Ctrl_List_Box - How to get all currently selected Items

I'm lost in research on this matter and haven't so far found a similar problem here in the forums:

I have a Ctrl_List_Box in one of my screens. Here users can tick items in a list. So far so good. When I launch DlgListBox.GetSelected(CTRL_LIST_BOX_01) it only returns the last activated item.
I want to know which items were selected when advancing into the next screen.
Any help is appreciated, thanks in advance !