Dialog Closed Event from Custom URL built using APEX_UTIL.PREPARE_URL
But, when your dialog page URL is built using APEX_UTIL.PREPARE_URL, and you want to call Dialog Closed event? This will by default not detected with any of your dialog close selector.
So, purpose of this blog is to introduce you "p_triggering_element" parameter in APEX_UTIL.PREPARE_URL function. You have to set value of this parameter something like "apex.jQuery('#<your_parent_region_static_id>')".
This will now detect On Dialog Close event with your parent region as a Selection Type in dynamic action configuration.
Hope this helps!