[ABAP] Show/Hide Fields with Radio Buttons

TABLES: ekpo.

* --------------------------------------------------------------------------------
* SELECTION-SCREEN
* --------------------------------------------------------------------------------

SELECTION-SCREEN BEGIN OF BLOCK b1 WITH FRAME TITLE TEXT-003.

PARAMETERS: p_a RADIOBUTTON GROUP rb1 USER-COMMAND action DEFAULT 'X',
            p_b RADIOBUTTON GROUP rb1.

SELECT-OPTIONS: s_a FOR ekpo-ebeln MODIF ID a,
                s_b FOR ekpo-ebelp MODIF ID b.

SELECTION-SCREEN END OF BLOCK b1.

AT SELECTION-SCREEN OUTPUT.
  PERFORM: update_screen.
  
* --------------------------------------------------------------------------------
* UPDATE-SCREEN
* --------------------------------------------------------------------------------
  
FORM update_screen.

  LOOP AT SCREEN.

    CASE abap_true.

      WHEN p_b.
        IF screen-group1     = 'A'.
          screen-active = '0'.
          MODIFY SCREEN.
        ELSEIF screen-group1 = 'B'.
          screen-active = '1'.
          MODIFY SCREEN.
        ENDIF.

      WHEN p_a.
        IF screen-group1     = 'A'.
          screen-active = '1'.
          MODIFY SCREEN.
        ELSEIF screen-group1 = 'B'.
          screen-active = '0'.
          MODIFY SCREEN.
        ENDIF.

    ENDCASE.
  ENDLOOP.
ENDFORM.