For example:
doc = ThisComponent
form = doc.DrawPage.Forms.getByName("MainForm")
list = form.getByName("lst_students")
Msgbox list.SelectedValue
But, if you call code from other control in the same form, you can access form with:
Sub cmd_selected_studen(event)
form = event.Source.Model.Parent
list = form.getByName("lst_students")
Msgbox list.SelectedValue
End Sub
Get selected position:
form = event.Source.Model.Parent
list = form.getByName("lst_students")
list_view = ThisComponent.CurrentController.getControl(list)
Msgbox list_view.SelectedItemPos