Tizen(Headed) Native API  6.5
theme_example_01.c
/*
 * gcc -o theme_example_01 theme_example_01.c `pkg-config --cflags --libs elementary`
 */
#include <Elementary.h>

char edj_path[PATH_MAX];

static void
btn_extension_click_cb(void *data EINA_UNUSED, Evas_Object *btn, void *ev EINA_UNUSED)
{
   const char *lbl = elm_object_text_get(btn);

   if (!strncmp(lbl, "Load", 4))
     {
        elm_theme_extension_add(NULL, edj_path);
        elm_object_text_set(btn, "Unload extension");
     }
   else if (!strncmp(lbl, "Unload", 6))
     {
        elm_theme_extension_del(NULL, edj_path);
        elm_object_text_set(btn, "Load extension");
     }
}

static void
btn_style_click_cb(void *data EINA_UNUSED, Evas_Object *btn, void *ev EINA_UNUSED)
{
   const char *styles[] = {
        "chucknorris",
        "default",
        "anchor"
   };
   static int sel_style = 0;

   sel_style = (sel_style + 1) % 3;
   elm_object_style_set(btn, styles[sel_style]);
}

EAPI_MAIN int
elm_main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   Evas_Object *win, *box, *btn;

   elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);

#ifdef PACKAGE_DATA_DIR
   elm_app_compile_data_dir_set(PACKAGE_DATA_DIR);
#endif
   if (ecore_file_exists("./theme_example.edj"))
     {
        strcpy(edj_path, "./theme_example.edj");
     }
   else
     {
        elm_app_info_set(elm_main, "elementary", "examples/theme_example.edj");
        snprintf(edj_path, sizeof(edj_path), "%s/examples/theme_example.edj",
                 elm_app_data_dir_get());
     }
   elm_theme_extension_add(NULL, edj_path);

   win = elm_win_util_standard_add("theme", "Theme example");
   elm_win_autodel_set(win, EINA_TRUE);

   box = elm_box_add(win);
   evas_object_size_hint_weight_set(box, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_win_resize_object_add(win, box);
   evas_object_show(box);

   btn = elm_button_add(win);
   elm_object_text_set(btn, "Unload extension");
   elm_box_pack_end(box, btn);
   evas_object_show(btn);
   evas_object_smart_callback_add(btn, "clicked", btn_extension_click_cb, NULL);

   btn = elm_button_add(win);
   elm_object_text_set(btn, "Switch style");
   elm_object_style_set(btn, "chucknorris");
   elm_box_pack_end(box, btn);
   evas_object_show(btn);
   evas_object_smart_callback_add(btn, "clicked", btn_style_click_cb, NULL);

   evas_object_resize(win, 300, 320);
   evas_object_show(win);

   elm_run();

   return 0;
}
ELM_MAIN()