Re: Question about Callback

[Rudolfo Pinewood <rudolfo pinewood googlemail com>]

Hi,
thanks again for your help.
1) I did change my function to a static one
2) I updated my g_signal_connect_swapped to use G_CALLBACK(staticfunc) + 
param parent (which I use to get the other buttons)
3) I noticed that the pointers were in wrong order (parent was the first 
one instead of second) - changed to g_signal_connect instead and order 
is right.
I now can use my function as desired. I only have to integrate some 
other fields, but I think I'll get that ready with the knowledge I 
received here.

Many thanks!
Christoph Hartwig

James Scott Jr schrieb:
> Rudolfo,
>
> In your case where you have multiple buttons operating on the same
> logical data field, using a single callback function is very practical.
>
> The same can be said for a callback that performs a single logical
> function, all windows/object should attempt to reuse that callback if
> they need that functions.  
>
> Example; being a pair of callback I wrote that is called when a window
> is hidden or shown.  All my dialogs/windows that need that service reuse
> those single callbacks. To handle the fact that each window instance
> saves its visibility value in a different variable/address, I pass into
> the g_signal_connect(..., &b_visible) the address of that variable when
> creating each window.
>
> void cb_main_interface_show (GtkWidget * widget, gboolean *pb_visible)
> {
>   g_return_if_fail (pb_visible != NULL);
>   *pb_visible = TRUE;
> }
> void cb_main_interface_hide (GtkWidget * widget, gboolean *pb_visible)
> {
>   g_return_if_fail (pb_visible != NULL);
>   *pb_visible = FALSE;
> }
>
> To me this helps organize the code and makes it easier to maintain.  The
> cost of this reuse is fairly low, and the g_object_[set|get]_data()
> along with user-data cb_id flags, normally handles it well.  Of course
> all this reuse can be impacted by the to many global/static variables --
> which limits the re-entrancy or reuse  of any program.
>
> My two.
>
> James,
>
>
> On Tue, 2009-01-13 at 20:40 +0100, Rudolfo Pinewood wrote:
> > Hi,
> > thanks for your answer. I think I understand my code a bit better now...
> > I wonder whether it is "best practice" to use static functions for these 
> > callbacks - in my code it is actually a member function (because of 
> > having many different buttons whose states form a bitfield that is 
> > "compressed" to one int value. I did not find any example that does not 
> > use such static functions.
> >
> > Greetings,
> > Christoph Hartwig
> >
> > James Scott Jr schrieb:
> > > You can also use:
> > > - in the routine that creates the button, save a unique value.
> > >  g_object_set_data(G_OBJECT(button), "Unique-Key", &some-value)
> > >
> > > -in button callback routine, retrieve the unique value.
> > > some-value-pointer = g_object_get_data(G_OBJECT(button), "Unique-Key");
> > >
> > > This in addition to any pre-allocated memory structure you passed in the
> > > g_signal_connect(), or g_signal_connect_swapped().   The issue with
> > > reuse of button callbacks is always how to determine which button! I do
> > > two things;
> > > 1. pre-allocate a memory structure with the first value a fixed id of
> > > some sort (or related to the button's function).  example
> > >
> > > #def EXIT_BUTTON_FLAG 1
> > > .
> > > .
> > > .
> > > typedef struct _SomeButton {
> > >  gint cb_id;
> > >  ...
> > > } SomeButton, *PSomeButton;
> > > .
> > > .
> > > .
> > > PSomeButton memButton = NULL;
> > > .
> > > memButton = g_new0(SomeButton, 1);
> > > memButton->cb_id = EXIT_BUTTON_CBID;
> > > .
> > > g_signal_connect(G_OBJECT(button), "toggled", 
> > >           G_CALLBACK(fn_callback), memButton);
> > > .
> > > .
> > >
> > > 2. g_object_set_data() and g_object_get_data() as described earlier.
> > > checking the cb_id of the userdata from g_signal... and also getting
> > > this extra value helps your positively identify which button was
> > > pressed.  
> > >
> > > Either method will work, but sometimes both come in handy.
> > >
> > > Hope that helps.  Also, here is a link to source code that may help
> > > explain better.
> > > http://mysite.verizon.net/ressgdw8/sitebuildercontent/sitebuilderfiles/gtkstatusicon-starter-program-0.1.0.tar.bz2
> > >
> > > And don't forget to review 'gtk-demo', it has good examples.
> > >
> > > James,
> > >
> > >
> > > On Sun, 2009-01-11 at 12:42 +0100, Rudolfo Pinewood wrote:
> > > > Hi,
> > > > I have a question regarding Callback functions for Toggle buttons.
> > > >
> > > > I have several togglebuttons, that are all registered to call one
> > > > specific function (ApplyFlags). In this function I actually don't know
> > > > which button was activated.
> > > >
> > > > My attempt was giving each button/callback an additional parameter that
> > > > should be passed to my ApplyFlags function.
> > > >
> > > > However I was not able to do so - MemberCaller1 seems to fit (regarding
> > > > the "call one function with one parameter") but I did not manage to get
> > > > my parameter into that Callback in
> > > > g_signal_connect_swapped(G_OBJECT(button), "toggled", 
> > > > G_CALLBACK(callback.getThunk()), callback.getEnvironment()).
> > > >
> > > > How could this be done?
> > > > Thanks in advance
> > > > Christoph Hartwig
> > > > _______________________________________________
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> > > > gtk-app-devel-list gnome org
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