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Build ALV fieldcat from any structure

Use RTTI to generate a complete SLIS_T_FIELDCAT_ALV automatically — no hard-coded column definitions.

Purpose

Hand-coding a field catalog for every ALV report is tedious and brittle: adding a field to the structure means editing the catalog too. This pattern introspects the structure at runtime using RTTI (CL_ABAP_STRUCTDESCR) and builds the full field catalog — column labels, output lengths, DDIC texts — in a single reusable function module call.

Because the catalog is derived from the actual ABAP dictionary type, column headers come from the DDIC short/medium/long texts automatically. The caller passes any flat structure (work area of the internal table they want to display) and gets back a ready-to-use field catalog.

Signature

Parameter Direction Type Notes
I_STRUC IMPORTING ANY (pass by reference) A work area typed like the internal table you will display.
I_TABNAME IMPORTING CHAR50 (optional) Written into TABNAME of every catalog entry. Needed for F4 help on some ALV variants.
E_FCAT EXPORTING SLIS_T_FIELDCAT_ALV The generated field catalog, ready to pass to REUSE_ALV_GRID_DISPLAY.

How it works

The function module walks through four RTTI calls:

  1. CL_ABAP_STRUCTDESCR=>describe_by_data_ref — obtain a structure descriptor from a data reference. components gives you every field name and its raw byte length.
  2. lcl_descr->get_component_type — retrieve the type descriptor for a single component by name.
  3. lcl_typedescr->get_relative_name — get the DDIC type name (e.g. MATNR, MENGE) as a string so it can be resolved.
  4. CL_ABAP_ELEMDESCR=>describe_by_name + get_ddic_field — fetch the full DFIES record, which carries scrtext_s/m/l, reptext, and outputlen from the DDIC.

The resulting DFIES data is mapped into a SLIS_FIELDCAT_ALV entry via MOVE-CORRESPONDING, then the text fields and position are set explicitly.

Full implementation

FUNCTION z_build_fieldcat_from_struct.
*"----------------------------------------------------------------------
*"  IMPORTING
*"     REFERENCE(I_STRUC)   TYPE ANY
*"     REFERENCE(I_TABNAME) TYPE CHAR50 OPTIONAL
*"  EXPORTING
*"     REFERENCE(E_FCAT)    TYPE SLIS_T_FIELDCAT_ALV
*"----------------------------------------------------------------------

  DATA: lv_pos       TYPE i,
        lw_dfies     TYPE dfies,
        lt_fieldcat  TYPE slis_t_fieldcat_alv,
        lv_name      TYPE string.

  FIELD-SYMBOLS: <l_fcat> LIKE LINE OF lt_fieldcat,
                 <l_comp> TYPE abap_compdescr.

  DATA: lo_struct  TYPE REF TO cl_abap_structdescr,
        lo_elem    TYPE REF TO cl_abap_elemdescr,
        lo_type    TYPE REF TO cl_abap_typedescr,
        lo_ref     TYPE REF TO data.

  GET REFERENCE OF i_struc INTO lo_ref.

  lo_struct ?= cl_abap_structdescr=>describe_by_data_ref( lo_ref ).

  LOOP AT lo_struct->components ASSIGNING <l_comp>.

    lo_struct->get_component_type(
      EXPORTING p_name      = <l_comp>-name
      RECEIVING p_descr_ref = lo_type
      EXCEPTIONS OTHERS     = 1 ).

    IF sy-subrc <> 0.
      EXIT.
    ENDIF.

    lo_type->get_relative_name(
      RECEIVING p_relative_name = lv_name ).

    lo_elem ?= cl_abap_typedescr=>describe_by_name( lv_name ).

    lo_elem->get_ddic_field(
      EXPORTING p_langu    = sy-langu
      RECEIVING p_flddescr = lw_dfies
      EXCEPTIONS OTHERS    = 3 ).

    APPEND INITIAL LINE TO lt_fieldcat ASSIGNING <l_fcat>.
    ADD 1 TO lv_pos.

    MOVE-CORRESPONDING lw_dfies TO <l_fcat>.

    <l_fcat>-fieldname     = <l_comp>-name.
    <l_fcat>-outputlen     = <l_comp>-length.
    <l_fcat>-ddic_outputlen = lw_dfies-outputlen.
    <l_fcat>-seltext_s     = lw_dfies-scrtext_s.
    <l_fcat>-seltext_m     = lw_dfies-scrtext_m.
    <l_fcat>-seltext_l     = lw_dfies-scrtext_l.
    <l_fcat>-reptext_ddic  = lw_dfies-reptext.
    <l_fcat>-col_pos       = lv_pos.
    <l_fcat>-tabname       = i_tabname.

  ENDLOOP.

  e_fcat[] = lt_fieldcat.

ENDFUNCTION.

Example — display MARA with auto-generated catalog

REPORT z_demo_dynamic_alv.

DATA: lt_mara   TYPE STANDARD TABLE OF mara,
      ls_mara   TYPE mara,
      lt_fcat   TYPE slis_t_fieldcat_alv.

START-OF-SELECTION.

  SELECT * FROM mara INTO TABLE lt_mara UP TO 50 ROWS.

  " Pass a work area typed like the table — the FM inspects it at runtime
  CALL FUNCTION 'Z_BUILD_FIELDCAT_FROM_STRUCT'
    EXPORTING
      i_struc   = ls_mara
      i_tabname = 'MARA'
    IMPORTING
      e_fcat    = lt_fcat.

  CALL FUNCTION 'REUSE_ALV_GRID_DISPLAY'
    EXPORTING
      it_fieldcat = lt_fcat
    TABLES
      t_outtab    = lt_mara
    EXCEPTIONS
      OTHERS      = 1.

Common pitfalls

Non-DDIC fields are skipped silently

get_ddic_field raises no_ddic_type for local types (e.g. a CHAR10 field defined inline with TYPES rather than as a DDIC data element). The current implementation does not raise an exception in that case — the field still appears in the catalog but with no label text. Add explicit label assignment for any local-type fields, or exclude them.

Nested structures are not flattened

If your work area contains a nested structure (e.g. INCLUDE TYPE address_line), components returns the nested component as a single entry whose type is CL_ABAP_STRUCTDESCR, not CL_ABAP_ELEMDESCR. The ?= cast to lo_elem will throw CX_SY_MOVE_CAST_ERROR. Either flatten the structure before passing it in, or add a type check (lo_type->kind = cl_abap_typedescr=>kind_elem) before casting.

Works best with pure DDIC types

The richest output (correct output lengths, all label variants, currency/quantity reference fields) comes from structures built entirely from DDIC data elements. Structures that mix DDIC types with locally-defined ones will have partial metadata.

  • Column order matches the field order in the structure, controlled by lv_pos. Reorder the structure or adjust col_pos afterwards if a different display order is needed.
  • CL_SALV_TABLE alternative: if you switch to CL_SALV_TABLE instead of REUSE_ALV_GRID_DISPLAY, the catalog is not needed — factory builds its own column list automatically. This function module is specifically for the classic FM-based ALV.

See also

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