Re: Wrapping GtkPlacesSidebar

[Juan Rafael García Blanco <juanrgar gmail com>]

On Mon, 2013-08-26 at 19:50 +0100, Chris Vine wrote:
> On Mon, 26 Aug 2013 09:00:34 +0200
> Kjell Ahlstedt <kjell ahlstedt bredband net> wrote:
> > 2013-08-25 12:19, Juan Rafael Garcia Blanco skrev:
> > > Hello,
> > >
> > > I'm fairly new to developing inside gtkmm. I'm trying to wrap 
> > > GtkPlacesSidebar. I managed to get a first version 
> > > (https://bugzilla.gnome.org/show_bug.cgi?id=705642) and now I'm 
> > > writing a simple example to test it.
> > >
> > > In that example program I attach a handler to the open-location 
> > > signal. That signal, when emitted, provides a Gio::File object in
> > > the form of Glib::Object; when it is emitted I get this message:
> > >
> > > glibmm-WARNING **: Failed to wrap object of type 'GLocalFile'.
> > > Hint: this error is commonly caused by failing to call a library
> > > init() function.
> > >
> > > GtkPlacesSidebar docs state that the signature for that signal
> > > handler should be:
> > >
> > > void user_function (GtkPlacesSidebar *sidebar,
> > >  GObject *location,
> > >  ...)
> > >
> > > where location is a GFile.
> > >
> > > I've added Gio::init() at the beginning of my main.cc, but the
> > > problem remains. I would like to learn how this can be done, and
> > > why it is not working.
> > >
> > > Thank you very much in advance.
> > >
> > > Regards,
> > > Juan.
> > gtk_init() must be called in a gtk+ program, and thus also in a gtkmm 
> > program. gtk_init() is called by
> >    Gtk::Application::create(int& argc, char**& argv, const 
> > Glib::ustring& application_id, Gio::ApplicationFlags flags)
> > but it's not called by
> >    Gtk::Application::create(const Glib::ustring& application_id, 
> > Gio::ApplicationFlags flags)
> >
> > Don't know if this is bug, or done deliberately. My guess is that
> > both Gtk::Application::create() shall call gtk_init().
> > Don't know if a missing call to gtk_init() is the reason for your 
> > warning message.
>
> g_application_run() is not subclassed in GtkApplication to call
> gtk_init(), and it doesn't need to be because GtkApplication itself
> initializes GTK+ when the object is constructed.  When using
> GtkApplication you can call gtk_init(), but you do not have to.  The
> main point is that g_application_run() does not strip out command line
> arguments which are GTK+ specific, such as --display and the like.
> That is the only reason, in a GTK+ program, to call gtk_init() with
> GtkApplication.  (I think the suggestion is that you should not do so,
> but should use environmental variables or the GOptionGroup/GOptionEntry
> interface.)
>
> Given the different approach to library initialization taken by gtkmm,
> this no doubt caused a problem.  The decision seems to have been taken
> to pass the program arguments to gtk_init() when they are passed to
> Gtk::Application::create(), but not to call gtk_init() otherwise.  This
> should work OK.  The problem may lie elsewhere: perhaps there is
> something wrong about the use of (or wrapping of) GApplication's 'open'
> signal.
>
> Chris

I think the problem is not related to missing ::init() funtions. I think
the problem has something to do with the fact that the handler takes a
GObject instead of a GFile. I think I'm missing some _CONVERSION macro.
As I said the open_location signal handler takes a GFile argument as a
GObject. I'm wrapping it with this line:

_WRAP_SIGNAL(void open_location(const Glib::RefPtr<Glib::Object>&
location, PlacesOpenFlags open_flags=Gtk::PLACES_OPEN_NORMAL),
"open_location");

I took a look at how Gtk::Entry has wrapped the populate_popup signal,
which also takes a GtkWidget argument that actually is a GMenu. But it
gives me little information since the wrapped signal handler does not
use RefPtr<>.

Thank you in advance.