Create Fieldcatalog based on internal table (dynamic)

Question

Hi ,
Is there a way to create Create Fieldcatalog based on internal table (dynamic).
while creating fieldcat we usually many give the fields "fieldname" and "tabname".
is there a way to get the fieldname from the main table ?
Eg ..
I have i_tab as the output table. It has 3 fields "a", "b" and "c"
Now when i created fieldcat manually ( in case i cannot use fieldcat_merge FM) , i have to append 3 throws in fieldcat table.
These rows would have "a", "b" and "c".
Now i want to know if there is a way in which i can find "a" "b" and "c" fieldnames from the createdd internal tables.
i can then append the same to fieldcat.

Answer 1

Hi Anuj,
I created a FORM routine for this 4 or 5 years ago and made a couple of refinements. Meanwhile it has prooved as very useful.
The disadvantag is that it creates the oldfashioned field catalog for the function calls. But I already used it for OO fieldcatalog of LVC type - there is a function module for this but I do not have the name here.
You need the two forms (second called in first) to build the field catalog from any internal table that can be used for ALV display.
*&      Form  ALV_FIELDCAT_FOR_ITAB
*       Feldkatalog from (arbitrary) internal Table (c) Clemens Li
*       * build field catalog from        type description
form alv_fieldcat_for_itab                                  "#EC *
  tables   pt_outtab                      type table        "#EC *
  changing pt_alv_fieldcat                type slis_t_fieldcat_alv."#EC *
  data:
    lv_desc                               type sydes_desc,
    ls_alv_fieldcat                       type slis_fieldcat_alv,
    lv_longfield                          type text80."CRM<=R/3 fname.
  field-symbols:
    <typeinfo>                            type sydes_typeinfo,
    <nameinfo>                            type sydes_nameinfo.
  describe field pt_outtab into lv_desc.                    "#EC *
  loop at lv_desc-types
      assigning <typeinfo>
      where not idx_name is initial
        and table_kind is initial "no entries for deep table like color
        and back                          = 1. "top-level-entries only.
    read table lv_desc-names index <typeinfo>-idx_name
      assigning <nameinfo>.
    check <nameinfo>-name                 <> 'INCLUDE'.
    ls_alv_fieldcat-fieldname             = <nameinfo>-name.
    while not <nameinfo>-continue is initial.
      add 1 to <typeinfo>-idx_name.
      read table lv_desc-names index <typeinfo>-idx_name
        assigning <nameinfo>.
      concatenate
        ls_alv_fieldcat-fieldname
        <nameinfo>-name
        into ls_alv_fieldcat-fieldname.
    endwhile." not <nameinfo>-continue IS INITIAL.
    read table lv_desc-names index <typeinfo>-idx_help_id
      assigning <nameinfo>.
    if sy-subrc                           = 0.
* Caution: Help-ID may be Tablename-Fieldname and thus longer
* than 30 Chars; ls_alv_fieldcat-rollname is 30 Chars only
      ls_alv_fieldcat-rollname            = <nameinfo>-name.
      lv_longfield                        = <nameinfo>-name.
      while not <nameinfo>-continue is initial.
        add 1 to <typeinfo>-idx_help_id.
        read table lv_desc-names index <typeinfo>-idx_help_id
          assigning <nameinfo>.
        concatenate
          lv_longfield
          <nameinfo>-name
          into lv_longfield.
      endwhile." not lv_desc-continue is initial.
* help id may be data element or <table>-<field>
      if lv_longfield ca '-'.
* get data                                type for table field
        perform get_rollname_4_tabfield
          using lv_longfield changing ls_alv_fieldcat.
      endif." lv_longfield ca '-'.
    else.
* No Help-ID: Use Fieldname as text
      ls_alv_fieldcat-seltext_s           =
      ls_alv_fieldcat-seltext_m           =
      ls_alv_fieldcat-seltext_l           =
      ls_alv_fieldcat-reptext_ddic        =
      <nameinfo>-name.
    endif." sy-subrc                      = 0.
* Starting 4.7: get edit mask
    if not <typeinfo>-idx_edit_mask is initial.
      read table lv_desc-names index <typeinfo>-idx_edit_mask
        assigning <nameinfo>.
      ls_alv_fieldcat-edit_mask           = <nameinfo>-name.
      if not <nameinfo>-continue is initial.
        add 1 to <typeinfo>-idx_edit_mask.
        read table lv_desc-names index <typeinfo>-idx_edit_mask
          assigning <nameinfo>.
        concatenate
          ls_alv_fieldcat-edit_mask
          <nameinfo>-name
          into ls_alv_fieldcat-edit_mask.
      endif." not <nameinfo>-continue IS INITIAL.
    endif." not <typeinfo>-IDX_EDIT_MASK is initial.
* assign length, output length and decimals
    ls_alv_fieldcat-intlen                = <typeinfo>-length.
    ls_alv_fieldcat-outputlen             = <typeinfo>-output_length.
    ls_alv_fieldcat-decimals_out          = <typeinfo>-decimals.
    ls_alv_fieldcat-inttype               = <typeinfo>-type.
    append ls_alv_fieldcat to pt_alv_fieldcat.
    clear:  "prevent anything 2 B  taken for subsequent fields
      ls_alv_fieldcat.
  endloop." at lv_desc-types where not IDX_NAME is in initial.
endform.                    " ALV_FIELDCAT_FOR_ITAB
*&      Form  get_rollname_4_tabfield
*       Get Data                          type for Table field
form get_rollname_4_tabfield
  using    p_fname                        type text80 ""CRM<=R/3 fname
  changing p_alv_fieldcat                 type slis_fieldcat_alv.
  field-symbols:
    <dfies>                               type dfies.
  data:
    lv_tabname                            type tabname,
     lt_dfies                             type table of dfies,
    lv_fieldname                          type fieldname.
  split p_fname at '-'
    into lv_tabname lv_fieldname.
  clear p_alv_fieldcat-rollname.
  call function 'DDIF_FIELDINFO_GET'
    exporting
      tabname                             = lv_tabname
      fieldname                           = lv_fieldname
*   LANGU                                 = SY-LANGU
*   LFIELDNAME                            = ' '
*   ALL_TYPES                             = ' '
* IMPORTING
*   X030L_WA                              =
*   DDOBJTYPE                             =
*   DFIES_WA                              =
*   LINES_DESCR                           =
   tables
     dfies_tab                            =  lt_dfies
*   FIXED_VALUES                          =
   exceptions
     not_found                            = 1
     internal_error                       = 2
     others                               = 3
  if sy-subrc                             <> 0.
    message id sy-msgid                   type sy-msgty number sy-msgno
            with sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
  else.
    read table   lt_dfies assigning <dfies> index 1.
    p_alv_fieldcat-rollname               = <dfies>-rollname.
* Und wenn keinerlei Twexte gepflegt sind?
    if <dfies>-reptext is initial and
       <dfies>-scrtext_s is initial and
       <dfies>-scrtext_m is initial and
       <dfies>-scrtext_l is initial.
* No Text: Use Fieldname as text
      p_alv_fieldcat-seltext_s            =
      p_alv_fieldcat-seltext_m            =
      p_alv_fieldcat-seltext_l            =
      p_alv_fieldcat-reptext_ddic         =
      p_alv_fieldcat-fieldname.
    endif." <dfies>-reptext IS INITIAL AND
  endif.
endform.                    " get_rollname_4_tabfield
Regards,
Clemens