Multiple select options validation at selection screen

Question

Hi,
I have the requirement to create a selection screen with 3 select options. Two of them are cross-dependent. It is mandatory to fill one of them and it is not allowed to fill both. The third one is optional. I tried the validation at selection-screen on block... and I have a problem that search help buttons for select options react like execution buttons, when I press any of them I am getting one of errors instead of search help.
Any help on this issue would be appreciated.
Here is my code:
DATA:
      so_rbkp TYPE rbkp,
      so_mseg TYPE mseg.
SELECTION-SCREEN BEGIN OF BLOCK blok WITH FRAME.
  SELECT-OPTIONS:
        s_fakt   FOR so_rbkp-belnr,
        s_matdok FOR so_mseg-mblnr,
        s_god FOR so_mseg-gjahr.
SELECTION-SCREEN END OF BLOCK blok.
INITIALIZATION.
SET TITLEBAR '0100'.
START-OF-SELECTION.
  AT SELECTION-SCREEN on block blok.
      if s_fakt <> space and s_matdok <> space.
        MESSAGE 'Message1' TYPE 'E'.
      elseif s_fakt = space and s_matdok = space.
        MESSAGE 'Message2' TYPE 'E'.
      endif.
    ENDIF.

Answer 1

Only perform the check when user wants to execute or submit the program, not when pressing F4 or even Enter, but in a selection-screen event, before START-OF-SELECTION which were program would terminate in error :
TABLES: SSCRFIELDS.
AT SELECTION-SCREEN OB BLOCK b01.
    IF sscrfields-ucomm EQ 'ONLI'
    OR sscrfields-ucomm EQ 'PRIN'
    OR sscrfields-ucomm EQ 'SJOB'.
      IF s_fakt[] IS NOT INITIAL AND s_matdok IS NOT INITIAL.
        MESSAGE 'Message1' TYPE 'E'.
      ELSEIF s_fakt[] IS INITIAL and s_matdok[] IS INITIAL.
        MESSAGE 'Message2' TYPE 'E'.
      ENDIF.
    ENDIF.
(You could also always send the message, but using type 'E' for those function code and 'S' status for any other value.)
Regards,
Raymond