Ddlist get_selected function always return the number of the option

when I use this function to get the ID index,
x = lv_ddlist_get_selected(my_List);
The system always return me the total number of the ddlist options.

I guess this is a bug.
When I try the get the selected str of the ddlist,
the function feed me the right str back.

Sorry, It’s my bad. LVGL feedback me the right data, I make a mistake, Sorry.