Migrating from libunique to GtkApplication

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.

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.

Here is a simple application using libunique:

int
main (int argc, char *argv[])
{
  UniqueApp *app;
  GtkWidget *window;

  gtk_init (&argc, &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;
}

The same application using GtkApplication:

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 (G_APPLICATION (app), argc, argv);

  g_object_unref (app);

  return status;
}

Uniqueness

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 DESKTOP_STARTUP_ID environment variable automatically.

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().