Expand- Collapse Button in Selection Screen

REPORT ZRR_SAMPLE.

DATA: wf_ucomm TYPE sy-ucomm.

SELECTION-SCREEN BEGIN OF BLOCK b1 WITH FRAME.
SELECTION-SCREEN PUSHBUTTON  /01(30) but1 USER-COMMAND but1.
SELECTION-SCREEN PUSHBUTTON  /01(30) but2 USER-COMMAND but2.
PARAMETERS: p_test TYPE c.
SELECTION-SCREEN END OF BLOCK b1.

INITIALIZATION.
  CALL FUNCTION 'ICON_CREATE'
    EXPORTING
      name   = 'ICON_EXPAND'
    IMPORTING
      RESULT = but1
    EXCEPTIONS
      OTHERS = 0.
  CALL FUNCTION 'ICON_CREATE'
    EXPORTING
      name   = 'ICON_COLLAPSE'
    IMPORTING
      RESULT = but2
    EXCEPTIONS
      OTHERS = 0.

AT SELECTION-SCREEN.

  IF sy-ucomm EQ 'BUT1'.
    wf_ucomm = 'BUT1'.
  ELSEIF sy-ucomm EQ 'BUT2'.
    wf_ucomm = 'BUT2'.
  ENDIF.

AT SELECTION-SCREEN OUTPUT.

  IF wf_ucomm IS INITIAL.
    LOOP AT SCREEN.
      IF screen-name CS 'P_TEST' OR
         screen-name EQ 'BUT2'.
        screen-active = 0.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.
  ELSEIF wf_ucomm EQ 'BUT1'.
    LOOP AT SCREEN.
      IF screen-name CS 'P_TEST' OR
         screen-name EQ 'BUT2'.
        screen-active = 1.
        MODIFY SCREEN.
      ENDIF.
      IF screen-name EQ 'BUT1'.
        screen-active = 0.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.
  ELSEIF wf_ucomm EQ 'BUT2' .
    LOOP AT SCREEN.
      IF screen-name CS 'P_TEST' OR
         screen-name EQ 'BUT2'.
        screen-active = 0.
        MODIFY SCREEN.
      ENDIF.
      IF screen-name EQ 'BUT1'.
        screen-active = 1.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.
  ENDIF.