How to disable self defined button from ALV Toolbar when ok_code ='BACK'

Question

here is the code
CLASS Z_CL_6_U_EVENT_RECEIVER DEFINITION.
  PUBLIC SECTION.
    METHODS:
      HANDLE_TOOLBAR
        FOR EVENT TOOLBAR OF CL_GUI_ALV_GRID
            IMPORTING E_OBJECT E_INTERACTIVE,
      HANDLE_USER_COMMAND
        FOR EVENT USER_COMMAND OF CL_GUI_ALV_GRID
            IMPORTING E_UCOMM.
ENDCLASS.         
CLASS  Z_CL_6_U_EVENT_RECEIVER IMPLEMENTATION.
  METHOD HANDLE_TOOLBAR.
DATA: LS_TOOLBAR  TYPE STB_BUTTON.
IF G_FLAG = 'X' and ok_code = space.
      CLEAR LS_TOOLBAR.
       MOVE 0 TO LS_TOOLBAR-BUTN_TYPE.
      MOVE 'UPDATE' TO LS_TOOLBAR-FUNCTION.
      MOVE  ICON_MODIFY  TO LS_TOOLBAR-ICON.
      MOVE 'Update Records'(111) TO LS_TOOLBAR-QUICKINFO.
      MOVE ''(112) TO LS_TOOLBAR-TEXT.
      MOVE ' ' TO LS_TOOLBAR-DISABLED.
      APPEND LS_TOOLBAR TO E_OBJECT->MT_TOOLBAR.
elseif ok_code = 'BACK'.
      CLEAR LS_TOOLBAR.
  LS_TOOLBAR-function = 'UPDATE'.
  LS_TOOLBAR-butn_type = 0.
  LS_TOOLBAR-icon = ICON_MODIFY.
  LS_TOOLBAR-quickinfo = 'Update Records'.
  LS_TOOLBAR-disabled = 'X'.
  append LS_TOOLBAR TO <i><b>E_OBJECT</b></i>->MT_TOOLBAR.
ENDIF.
  ENDMETHOD. 
<i><b>ERROR COMES when ok_code is 'BACK'.
at this point E_OBJECT has null reference instead of ref to Class cl_ALV_EVENT_TOOLBAR_SET.</b></i> 
tell me why this error coming.
pls help

Answer 1

Hello Neetu
To give you an example I have copied sample report BCALV_GRID_DEMO, added some code (search for <b>$Comment</b>) and modified the GUI-status <b>MAIN100</b> (replace function code EXIT with <b>BACK</b> for the F3 function).
Run the program and push several times the BACK button: one toolbar function after the other will be inactivated.
PROGRAM test.
DATA: ok_code LIKE sy-ucomm,
      gt_sflight TYPE TABLE OF sflight,
      g_container TYPE scrfname VALUE 'BCALV_GRID_DEMO_0100_CONT1',
      grid1  TYPE REF TO cl_gui_alv_grid,
      g_custom_container TYPE REF TO cl_gui_custom_container.
<b>----
      CLASS lcl_eventhandler DEFINITION
CLASS lcl_eventhandler DEFINITION.
  PUBLIC SECTION.
    CLASS-DATA:
      md_cnt    TYPE i.
    CLASS-METHODS:
      handle_toolbar FOR EVENT toolbar OF cl_gui_alv_grid
        IMPORTING
          e_object
          e_interactive
          sender.
ENDCLASS.                    "lcl_eventhandler DEFINITION
      CLASS lcl_eventhandler IMPLEMENTATION
CLASS lcl_eventhandler IMPLEMENTATION.
  METHOD handle_toolbar.
    DATA:
      ls_button    TYPE stb_button.
    ADD 1 TO md_cnt. " a simple counter
    LOOP AT e_object->mt_toolbar INTO ls_button FROM 1 TO md_cnt.
      ls_button-disabled = 'X'.
      MODIFY e_object->mt_toolbar FROM ls_button.
    ENDLOOP.
  ENDMETHOD.                    "handle_toolbar
ENDCLASS.                    "lcl_eventhandler IMPLEMENTATION</b>
START-OF-SELECTION.
*       MAIN                                                          *
  SELECT * FROM sflight INTO TABLE gt_sflight.
  CALL SCREEN 100.
*       MODULE PBO OUTPUT                                             *
MODULE pbo OUTPUT.
  SET PF-STATUS 'MAIN100'.
  IF g_custom_container IS INITIAL.
    CREATE OBJECT g_custom_container
           EXPORTING container_name = g_container.
*   Instantiate ALV grid control
    CREATE OBJECT grid1
           EXPORTING i_parent = g_custom_container.
    CALL METHOD grid1->set_table_for_first_display
      EXPORTING
        i_structure_name = 'SFLIGHT'
      CHANGING
        it_outtab        = gt_sflight.
<b>*$Comment: Set event handler for event TOOLBAR
    SET HANDLER:
      lcl_eventhandler=>handle_toolbar FOR grid1.
  ENDIF.</b>
ENDMODULE.                    "PBO OUTPUT
*       MODULE PAI INPUT                                              *
MODULE pai INPUT.
*   to react on oi_custom_events:
  CALL METHOD cl_gui_cfw=>dispatch.
  CASE ok_code.
    WHEN 'EXIT'.
      PERFORM exit_program.
<b>    WHEN 'BACK'.
$Comment: Toolbar can be modified on-the-fly
      grid1->set_toolbar_interactive( ).</b>
    WHEN OTHERS.
*     do nothing
  ENDCASE.
  CLEAR ok_code.
ENDMODULE.                    "PAI INPUT
*       FORM EXIT_PROGRAM                                             *
FORM exit_program.
*  CALL METHOD G_CUSTOM_CONTAINER->FREE.
*  CALL METHOD CL_GUI_CFW=>FLUSH.
  LEAVE PROGRAM.
ENDFORM.                    "EXIT_PROGRAM
Regards
  Uwe