Re: g_signal_connect

[Paul Pogonyshev <pogonyshev gmx net>]

Tomaz Canabrava wrote:
> Little trouble here =)
>
> the g_signal_connect works like what?
> g_signal_connect(GTK_WIDGET(widget), signal("clicked"),
> G_CALLBACK(Function), (gpointer) "Data");
>
> but the callbacks functions have the GtkWidget *Widget as a 1st
> parameter, and...
> well, i simply don't get it. =)
>
> Does anyone cares to explain to this little noob the arts and secrets
> of the g_signal_connect?


void
some_callback (GtkWidget *widget, MyData *data)
{
  ...
}


void
alternative_callback (MyData *data, GtkWidget *widget)
{
  ...
}


  ...
  MyData *data = g_malloc (sizeof (MyData));
  data->foo = ...;
  data->bar = ...;

  /* Connect'em! */
  g_signal_connect (widget, "some-cute-signal-name",
                    G_CALLBACK (some_callback), data);
  g_signal_connect_swapped (widget, "some-cute-signal-name",
                            G_CALLBACK (alternative_callback), data);

If the signal has additional parameters, they always appear between
the instance argument and user data argument, no matter what their
order is (i.e. whether you use swapped/normal connection.)

You can drop arguments you don't use anyway from the functions if
you prefer.  Of course, you can only drop a tail of the argument list,
not e.g. remove the first argument and keep the second.

In the example above, `data' is leaked.  One common way to avoid it is
to use

  g_signal_connect_swapped (widget, "destroy",
                            G_CALLBACK (g_free), data);

However, be aware that certain widgets can be destroyed more than
once...

Paul