GTK basics : learning from sources - gtk

Question

I am new at programming Gtk gnome linux C application, and I am trying to learn from some source reagind and online gnome documentation but I can't do it because this is in my opinion very poor and bad. I have a problem understanding this following source: after creating a GObject of GApplication type, how can this main function call other parts of programs? (This is from gedit source) I learnt that GApplication doesn't include any pointer to some code.
/*
* gedit.c
* This file is part of gedit
*
* Copyright (C) 2005 - Paolo Maggi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "gedit-app.h"
#ifdef OS_OSX
#include "gedit-app-osx.h"
#else
#ifdef G_OS_WIN32
#include "gedit-app-win32.h"
#else
#include "gedit-app-x11.h"
#endif
#endif
#include <glib.h>
#include <locale.h>
#include <libintl.h>
#include "gedit-dirs.h"
#include "gedit-debug.h"
#ifdef G_OS_WIN32
#include <gmodule.h>
static GModule *libgedit_dll = NULL;
/* This code must live in gedit.exe, not in libgedit.dll, since the whole
* point is to find and load libgedit.dll.
*/
static gboolean
gedit_w32_load_private_dll (void)
{
gchar *dllpath;
gchar *prefix;
prefix = g_win32_get_package_installation_directory_of_module (NULL);
if (prefix != NULL)
{
/* Instead of g_module_open () it may be possible to do any of the
* following:
* A) Change PATH to "${dllpath}/lib/gedit;$PATH"
* B) Call SetDllDirectory ("${dllpath}/lib/gedit")
* C) Call AddDllDirectory ("${dllpath}/lib/gedit")
* But since we only have one library, and its name is known, may as well
* use gmodule.
*/
dllpath = g_build_filename (prefix, "lib", "gedit", "libgedit.dll", NULL);
g_free (prefix);
libgedit_dll = g_module_open (dllpath, 0);
if (libgedit_dll == NULL)
{
g_printerr ("Failed to load '%s': %s\n",
dllpath, g_module_error ());
}
g_free (dllpath);
}
if (libgedit_dll == NULL)
{
libgedit_dll = g_module_open ("libgedit.dll", 0);
if (libgedit_dll == NULL)
{
g_printerr ("Failed to load 'libgedit.dll': %s\n",
g_module_error ());
}
}
return (libgedit_dll != NULL);
}
static void
gedit_w32_unload_private_dll (void)
{
if (libgedit_dll)
{
g_module_close (libgedit_dll);
libgedit_dll = NULL;
}
}
#endif
int
main (int argc, char *argv[])
{
GType type;
GeditApp *app;
gint status;
const gchar *dir;
#ifdef OS_OSX
type = GEDIT_TYPE_APP_OSX;
#else
#ifdef G_OS_WIN32
if (!gedit_w32_load_private_dll ())
{
return 1;
}
type = GEDIT_TYPE_APP_WIN32;
#else
type = GEDIT_TYPE_APP_X11;
#endif
#endif
/* NOTE: we should not make any calls to the gedit api before the
* private library is loaded */
gedit_dirs_init ();
/* Setup locale/gettext */
setlocale (LC_ALL, "");
dir = gedit_dirs_get_gedit_locale_dir ();
bindtextdomain (GETTEXT_PACKAGE, dir);
bind_textdomain_codeset (GETTEXT_PACKAGE, "UTF-8");
textdomain (GETTEXT_PACKAGE);
app = g_object_new (type,
"application-id", "org.gnome.gedit",
"flags", G_APPLICATION_HANDLES_COMMAND_LINE | G_APPLICATION_HANDLES_OPEN,
NULL);
status = g_application_run (G_APPLICATION (app), argc, argv);
/* Break reference cycles caused by the PeasExtensionSet
* for GeditAppActivatable which holds a ref on the GeditApp
*/
g_object_run_dispose (G_OBJECT (app));
g_object_add_weak_pointer (G_OBJECT (app), (gpointer *) &app);
g_object_unref (app);
if (app != NULL)
{
gedit_debug_message (DEBUG_APP, "Leaking with %i refs",
G_OBJECT (app)->ref_count);
}
#ifdef G_OS_WIN32
gedit_w32_unload_private_dll ();
#endif
return status;
}
/* ex:set ts=8 noet: */