Theme - Using overlays

Overlays are like extensions in that you tell Elementary that some other theme contains the styles you need for your program. The difference is that they will be look in first, so they can override the default style of any widget.

There's not much to say about them that hasn't been said in our previous example about extensions, so going quickly through the code we have a function to load or unload the theme, which will be called when we click any button.

#include <Elementary.h>
static void
_btn_clicked_cb(void *data EINA_UNUSED, Evas_Object *obj EINA_UNUSED, void *ev EINA_UNUSED)
{
static int loaded = 1;
if (loaded)
elm_theme_overlay_del(NULL, edj_path);
else
elm_theme_overlay_add(NULL, edj_path);
loaded = 1 - loaded;
}
EINA_UNUSED
#define EINA_UNUSED
Used to indicate that a function parameter is purposely unused.
Definition eina_types.h:339
elm_theme_overlay_del
void elm_theme_overlay_del(Elm_Theme *th, const char *item)
Delete a theme overlay from the list of overlays.
Definition elm_theme.c:718
elm_theme_overlay_add
void elm_theme_overlay_add(Elm_Theme *th, const char *item)
Prepends a theme overlay to the list of overlays.
Definition elm_theme.c:710
Evas_Object
Efl_Canvas_Object Evas_Object
An Evas Object handle.
Definition Evas_Common.h:185

And the main function, creating the window and adding some buttons to it. We load our theme as an overlay and nothing else. Notice there's no style set for any button there, which means they should be using the default that we override.

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_overlay_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, "Button 1");
elm_box_pack_end(box, btn);
evas_object_show(btn);
evas_object_smart_callback_add(btn, "clicked", _btn_clicked_cb, NULL);
btn = elm_button_add(win);
elm_object_text_set(btn, "Button 2");
elm_box_pack_end(box, btn);
evas_object_show(btn);
evas_object_smart_callback_add(btn, "clicked", _btn_clicked_cb, NULL);
btn = elm_button_add(win);
elm_object_text_set(btn, "Button 3");
elm_box_pack_end(box, btn);
evas_object_show(btn);
evas_object_smart_callback_add(btn, "clicked", _btn_clicked_cb, NULL);
btn = elm_button_add(win);
elm_object_text_set(btn, "Button 4");
elm_box_pack_end(box, btn);
evas_object_show(btn);
evas_object_smart_callback_add(btn, "clicked", _btn_clicked_cb, NULL);
evas_object_resize(win, 300, 320);
evas_object_show(win);
elm_run();
return 0;
}
ELM_MAIN()
EVAS_HINT_EXPAND
#define EVAS_HINT_EXPAND
Use with evas_object_size_hint_weight_set(), evas_object_size_hint_weight_get(), evas_object_size_hin...
Definition Evas_Common.h:297
ecore_file_exists
Eina_Bool ecore_file_exists(const char *file)
Checks if the given file exists.
Definition ecore_file.c:165
EINA_TRUE
#define EINA_TRUE
boolean value TRUE (numerical value 1)
Definition eina_types.h:539
elm_app_info_set
void elm_app_info_set(void *mainfunc, const char *dom, const char *checkfile)
Re-locate the application somewhere else after compilation, if the developer wishes for easier distri...
Definition elm_main.c:496
elm_app_compile_data_dir_set
void elm_app_compile_data_dir_set(const char *dir)
Provide information on the fallback application's data directory, on scenarios where they get overrid...
Definition elm_main.c:528
elm_app_data_dir_get
const char * elm_app_data_dir_get(void)
Get the application's run time data prefix directory, as set by elm_app_info_set() and the way (envir...
Definition elm_main.c:586
elm_box_add
Evas_Object * elm_box_add(Evas_Object *parent)
Add a new box to the parent.
Definition elm_box.c:363
elm_box_pack_end
void elm_box_pack_end(Elm_Box *obj, Efl_Canvas_Object *subobj)
Add an object at the end of the pack list.
Definition elm_box_eo.legacy.c:57
elm_button_add
Evas_Object * elm_button_add(Evas_Object *parent)
Add a new button to the parent's canvas.
Definition efl_ui_button.c:459
ELM_MAIN
#define ELM_MAIN()
macro to be used after the elm_main() function
Definition elm_general.h:556
elm_policy_set
Eina_Bool elm_policy_set(unsigned int policy, int value)
Set a new policy's value (for a given policy group/identifier).
Definition elm_main.c:1380
elm_run
void elm_run(void)
Run Elementary's main loop.
Definition elm_main.c:1357
ELM_POLICY_QUIT_LAST_WINDOW_CLOSED
@ ELM_POLICY_QUIT_LAST_WINDOW_CLOSED
quit when the application's last window is closed
Definition elm_general.h:248
ELM_POLICY_QUIT
@ ELM_POLICY_QUIT
under which circumstances the application should quit automatically.
Definition elm_general.h:227
elm_win_util_standard_add
Evas_Object * elm_win_util_standard_add(const char *name, const char *title)
Adds a window object with standard setup.
Definition efl_ui_win.c:9587
elm_win_resize_object_add
void elm_win_resize_object_add(Eo *obj, Evas_Object *subobj)
Add subobj as a resize object of window obj.
Definition efl_ui_win.c:9002
elm_win_autodel_set
void elm_win_autodel_set(Eo *obj, Eina_Bool autodel)
Set the window's autodel state.
Definition efl_ui_win.c:6199
evas_object_show
EVAS_API void evas_object_show(Evas_Object *eo_obj)
Makes the given Evas object visible.
Definition evas_object_main.c:1814
evas_object_size_hint_weight_set
EVAS_API void evas_object_size_hint_weight_set(Evas_Object *obj, double x, double y)
Sets the hints for an object's weight.
Definition evas_object_main.c:2638
evas_object_resize
EVAS_API void evas_object_resize(Evas_Object *obj, Evas_Coord w, Evas_Coord h)
Changes the size of the given Evas object.
Definition evas_object_main.c:1236
evas_object_smart_callback_add
EVAS_API void evas_object_smart_callback_add(Evas_Object *eo_obj, const char *event, Evas_Smart_Cb func, const void *data)
Add (register) a callback function to the smart event specified by event on the smart object obj.
Definition evas_object_smart.c:1040

That's pretty much it. The full code is here and the definition of the theme is the same as before, and can be found in here.