripted, non-interactive use).
The only workaround I could find was using a blocking initial call to
XManager, placed just after an explicit catch, in the VM only. Since
there's no command line, losing the active command line isn't really
important.

My code to dispatch the error then looks like:

if self->IsBlocking() then begin
;; Send a message to be caught by the established OBJREPORT catch
message,'OBJREPORT-ERROR',/NOPRINT
endif else if keyword_set(ro) then return else retall

with IsBlocking as:

;=========================================================== ==================
; isBlocking - Is the widget part of a blocking widget, or not?
;=========================================================== ==================
function ObjReport::IsBlocking
return,widget_info(self.or_widget,/XMANAGER_BLOCK)
end

where self.or_widget is the "reporting widget" atop which alerts will
be centered. Since the widget is blocking in the VM, MESSAGE will be
called, the top level CATCH will trip, and an argumentless call to
XManager will start the event loop up again.

JD

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[Message index]

		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:35
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:30
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:26
		Re: IDLVM and retall By: JD Smith on Fri, 08 September 2006 09:12
		Re: IDLVM and retall By: news.qwest.net on Fri, 08 September 2006 09:10
		Re: IDLVM and retall By: btt on Fri, 08 September 2006 09:02
		Re: IDLVM and retall By: news.qwest.net on Fri, 08 September 2006 08:42
		Re: IDLVM and retall By: David Fanning on Fri, 08 September 2006 08:28
		Re: IDLVM and retall By: btt on Fri, 08 September 2006 07:57
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 21:00
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 15:57
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 12:14
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 11:54
		Re: IDLVM and retall By: David Fanning on Thu, 07 September 2006 06:52
		Re: IDLVM and retall By: JD Smith on Thu, 07 September 2006 01:57
		Re: IDLVM and retall By: JD Smith on Wed, 06 September 2006 23:21
		Re: IDLVM and retall By: Foldy Lajos on Wed, 06 September 2006 12:30
		Re: IDLVM and retall By: JD Smith on Wed, 06 September 2006 11:53
		Re: IDLVM and retall By: Foldy Lajos on Tue, 05 September 2006 08:31
		Re: IDLVM and retall By: David Fanning on Fri, 08 September 2006 09:48

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