How to develop a System Indicator for Unity?

System Indicator Service

Well, it is really simpler then I expected. There is no specific API for it. Because it is just a GSimpleActionGroup & with corresponding GMenu's exported through DBus then Unity is told about their presence using declaration file with same name put in /usr/share/unity/indicators/. No need for any other library.

Here a very small C language example:

  1. Get a copy of tests/indicator-test-service.c from libindicator source

    apt-get source libindicator
    cp libindicator-*/tests/indicator-test-service.c .
    cp libindicator-*/tests/com.canonical.indicator.test* .
    
    • indicator-test-service.c no changes

      #include <gio/gio.h>
      
      typedef struct
      {
        GSimpleActionGroup *actions;
        GMenu *menu;
      
        guint actions_export_id;
        guint menu_export_id;
      } IndicatorTestService;
      
      static void
      bus_acquired (GDBusConnection *connection,
                    const gchar     *name,
                    gpointer         user_data)
      {
        IndicatorTestService *indicator = user_data;
        GError *error = NULL;
      
        indicator->actions_export_id = g_dbus_connection_export_action_group (connection,
                                                                              "/com/canonical/indicator/test",
                                                                              G_ACTION_GROUP (indicator->actions),
                                                                              &error);
        if (indicator->actions_export_id == 0)
          {
            g_warning ("cannot export action group: %s", error->message);
            g_error_free (error);
            return;
          }
      
        indicator->menu_export_id = g_dbus_connection_export_menu_model (connection,
                                                                         "/com/canonical/indicator/test/desktop",
                                                                         G_MENU_MODEL (indicator->menu),
                                                                         &error);
        if (indicator->menu_export_id == 0)
          {
            g_warning ("cannot export menu: %s", error->message);
            g_error_free (error);
            return;
          }
      }
      
      static void
      name_lost (GDBusConnection *connection,
                 const gchar     *name,
                 gpointer         user_data)
      {
        IndicatorTestService *indicator = user_data;
      
        if (indicator->actions_export_id)
          g_dbus_connection_unexport_action_group (connection, indicator->actions_export_id);
      
        if (indicator->menu_export_id)
          g_dbus_connection_unexport_menu_model (connection, indicator->menu_export_id);
      }
      
      static void
      activate_show (GSimpleAction *action,
                     GVariant      *parameter,
                     gpointer       user_data)
      {
        g_message ("showing");
      }
      
      int
      main (int argc, char **argv)
      {
        IndicatorTestService indicator = { 0 };
        GMenuItem *item;
        GMenu *submenu;
        GActionEntry entries[] = {
          { "_header", NULL, NULL, "{'label': <'Test'>,"
                                   " 'icon': <'indicator-test'>,"
                                   " 'accessible-desc': <'Test indicator'> }", NULL },
          { "show", activate_show, NULL, NULL, NULL }
        };
        GMainLoop *loop;
      
        indicator.actions = g_simple_action_group_new ();
        g_simple_action_group_add_entries (indicator.actions, entries, G_N_ELEMENTS (entries), NULL);
      
        submenu = g_menu_new ();
        g_menu_append (submenu, "Show", "indicator.show");
        item = g_menu_item_new (NULL, "indicator._header");
        g_menu_item_set_attribute (item, "x-canonical-type", "s", "com.canonical.indicator.root");
        g_menu_item_set_submenu (item, G_MENU_MODEL (submenu));
        indicator.menu = g_menu_new ();
        g_menu_append_item (indicator.menu, item);
      
        g_bus_own_name (G_BUS_TYPE_SESSION,
                        "com.canonical.indicator.test",
                        G_BUS_NAME_OWNER_FLAGS_NONE,
                        bus_acquired,
                        NULL,
                        name_lost,
                        &indicator,
                        NULL);
      
        loop = g_main_loop_new (NULL, FALSE);
        g_main_loop_run (loop);
      
        g_object_unref (submenu);
        g_object_unref (item);
        g_object_unref (indicator.actions);
        g_object_unref (indicator.menu);
        g_object_unref (loop);
      
        return 0;
      }
      
    • com.canonical.indicator.test modified to add lock & greeter mode

      [Indicator Service]
      Name=indicator-test
      ObjectPath=/com/canonical/indicator/test
      
      [desktop]
      ObjectPath=/com/canonical/indicator/test/desktop
      
      [desktop_greeter]
      ObjectPath=/com/canonical/indicator/test/desktop
      
      [desktop_lockscreen]
      ObjectPath=/com/canonical/indicator/test/desktop
      
    • com.canonical.indicator.test.service remove .in postfix from filename and change the executable path

      [D-BUS Service]
      Name=com.canonical.indicator.test
      Exec=/usr/lib/x86_64-linux-gnu/indicator-test/indicator-test-service
      
  2. Compile it

    gcc -o indicator-test-service indicator-test-service.c `pkg-config --cflags --libs gtk+-3.0`
    
  3. Manual Installation

    sudo su
    mkdir /usr/lib/x86_64-linux-gnu/indicator-test/
    cp indicator-test-service /usr/lib/x86_64-linux-gnu/indicator-test/
    cp com.canonical.indicator.test /usr/share/unity/indicators/
    cp com.canonical.indicator.test.service /usr/share/dbus-1/services/
    
  4. Configuration for Greeter, override the default indicators list

    • 90_unity-greeter.gschema.override

      [com.canonical.unity-greeter]
      indicators=['ug-accessibility', 'com.canonical.indicator.keyboard', 'com.canonical.indicator.session', 'com.canonical.indicator.datetime', 'com.canonical.indicator.power', 'com.canonical.indicator.sound', 'com.canonical.indicator.test', 'application']
      
    • Install

      cp 90_unity-greeter.gschema.override /usr/share/glib-2.0/schemas/
      glib-compile-schemas /usr/share/glib-2.0/schemas/
      
  5. Test

    sudo service lightdm restart
    

Notes

  • DBus service is troublesome, if you want user to be able to close application anytime. It is better to use autostart instead, like default indicators do.

  • I have uploaded ready files here:

    https://github.com/sneetsher/mysystemindicator_minimum

    and a modified copy here:

    https://github.com/sneetsher/mysystemindicator

    Where I have tried different menu for different mode. It could be installed and tested quickly.

  • This seems too simple and can be easily ported to any other language that have support for GIO Gnome lib (including DBus). As I'm looking for python, I may add it later.

References:

  • libindicator README: The indicator service file format

System Indicator Plugin

This is not full standalone indicator as the one above, it is just a share lib plugin, similar to libappmenu.so & libprintersmenu.so (application menu & printer indicator). It could be shown only in regular user session & greeter (Not on lock screen).

I couldn't make it work in my current machine, but I did before. Here the steps, may be I'm missing something.

  1. Using same source above of libindicator

    test/libdummy-indicator-*.c are examples (simple & visible the ones show up on the panel)

  2. Compile

    ./autogen.sh
    make
    
  3. Install

    sudo cp tests/.libs/libdummy-indicator-visible.so /usr/lib/indicators3/7/libdummy.so
    
  4. Configure to show in greeter screen

    • 90_unity-greeter.gschema.override use same name without lib prefix and .so extension.

      [com.canonical.unity-greeter]
      indicators=['ug-accessibility', 'com.canonical.indicator.keyboard', 'com.canonical.indicator.session', 'com.canonical.indicator.datetime', 'com.canonical.indicator.power', 'com.canonical.indicator.sound', 'application', 'dummy']
      
    • Install

      cp 90_unity-greeter.gschema.override /usr/share/glib-2.0/schemas/
      glib-compile-schemas /usr/share/glib-2.0/schemas/