Re: Emitting a signal leads to a failed assertion

[Ari Jolma <ari jolma tkk fi>]

muppet kirjoitti:
> On Nov 2, 2007, at 9:37 AM, Ari Jolma wrote:
>
> > GLib-GObject-CRITICAL **: g_object_notify: assertion `G_IS_OBJECT
> > (object)' failed
>
>   (gdb) run myscript --g-fatal-warnings otherargs...
>   (gdb) backtrace

sadly, the result is "no stack"

> However, you don't want to connect directly to the ScrolledWindow's 
> scrollbar, anyway.  The scrollbars are combination 
> view-and-controllers.  The horizontal and vertical adjustments are 
> what you actually want.  ScrolledWindow communicates with the scrollee 
> through the adjustments; you can programatically control the scrolling 
> with the adjustments; etc, etc, etc.

How do I then react to the user scrolling? I tried connecting at least 
scroll-event and scroll-child signals to the scrolled window, to the 
image, to the event box the image is in, but those don't fire the 
callback when the user simply scrolls with the mouse.

I realized that the heart of the problem is here. In the render method, 
I redraw the image and set the adjustments. For some reason I seem to be 
unable to do it simply:

$self->set_vadjustment(...)

instead I have to (can't make it work other way):

$self->{old_hadj} = $self->get_hscrollbar->get_adjustment; # prevents a 
warning
$self->get_hscrollbar->set_adjustment(...)

i.e. I have to store a reference to the adjustment, otherwise I get 
critical error as above. The critical error is 'GTK_IS_ADJUSTMENT 
failed', though

Also the critical error I was first reporting does not come from 
connecting to the value-changed signal per se, but from calling render 
after that. I.e., the process in the application is:

user scrolls the window
the value_changed method is called,
   which calls render and then sends an extent-changed signal
   the sub the application has connected to extent-changed is called,
       which also calls render
the value_changed method exits
the critical error happens

This is also poor design because the, potentially costly, render is 
called twice.

Ari