OBJ ID
LVGL provides an optional field in lv_obj_t
to store the object ID.
Object ID can be used in many cases, for example, to identify the object.
Or we can store a program backtrace to where the object is created.
Usage
Enable this feature by setting LV_USE_OBJ_ID
to 1 in lv_conf.h
.
Enable LV_OBJ_ID_AUTO_ASSIGN
to automatically assign an ID to object when it's created.
It's done by calling function lv_obj_assign_id()
from lv_obj_constructor()
.
You can either use your own ID generator by defining the function lv_obj_assign_id()
or you can utilize the built-in one.
To use the builtin ID generator, set LV_USE_OBJ_ID_BUILTIN
to 1.
You can directly access the ID by lv_obj_get_id(obj) or use API lv_obj_stringify_id(obj, buf, len) to get a string representation of the ID.
Use custom ID generator
Set LV_USE_OBJ_ID_BUILTIN
to 0 in lv_conf.h
.
Below APIs needed to be implemented and linked to lvgl.
void lv_obj_set_id(lv_obj_t * obj, void * id);
void lv_obj_assign_id(const lv_obj_class_t * class_p, lv_obj_t * obj);
void lv_obj_free_id(lv_obj_t * obj);
const char * lv_obj_stringify_id(lv_obj_t * obj, char * buf, uint32_t len);
int lv_obj_id_compare(void * id1, void * id2);
lv_obj_assign_id()
is called when an object is created. The object final class is passed from
parameter class_p
. Note it may be different than obj->class_p which is the class
currently being constructed.
lv_obj_free_id()
is called when object is deconstructed. Free any resource allocated in lv_obj_assign_id()
.
lv_obj_stringify_id()
converts id to a string representation. The string is stored in buf
.
Dump obj tree
Use API lv_obj_dump_tree(lv_obj_t * obj, int depth)
to dump the object tree.
It will walk through all children and print the object ID together with object address.
This is useful to debug UI crash. From log we can rebuilt UI the moment before crash. For example, if the obj is stored to a timer->user_data, but obj is deleted when timer expired. Timer callback will crash because of accessing wild pointer. From the dump log we can clearly see that the obj does not exist.
Find child by ID
Use API lv_obj_t * lv_obj_get_child_by_id(const lv_obj_t * obj, void * id)
to find a child by ID.
It will walk through all children and return the first child with the given ID.
.. Autogenerated