Migrating from libunique to GApplication or GtkApplication: GTK+ 3 Reference Manual

## Migrating from libunique to GApplication or 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.

Example 20. A unique application

Here is a simple application using libunique:

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    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:

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    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()`.