Re: callback_data in Gtk2::SimpleMenu [and Gtk2::ItemFactory (well, Gtk2.pm)]

["Ross McFarland" <rwmcfa1 neces com>]

Don Armstrong said:
> struct GtkItemFactoryEntry {
>
>   gchar *path;
>   gchar *accelerator;
>
>   GtkItemFactoryCallback callback;
>
> ....
> }
>
> void        gtk_item_factory_create_items   (GtkItemFactory *ifactory,
>                                              guint n_entries,
>                                              GtkItemFactoryEntry *entries,
>                                              gpointer callback_data);
>
> entries :     an array of GtkItemFactoryEntrys whose callback members must by of
> type GtkItemFactoryCallback1
>
> As you can see, create_items takes an array of GtkItemFactoryEntrys
> whose callback members are GtkItemFactoryCallback1.
>
> GtkItemFactoryCallback1 has it's own callback_data.
>
> void        (*GtkItemFactoryCallback1)      (gpointer callback_data,
>                                              guint callback_action,
>                                              GtkWidget *widget);

ah, now i see where you're getting hung up. callback is only a pointer to a
place in memory where the function resides. it's not a struct of
GtkItemFactoryCallback1 type. this is a pretty fundamental thing you have to
catch to work with glib/gtk+ in C. if you've not done much C development with
it then it's probably hard to guess just from looking at the doc. in fact the
doc is somewhat misleading until you learn how that stuff works.

in a C app things would look something like (this is just a made up case):

void
callback_func (gpointer callback_data,
               guint callback_action,
               GtkWidget *widget)
{
  /* do something really cool and interesting */
}

and the signal would be connected like:

g_object_signal_connect (item, "activate", &callback_func, callback_data);

callbac_func in thie case is of the GtkItemFactoryCallback1, but what's passed
there is only a pointer to the location in memory where that function is
located.

> Now, it's possible that the callback_data to create_items is totally
> separate from the callback_data in GtkItemFactoryCallback1. [If so,
> someone really needs to clean up the documentation in this area of the
> code, because it's not clear at all.]

as above, there's no object/struct etc. GtkItemFactoryCallback1, so there's
nothing in it. it's just a pointer to a function's location in memory and that
function has the call signature of a GtkItemFactoryCallback1.

> > it isn't the overhead of having the code to do it around, it's using
> > a hash ref instead of an array, which would both use up more memory
> > and time (tiny amounts, but still.)
>
> The hashref is created and goes away once it's out of scope and no
> longer referenced, so the memory useage and the time involved really
> isn't that big of a deal.

as i said, but not reason to change it now.

> There are places to make up time and memory useage, but if it causes
> the program to get locked into a particular design implementation, you
> have to weigh it carefully.

it hasn't. in my original email i showed how what you want could be done
without changing anything other than tacking on an extra array element that's
ignored by itemfactory and used in a special way by simplemenu.

> Regardless, as you're the person responsible for maintaining this
> slice of code, do it any way that works for you... it's merely a
> suggestion comming from someone who has seen the time it takes to keep
> a purely array based paramater system in sync with changing function
> calls.

in this case the array elements aren't defined by us, they're defined by the
structure itself which can't change in gtk+ b/c of API/ABI compatibility.

-rm