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:

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

Compile it

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

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/

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/

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.

Using same source above of libindicator

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

Install

sudo cp tests/.libs/libdummy-indicator-visible.so /usr/lib/indicators3/7/libdummy.so

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/

How to develop a System Indicator for Unity?

System Indicator Service

Notes

References:

System Indicator Plugin

Tags:

Python

C

Indicator

Application Development

Unity

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