lv_obj_add_event_cb() function
Add an event handler function for an object. Used by the user to react on event which happens with the object. An object can have multiple event handler. They will be called in the same order as they were added.
Arguments
event_cb
the new event function
filter
an event code (e.g. `LV_EVENT_CLICKED`) on which the event should be called. `LV_EVENT_ALL` can be used to receive all the events.
user_data
custom data will be available in `event_cb`
Return value
handler to the event. It can be used in `lv_obj_remove_event_dsc`.