For many years we have written dialog item hook functions using procedural code. You can continue that way with MicroStation CONNECT, but the MicroStationAPI offers a better way: dialog and dialog item hook classes.
The hook classes replace the MDL switch decision tree with the DialogHookHandler and DialogItemHookHandler classes that provides virtual event handler methods such as _OnCreate(). The ListModelManager class goes one step further: it provides dialog item specific methods to assign and deallocate the ListModel using by ComboBox and ListBox dialog items.
ListModelManager is a template class. It offers specialised handlers for ComboBox and ListBox dialog items. They improve your code by using the correct set/get methods and by always destroying the ListModel in the _OnDestroy() event.