On-value request and cl_abap_structdescr

Question

Hi,
I want to use on-value request to get the field names of a table, but I can't make it work.
I already tried finding a solution on the forum but without success.
This is my code:
DATA:
      lt_order  TYPE TABLE OF crmd_orderadm_h,
      g_container TYPE scrfname VALUE 'G_CONTAINER',
      g_filter  TYPE string,
      g_custom_container TYPE REF TO cl_gui_custom_container,
      g_grid TYPE REF TO cl_gui_alv_grid,
      ls_variant TYPE disvariant,
      lv_select TYPE string,
      lr_struct TYPE REF TO cl_abap_structdescr,
      lt_tab    TYPE ddfields.
SELECTION-SCREEN BEGIN OF BLOCK sel1 WITH FRAME TITLE text-123.
PARAMETERS:
            p_number  TYPE  i,
            p_fname   TYPE string,
            p_varian TYPE c AS CHECKBOX.
SELECTION-SCREEN END OF BLOCK sel1.
AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_fname.
  CALL METHOD lr_struct->get_ddic_field_list
    EXPORTING
      p_langu                  = SY-LANGU
      p_including_substructres = ABAP_FALSE
    receiving
      p_field_list             = lt_tab
    EXCEPTIONS
      not_found                = 1
      no_ddic_type             = 2
      others                   = 3
If u run my program and press F4 I get the following error:
Runtime Errors         OBJECTS_OBJREF_NOT_ASSIGNED
Except.                CX_SY_REF_IS_INITIAL       
Short text                                             
    Access via 'NULL' object reference not possible. 
This is where it goes wrong:  CALL METHOD lr_struct->get_ddic_field_list
What do i need to do with lr_struct before the method call?
Edited by: Kevv00 on Sep 20, 2011 4:11 PM

Answer 1

lr_struct ?= CL_ABAP_STRUCTDESCR=>describe_by_name( p_name = 'crmd_orderadm_h' ).
thanks, but I'm still missing something because it doesn't do anything now.. when I click it twice I get this in the status bar: 'Function code cannot be selected'
Could you also explain the method DESCRIBE_BY_NAME please? I tried the description but I don't understand what it actually does.
Maybe I misplaced the at selection screen code? This is my whole program:
DATA:
      lt_order  TYPE TABLE OF crmd_orderadm_h,
      g_container TYPE scrfname VALUE 'G_CONTAINER',
      g_filter  TYPE string,
      g_custom_container TYPE REF TO cl_gui_custom_container,
      g_grid TYPE REF TO cl_gui_alv_grid,
      ls_variant TYPE disvariant,
      lv_select TYPE string,
      lr_struct TYPE REF TO cl_abap_structdescr,
      lt_tab    TYPE ddfields.
SELECTION-SCREEN BEGIN OF BLOCK sel1 WITH FRAME TITLE text-123.
PARAMETERS:
            p_number  TYPE  i,
            p_fname   TYPE string,
            p_varian TYPE c AS CHECKBOX.
SELECTION-SCREEN END OF BLOCK sel1.
AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_fname.
  lr_struct ?= CL_ABAP_STRUCTDESCR=>describe_by_name( p_name = 'crmd_orderadm_h' ).
  CALL METHOD lr_struct->get_ddic_field_list
    EXPORTING
      p_langu                  = SY-LANGU
      p_including_substructres = ABAP_FALSE
    receiving
      p_field_list             = lt_tab
    EXCEPTIONS
      not_found                = 1
      no_ddic_type             = 2
      others                   = 3
  FORM subr_select.
  CONCATENATE '%' g_filter '%' INTO lv_select.
  SELECT (p_fname)
  FROM crmd_orderadm_h
  INTO CORRESPONDING FIELDS OF TABLE lt_order
  UP TO p_number ROWS
  WHERE description LIKE lv_select.
ENDFORM.                    "subr_select
START-OF-SELECTION.
  PERFORM subr_select.
  IF p_varian = 'X'.
    ls_variant-variant = '/ZSTD8'.
  ENDIF.
  IF g_grid IS INITIAL.
    CREATE OBJECT g_custom_container
      EXPORTING
        container_name = g_container.
    CREATE OBJECT g_grid
      EXPORTING
        i_parent = g_custom_container.
    ls_variant-report = sy-cprog.
    CALL METHOD g_grid->set_table_for_first_display
      EXPORTING
        i_structure_name              = 'CRMD_ORDERADM_H'
        is_variant                    = ls_variant
        i_save                        = 'A'
      CHANGING
        it_outtab                     = lt_order
      EXCEPTIONS
        invalid_parameter_combination = 1
        program_error                 = 2
        too_many_lines                = 3
        OTHERS                        = 4.
  ELSE.
    CALL METHOD g_grid->refresh_table_display
*     EXPORTING
*       is_stable      =
*       i_soft_refresh =
      EXCEPTIONS
        finished       = 1
        OTHERS         = 2
  ENDIF.
  CALL SCREEN 100.
  INCLUDE zst08_alv_ex1_status_0100o02.
  INCLUDE zst08_alv_ex1_user_command_i01.