gtk2/docs/reference/gtk/migrating-GtkApplication.xml

<?xml version="1.0"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
]>
<chapter id="gtk-migrating-GtkApplication">

  <title>Migrating from libunique to GApplication or GtkApplication</title>

  <para>
    libunique offers 'unique application' support as well as ways to
    communicate with a running application instance. This is implemented
    in various ways, either using D-Bus, or socket-based communication.
  </para>

  <para>
    Starting with GLib 2.26, D-Bus support has been integrated into GIO
    in the form of GDBus, and #GApplication has been added to provide
    the same level of application support as libunique.
  </para>

  <example><title>A unique application</title>
  <para>Here is a simple application using libunique:
  <programlisting>
int
main (int argc, char *argv[])
{
  UniqueApp *app;
  GtkWidget *window;

  gtk_init (&amp;argc, &amp;argv);

  app = unique_app_new ("org.gtk.TestApplication", NULL);

  if (unique_app_is_running (app))
    {
      UniqueResponse response;

      response = unique_app_send_message (app, UNIQUE_ACTIVATE, NULL);
      g_object_unref (app);

      return response == UNIQUE_RESPONSE_OK ? 0 : 1;
    }

  window = create_my_window ();

  unique_app_watch_window (app, GTK_WINDOW (window));

  gtk_widget_show (window);

  gtk_main ();

  g_object_unref (app);

  return 0;
}
</programlisting>
The same application using GtkApplication:
<programlisting>
static void
activate (GtkApplication *app)
{
  GList *list;
  GtkWidget *window;

  list = gtk_application_get_windows (app);

  if (list)
    {
      gtk_window_present (GTK_WINDOW (list->data));
    }
  else
    {
      window = create_my_window ();
      gtk_window_set_application (GTK_WINDOW (window), app);
      gtk_widget_show (window);
    }
}

int
main (int argc, char *argv[])
{
  GtkApplication *app;
  gint status;

  app = gtk_application_new ("org.gtk.TestApplication", 0);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);

  status = g_application_run (app);

  g_object_unref (app);

  return status;
}
</programlisting>
</para>
</example>
  <section><title>Uniqueness</title>
    <para>
      Instead of creating a #UniqueApp with unique_app_new(), create
      a #GApplication with g_application_new() or a #GtkApplication
      with gtk_application_new(). The @name that was used with
      unique_app_new() is very likely usable as the @application_id for
      g_application_new() without any changes, and GtkApplication passes
      the <envar>DESKTOP_STARTUP_ID</envar> environment variable
      automatically.
    </para>
    <para>
      While libunique expects you to check for an already running instance
      yourself and activate it manually, GApplication handles all this on
      its own in g_application_run(). If you still need to find out if there
      is a running instance of your application, use
      g_application_get_is_remote() instead of unique_app_is_running().
    </para>
  </section>

  <section><title>Commands and Messages</title>
    <para>
      libunique lets you send messages with commands to a running
      instance using unique_app_send_message(). The commands can be either
      predefined or custom. Some of the predefined libunique commands have
      equivalents in GApplication. Instead of sending the %UNIQUE_ACTIVATE
      command, call g_application_activate(), instead of sending the
      %UNIQUE_OPEN command, call g_application_open(). The
      %UNIQUE_NEW and %UNIQUE_CLOSE and user-defined commands don't
      have direct replacement at this time.
    </para>

    <para>
      As a replacement for custom commands, GApplication implements the
      #GActionGroup interface and lets you add a group of actions with
      g_application_set_action_group(). The actions can then be invoked,
      either by using the D-Bus interface for #GAction directly, or by
      calling g_action_group_activate_action() from another instance of
      the GApplication. The #GApplication documentation contains an
      example for using GApplication with actions.
    </para>

    <para>
      For more complex needs, GApplication supports passing entire
      commandlines to the running instance.
    </para>
  </section>
</chapter>