foo.c

#include "screensaver-gdbus.h"

static void
active_changed_cb (FooDBusScreenSaver *proxy, gboolean active, gpointer user_data)
{
  g_print ("Signal: %s\n", active ? "Active" : "Inactive");
}

static void
get_active_cb (GObject *object, GAsyncResult *result, gpointer user_data)
{
  FooDBusScreenSaver *proxy = FOO_DBUS_SCREEN_SAVER (object);
  gboolean active;
  g_autoptr (GError) error = NULL;

  if (!foo_dbus_screen_saver_call_get_active_finish (proxy, &active, result, &error)) {
    g_error ("Failed to call active: %s", error->message);
  }

  g_print ("GetActive: %s\n", active ? "Active" : "Inactive");
}

static gboolean
timeout_cb (gpointer user_data)
{
  FooDBusScreenSaver *proxy = user_data;

  foo_dbus_screen_saver_call_get_active (proxy, NULL, get_active_cb, NULL);

  return TRUE;
}

static void
proxy_cb (GObject *object, GAsyncResult *result, gpointer user_data)
{
  FooDBusScreenSaver *proxy;
  g_autoptr (GError) error = NULL;
  
  proxy = foo_dbus_screen_saver_proxy_new_for_bus_finish (result, &error);

  if (!proxy) {
    g_error ("Failed to create proxy: %s", error->message);
  }

  g_signal_connect (proxy, "active-changed", G_CALLBACK (active_changed_cb), NULL);

  g_timeout_add_seconds_full (G_PRIORITY_LOW, 1, timeout_cb, proxy, g_object_unref);
}

int
main (int argc, char *argv[])
{
  g_autoptr (GMainLoop) mainloop = g_main_loop_new (NULL, TRUE);

  foo_dbus_screen_saver_proxy_new_for_bus (G_BUS_TYPE_SESSION, 0,
      "org.gnome.ScreenSaver", "/org/gnome/ScreenSaver", NULL, proxy_cb, NULL);

  g_main_loop_run (mainloop);
  return 0;
}

Makefile

foo: screensaver-gdbus.c foo.c
	$(CC) -Wall -Wextra -Wno-unused-parameter $(CFLAGS) -o $@ `pkg-config --cflags --libs glib-2.0 gio-2.0 gio-unix-2.0` $^

%-gdbus.c %-gdbus.h: %-dbus.xml
	gdbus-codegen --interface-prefix org.gnome. --generate-c-code $*-gdbus --c-namespace Foo_DBus $<

screensaver-dbus.xml:
	gdbus introspect -e -d org.gnome.ScreenSaver -o /org/gnome/ScreenSaver -x > $@

clean:
	rm -f foo screensaver-dbus.xml *-gdbus.?

.PHONY: clean