Re: strangeness of g_signal_connect

[Annamalai Gurusami <annamalai gurusami EMAIL masconit com>]

Colossus <colossus 3000 it> writes:

> In my app I have the following:
>
> g_signal_connect ((gpointer) AddFile_button, "clicked",
>                      G_CALLBACK (on_add_files_activate),
>                      "dummy");

I normally write the above call like this:

g_signal_connect( G_OBJECT(AddFile_button), "clicked",
                  G_CALLBACK(on_add_files_activate), "dummy");

Are both correct?  Which is the preferred way to do it?

> I have noticed that if the function "on_add_files_activate" is
> declared with only one parameter, gpointer data , I never receive
> the word dummy. Instead if the same function is declared with two
> parameters:
>
> void on_add_files_activate ( GtkWidget *useless , gpointer data);
> I can successfull print the value "dummy" pointed by data.
>
> Could gtk developers explain this strange behaviour please ?

The actual parameters of the callback function is determined by the
event and the widget handling the event.  Here you are handling the
"clicked" event for a GtkButton.  And for this event, the prototype of
the callback handler is

void user_function(GtkButton *button,  gpointer user_data);

http://developer.gnome.org/doc/API/2.0/gtk/GtkButton.html#GtkButton-clicked

You can use it or not, but you cannot change their order or add more
arguments.  Maybe others can add more information on this.

Rgds,
anna

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