You have to override the get_sorted_list member, it has to return an array
sorted by the constraints you establish.
_init (\midcom_helper_nav $nap, integer $parent_topic_id)
Initialize the object, used by the factory function.
\midcom_helper_navA reference to a NAP object to use.
integerA ID of the topic in which we operate.
factory ($sorting, \midcom_helper_nav $nap, $parent_topic)
Returns the sorted list for this topic according to our sorting criteria.
It has to be overridden. Throw midcom_error on any critical failure.
ArrayAn array of all objects.
A reference to the NAP instance we belong to.