Column Heading are not displayed in ALV Report using CL_SALV_DISPLAY?

Question

Hi,
   I am using CL_SALV_DISPLAY class to display data. I Created an Internal Table Dynamically based fieldcatalog which was prepared based data at run time. When i displayed data using CL_SALC_DISPALY data is display in output but column headings are not displayed.
can anyone suggest me how to display heading in ALV using CL_SALV_DISPLAY class, My code is
      CLASS lcl_report DEFINITION
CLASS lcl_report DEFINITION.
  PUBLIC SECTION.
    METHODS:
      display  IMPORTING l_table  TYPE string
                         l_fcat   TYPE string.
ENDCLASS.                    "lcl_report DEFINITION
      CLASS lcl_report IMPLEMENTATION
CLASS lcl_report IMPLEMENTATION.
  METHOD display.
    DATA: gr_table   TYPE REF TO cl_salv_table.
    DATA: gr_columns TYPE REF TO cl_salv_columns_table,
          gr_column  TYPE REF TO cl_salv_column_table,
          ls_fcat    TYPE slis_fieldcat_alv.
    DATA: gr_display TYPE REF TO cl_salv_display_settings.
    DATA: l_o_functions TYPE REF TO cl_salv_functions_list,
          l_field    TYPE string.
    FIELD-SYMBOLS : <fs_table>    TYPE STANDARD TABLE,
                    <ft_fcat>     TYPE STANDARD TABLE.
Get the ALV object refering to the output table
    ASSIGN (l_table) TO <fs_table>.
    ASSIGN (l_fcat)  TO <ft_fcat>.
    TRY.
        cl_salv_table=>factory(
          IMPORTING
            r_salv_table = gr_table
          CHANGING
            t_table      = <fs_table> ).
      CATCH cx_salv_msg.                                "#EC NO_HANDLER
    ENDTRY.
Add basic default functionality in the ALV report
Functions
    l_o_functions = gr_table->get_functions( ).
    l_o_functions->set_all( abap_true ).
    gr_columns = gr_table->get_columns( ).
    gr_columns->set_headers_visible( abap_true ).
Display the list
    gr_table->display( ).
  ENDMETHOD.                    "extract
ENDCLASS.                    "lcl_report IMPLEMENTATION
*& start-of-selection declaration
START-OF-SELECTION.
  PERFORM :
  get store codes
    get_storecodes    USING      p_stfile
                      CHANGING   it_t001w,
  fetching mard data
    read_mard_data,
  preparing fieldcatalog for Final Data
    create_filedcat   USING      it_t001w
                                 it_site
                      CHANGING   it_fieldcat,
  preparing structure & internal table for Final Data
    create_final_table_structure  USING  it_fieldcat,
  prepare output data
    prepare_final_data.
*& end-of-selection declaration
END-OF-SELECTION.
  PERFORM :
  display data
    display_data    USING l_table
                          l_fcat.
*&      Form  get_storecodes
FORM get_storecodes  USING    p_p_stfile
                     CHANGING p_it_t001w  LIKE it_t001w[].
  DATA  :
internal table for RAW
  lt_raw    TYPE truxs_t_text_data,
  rs_site   LIKE LINE OF rt_site,
  l_index   LIKE sy-tabix.
  FIELD-SYMBOLS :
field symbol for it_t001w
  <fs_t001w>   LIKE LINE OF p_it_t001w.
calling function module to get Stores Data from File
  CALL FUNCTION 'TEXT_CONVERT_XLS_TO_SAP'
    EXPORTING
      i_line_header        = 'X'
      i_tab_raw_data       = lt_raw
      i_filename           = p_p_stfile
    TABLES
      i_tab_converted_data = p_it_t001w[]
    EXCEPTIONS
      conversion_failed    = 1
      OTHERS               = 2.
  IF sy-subrc <> 0.
    EXIT.
  ENDIF.
  SORT p_it_t001w BY werks.
  CLEAR rs_site.
  rs_site-sign   = 'I'.
  rs_site-option = 'EQ'.
  rs_site-low    = p_dccode.
  APPEND rs_site TO rt_site.
  IF it_t001w[] IS NOT INITIAL.
    LOOP AT p_it_t001w ASSIGNING <fs_t001w>.
      l_index   = sy-tabix.
      CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'
        EXPORTING
          input  = <fs_t001w>-werks
        IMPORTING
          output = <fs_t001w>-werks.
      MODIFY p_it_t001w FROM <fs_t001w> INDEX l_index.
      IF <fs_t001w>-werks GE s_site-low AND <fs_t001w>-werks LE s_site-high.
      append site to ranges
        CLEAR rs_site.
        rs_site-sign   = 'I'.
        rs_site-option = 'EQ'.
        rs_site-low    = <fs_t001w>-werks.
        APPEND rs_site TO rt_site.
        CONTINUE.
      ENDIF.
    ENDLOOP.
    SORT p_it_t001w BY werks.
    SORT rt_site.
  ENDIF.
ENDFORM.                    " get_storecodes
*&      Form  create_final_table_structure
FORM create_filedcat   USING    p_it_t001w      LIKE it_t001w[]
                                p_it_site       LIKE it_site[]
                       CHANGING p_it_fieldcat   LIKE it_fieldcat[].
  FIELD-SYMBOLS :
field symbol for p_it_t001w
  <fs_t001w>     LIKE LINE OF p_it_t001w,
field symbol for p_it_site
  <fs_site>      LIKE LINE OF p_it_site.
  DATA :
fieldname
  l_fieldname    TYPE slis_fieldname,
workarea for site ranges
  rs_site        LIKE LINE OF rt_site.
  CLEAR : l_fieldname, rs_site.
  l_fieldname    = p_dccode.
  PERFORM
prepare fieldcatalog
  build_fieldcatalog USING :   'MTART'      'CHAR'        '5'  ,
                               'MTBEZ'      'CHAR'        '25' ,
                               'MATKL'      'CHAR'        '6'  ,
                               'WGBEZ'      'CHAR'        '20' ,
                               'MATNR'      'CHAR'        '18' ,
                               'MAKTX'      'CHAR'        '30' ,
                                l_fieldname 'CHAR'        '17' .
create header for excel
  PERFORM create_excel_header USING  : 'Division',
                                       'Divsion Description',
                                       'MC Code',
                                       'MC Description',
                                       'Article',
                                       'Article Description',
                                        l_fieldname.
loop for creating fieldcatalog
  LOOP AT it_site ASSIGNING <fs_site>.
    READ TABLE it_t001w ASSIGNING <fs_t001w> WITH KEY werks = <fs_site>-werks
                                                              BINARY SEARCH.
    IF sy-subrc = 0           AND <fs_t001w> IS ASSIGNED AND
       <fs_site> IS ASSIGNED  AND <fs_site>-stock GT 0.
      CLEAR : l_fieldname, rs_site.
      l_fieldname    = <fs_site>-werks.
    prepare fieldcatalog
      PERFORM build_fieldcatalog USING : l_fieldname    'CHAR'   '17'.
    create header for excel
      PERFORM create_excel_header USING  l_fieldname  .
      CONTINUE.
    ENDIF.
  ENDLOOP.
  l_fcat  = 'it_fieldcat[]'.
ENDFORM.                    " create_final_table_structure
*&      Form  build_fieldcatalog
FORM build_fieldcatalog  USING    p_fieldname      TYPE slis_fieldname
                                  p_datatype       TYPE datatype_d
                                  p_length         TYPE intlen.
  DATA : ls_fieldcat    LIKE LINE OF it_fieldcat.
  CLEAR  : ls_fieldcat.
  ls_fieldcat-fieldname   = p_fieldname.
  ls_fieldcat-datatype    = p_datatype.
  ls_fieldcat-intlen      = p_length.
  APPEND ls_fieldcat TO it_fieldcat.
ENDFORM.                    " build_fieldcatalog
*&      Form  create_final_table_structure
FORM create_final_table_structure  USING    p_it_fieldcat.
Create dynamic internal table and assign to FS
  CALL METHOD cl_alv_table_create=>create_dynamic_table
    EXPORTING
      it_fieldcatalog = it_fieldcat
    IMPORTING
      ep_table        = t_table.
  ASSIGN t_table->*  TO <ft_final>.
ENDFORM.                    " create_final_table_structure
*&      Form  create_excel_header
FORM create_excel_header  USING    p_p_fieldname.
  DATA : ls_header  LIKE LINE OF it_header.
  CLEAR ls_header.
  ls_header-col_name  = p_p_fieldname.
  APPEND ls_header TO it_header.
ENDFORM.                    " create_excel_header
*&      Form  prepare_final_data
FORM prepare_final_data .
  DATA          : l_matnr       LIKE g_matnr,
                  l_werks       LIKE g_werks,
                  l_index       LIKE sy-tabix.
  FIELD-SYMBOLS : <fs_mard>     LIKE LINE OF it_mard.
Getting No. of Lines in IT_MARD internal table
  DESCRIBE TABLE it_mard LINES g_lines.
  LOOP AT it_mard ASSIGNING <fs_mard>.
    l_index    = sy-tabix.
    IF l_matnr IS INITIAL.
      l_matnr  = <fs_mard>-matnr.
      CLEAR : l_werks.
      l_werks    = <fs_mard>-werks.
      UNASSIGN : <fs_value>, <fs_final>.
    Create dynamic work area and assign to FS
      CREATE DATA t_line LIKE LINE OF <ft_final>.
      ASSIGN t_line->*   TO <fs_final>.
      ASSIGN COMPONENT 'MATNR'  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_mard>-matnr.
      ASSIGN COMPONENT l_werks  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_value> + <fs_mard>-labst.
    getting Article Type,MC & its Descriptions
      PERFORM get_other_data    USING     l_matnr
                                          l_werks.
    ELSEIF l_matnr <> <fs_mard>-matnr.
      APPEND <fs_final> TO <ft_final>.
      CLEAR l_matnr.
      l_matnr  = <fs_mard>-matnr.
      CLEAR : l_werks.
      l_werks    = <fs_mard>-werks.
      UNASSIGN : <fs_value>, <fs_final>.
    Create dynamic work area and assign to FS
      CREATE DATA t_line LIKE LINE OF <ft_final>.
      ASSIGN t_line->*   TO <fs_final>.
      ASSIGN COMPONENT 'MATNR'  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_mard>-matnr.
      ASSIGN COMPONENT l_werks  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_value> + <fs_mard>-labst.
    getting Article Type,MC & its Descriptions
      PERFORM get_other_data    USING     l_matnr
                                         l_werks.
    ELSE.
      CLEAR : l_werks.
      l_werks    = <fs_mard>-werks.
      ASSIGN COMPONENT l_werks  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_value> + <fs_mard>-labst.
    ENDIF.
    IF l_index = g_lines.
      APPEND <fs_final> TO <ft_final>.
    ENDIF.
  ENDLOOP.
  l_table  = '<ft_final>[]'.
ENDFORM.                    " prepare_final_data
*&      Form  get_other_data
FORM get_other_data  USING    p_l_matnr
                              p_l_werks.
  FIELD-SYMBOLS : <fs_mara>     LIKE LINE OF it_mara,
                  <fs_t023t>    LIKE LINE OF it_t023t,
                  <fs_t134t>    LIKE LINE OF it_t134t,
                  <fs_makt>     LIKE LINE OF it_makt.
  READ TABLE it_mara ASSIGNING <fs_mara> WITH KEY matnr = p_l_matnr.   " BINARY SEARCH.
  IF sy-subrc = 0 AND <fs_mara> IS ASSIGNED.
    ASSIGN COMPONENT 'MTART'  OF STRUCTURE <fs_final> TO <fs_value>.
    <fs_value>        = <fs_mara>-mtart.
    ASSIGN COMPONENT 'MATKL'  OF STRUCTURE <fs_final> TO <fs_value>.
    <fs_value>        = <fs_mara>-matkl.
    READ TABLE it_makt  ASSIGNING <fs_makt>  WITH KEY matnr =  <fs_mara>-matnr   BINARY SEARCH.
    IF sy-subrc = 0 AND <fs_makt> IS ASSIGNED.
      ASSIGN COMPONENT 'MAKTX'  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>        = <fs_makt>-maktx.
    ENDIF.
    READ TABLE it_t023t ASSIGNING <fs_t023t> WITH KEY matkl = <fs_mara>-matkl  BINARY SEARCH.
    IF sy-subrc = 0 AND <fs_t023t> IS ASSIGNED.
      ASSIGN COMPONENT 'WGBEZ'  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>      = <fs_t023t>-wgbez.
    ENDIF.
    READ TABLE it_t134t ASSIGNING <fs_t134t> WITH KEY mtart = <fs_mara>-mtart  BINARY SEARCH.
    IF sy-subrc = 0 AND <fs_t134t> IS ASSIGNED.
      ASSIGN COMPONENT 'MTBEZ'  OF STRUCTURE <fs_final> TO <fs_value>.
      <fs_value>      = <fs_t134t>-mtbez.
    ENDIF.
  ENDIF.
ENDFORM.                    " get_other_data
*&      Form  display_data
      text
FORM display_data  USING    p_l_table
                            p_l_fcat.
  DATA:
Variable for Object Creation
  o_report TYPE REF TO lcl_report.
  CREATE OBJECT o_report.
  o_report->display( EXPORTING l_table = p_l_table
                               l_fcat  = p_l_fcat ).
ENDFORM.                    " display_data

Answer 1

I don't know how to read the code you pasted or I would have checked this myself.
Do your fields in the internal table reference dictionary objects or elementary types? If not using dictionary types, the column names will be blank by default. If you can't change your fields to be dictionary types, you can try this to change the column names:
I made a method inside my local class to add the names:
        call method set_colname
          EXPORTING iv_tab = alv_tab
                    iv_colid = 'xxxx'  "fieldname from the table
                    iv_stxt = text-t54
                    iv_mtxt = text-t55
                    iv_ltxt = text-t55.
METHOD set_colname .
  data:
          alv_cols type REF TO cl_salv_columns_table,
          alv_col type REF TO cl_salv_column.
  TRY .
*... Change fieldnames
        call METHOD iv_tab->get_columns RECEIVING value = alv_cols.
        call method alv_cols->get_column EXPORTING columnname = iv_colid RECEIVING value = alv_col.
        IF iv_stxt <> ''.
          CALL METHOD alv_col->set_short_text EXPORTING value = iv_stxt.
        ENDIF.
        IF iv_mtxt <> ''.
          CALL METHOD alv_col->set_medium_text EXPORTING value = iv_mtxt.
        ENDIF.
        IF iv_ltxt <> ''.
          CALL METHOD alv_col->set_long_text EXPORTING value = iv_ltxt.
        ENDIF.
   CATCH cx_salv_not_found.
  ENDTRY.
ENDMETHOD. "set_colname