[C][Tizen] Potrzebuje wyjaśnienie funkcji

typedef struct _item_data
{
    int index;
    char * list_name;
    Elm_Object_Item * item;
} item_data;

.
.
.

item_data * id;
.
.
.

id = calloc( sizeof( item_data ), 1 );
id->list_name = bt_menu_list[ index ];
id->index = index++;
id->item = elm_genlist_item_append( genlist, itc, id, NULL, ELM_GENLIST_ITEM_NONE, _evas_smart_cb, ad );

.
.
.
.
static void _evas_smart_cb( void * data, Evas_Object * obj, void * event_info )
{
    Elm_Object_Item * it = event_info;
    item_data * list = elm_object_item_data_get( it );
   
    dlog_print( DLOG_ERROR, LOG_TAG, "@@@ index = %d, list name = %s", list->index, list->list_name );
}