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Re: Prob with classes, widgets and event handler [message #32944 is a reply to message #32943]

Tue, 19 November 2002 09:38

savoie
Messages: 68
Registered: September 1996

Member

Sebastian Loebbert <sebaaihb@peach.zrz.TU-Berlin.DE> writes:

> Hi all,
>
> I try to write a class that contains some widgets. The event handler shall
> only call member functions of that class. To have access to the class, I
> try to put 'self' in the UVALUE of the base widget.
> When I 'GET' the UVALUE inside the event handler, self isn't a valid object.
> I attached a small example class which demonstrates the problem (when
> clicking on the 'dummy'-Button, self->DUMMY_FUN should be called, but the
> reference to self does not work. I tested that program on Win2000 and
> Linux with equal results).
>
> What am I doing wrong there?
> Is there a way to make the event handler a member function of the class?

Don't fear, this is a pretty common mistake. Your init function needs to
return 1 to be a valid object. [Didn't you take out a red pen and underline
that in your IDL Programming Techniques (Second Ed.) :) ]

> ;; init function
> FUNCTION OBJ_WIDGET::INIT
> self.DEBUG = 1
> IF (self.DEBUG GT 0) THEN print, "start: OBJ_WIDGET::INIT"
> res = self->CREATE_GUI()
> IF (self.DEBUG GT 0) THEN print, "done: OBJ_WIDGET::INIT"
return, 1
> END ;; of INIT

That will fix your problem.

But, I think you should take a look at a generic handler for object widgets.

the idea is that you don't have to store and retrieve the self object each
time, but you store a structure in the uvalue.

from a Fanning post...
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&a mp;safe=off&selm=MPG.17b8dc785d0409dc98994f%40news.frii. com
<fanning>

button = Widget_Button(bbase, Value='Quit', $
UVALUE={object:self, method:'Quit'})

All the event handler does is get the user value and dispatch the
event to this method of this object:

PRO EVENTHANDLER, event
Widget_Control, event.id, Get_UValue=cmd
Call_Method, cmd.object, cmd.method, event
END

</fanning>

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[Message index]

		Re: Prob with classes, widgets and event handler By: David Fanning on Wed, 20 November 2002 16:50
		Re: Prob with classes, widgets and event handler By: K. Bowman on Wed, 20 November 2002 12:07
		Re: Prob with classes, widgets and event handler By: David Fanning on Wed, 20 November 2002 08:22
		Re: Prob with classes, widgets and event handler By: James Kuyper on Wed, 20 November 2002 08:07
		Re: Prob with classes, widgets and event handler By: David Fanning on Wed, 20 November 2002 05:22
		Re: Prob with classes, widgets and event handler By: Sebastian Loebbert on Wed, 20 November 2002 02:30
		Re: Prob with classes, widgets and event handler By: David Fanning on Tue, 19 November 2002 09:52
		Re: Prob with classes, widgets and event handler By: savoie on Tue, 19 November 2002 09:38

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