Internal table structure/ALV Problem

Question

Hello, Im new to ABAP (third day) so careful explination would be greatly appreciated.
So I'm trying to display two tables together that I've joined into an ALV.  Im creating an internal table to hold the information that I want to display from the join I created. 
When I call my alv set_table_for_first_display I need to specify i_structure_name.  Right now im using the name of my internal table, but I dont know if im doing this right.  When I run my program i get an error NO_FIELDCATALOG_AVAILABLE.  After searching many other posts i think its because my internal table doesnt have a structure, but im not sure.
Here is my code, thanks in advance!:
CLASS application DEFINITION.
  PUBLIC SECTION.
    METHODS: constructor,
       read_data IMPORTING l_DAUAT TYPE AFPO-DAUAT,
       fill_list.
  PRIVATE SECTION.
    DATA: BEGIN OF tbljoin,
            AFPO_AUFNR TYPE AFPO-AUFNR,
            AFPO_DAUAT TYPE AFPO-DAUAT,
            AFPO_DGLTP TYPE AFPO-DGLTP,
            AFPO_DGLTS TYPE AFPO-DGLTS,
            AFPO_OBJNP TYPE AFPO-OBJNP,
            AFPO_XLOEK TYPE AFPO-XLOEK,
            AFKO_GLTRP TYPE AFKO-GLTRP,
    END OF tbljoin,
   afpo_tab TYPE TABLE OF afpo,
    join_tab LIKE STANDARD TABLE OF TBLJOIN,
    container TYPE REF TO cl_gui_custom_container,
    alv_list TYPE REF TO cl_gui_alv_grid.
ENDCLASS.
*Class Implementations
CLASS application IMPLEMENTATION.
  METHOD read_data.
    Select: POAUFNR PODAUAT PODGLTP PODGLTS POOBJNP POXLOEK
KO~GLTRP
    FROM afpo as po INNER JOIN AFKO as KO
      on POAUFNR = KOAUFNR
    INTO TABLE join_tab
    where dauat = l_dauat.
  ENDMETHOD.
  METHOD constructor.
    CREATE OBJECT container
        EXPORTING container_name = 'LIST_AREA'.
    CREATE OBJECT alv_list
        EXPORTING i_parent = container.
      CALL METHOD alv_list->set_table_for_first_display
        EXPORTING i_structure_name = 'JOINTAB'
        CHANGING it_outtab = join_tab.
  ENDMETHOD.
  METHOD fill_list.
    CALL METHOD alv_list->refresh_table_display.
  ENDMETHOD.
ENDCLASS.
DATA: object_ref TYPE REF TO application.
*Screens Interfaces
TABLES: AFPO, AFKO.
*Processing Blocks called by the Runtime Environment             *
*Event Block START-OF-SELECTION
START-OF-SELECTION.
  CREATE OBJECT object_ref.
  CALL SCREEN 100.
*Dialog Module PBO
MODULE status_0100 OUTPUT.
  SET PF-STATUS 'SCREEN_100'.
  CALL METHOD object_ref->fill_list.
ENDMODULE.
*Dialog Module PAI
MODULE user_command_0100 INPUT.
  IF sy-ucomm = 'BACK' OR
     sy-ucomm = 'EXIT' OR
     sy-ucomm = 'CANCEL'.
    LEAVE PROGRAM.
  ELSE.
    CALL METHOD object_ref->read_data
        EXPORTING l_dauat = afpo-dauat.
  ENDIF.
ENDMODULE.

Answer 1

Hi Nathan,
Fieldcatalog has important role in ALV .U missed that one .Go through these steps.
<b>1</b>.
Define ur Fieldcatalog table like this .
DATA:
  i_field   TYPE lvc_t_fcat,
  w_field   TYPE lvc_s_fcat.
<b>2</b>.
Build like this
FORM build_fieldcatalog_tab .
  DATA :pos TYPE i VALUE 1.
  CLEAR: w_field,i_field[],pos.
  w_field-col_pos   = pos  + 1.
  w_field-fieldname = 'MATNR' .
  w_field-tabname   = 'I_MARC' .
  w_field-scrtext_m = 'Material' .
  APPEND w_field TO i_field.
  CLEAR w_field.
  w_field-col_pos   = pos  + 1.
  w_field-fieldname = 'WERKS' .
  w_field-tabname   = 'I_MARC' .
  w_field-scrtext_m = 'Plant' .
  APPEND w_field TO i_field.
  CLEAR w_field.
ENDFORM.
<b>3</b>.
Pass through this method
<b>  CALL METHOD alv_grid->set_table_for_first_display</b>
    EXPORTING
     I_BUFFER_ACTIVE               =
     I_BYPASSING_BUFFER            =
     I_CONSISTENCY_CHECK           =
     i_structure_name              = 'MARA'
     IS_VARIANT                    =
     I_SAVE                        =
     I_DEFAULT                     = 'X'
       is_layout                     = w_layout
     IS_PRINT                      = w_print
     IT_SPECIAL_GROUPS             =
     IT_TOOLBAR_EXCLUDING          =
     IT_HYPERLINK                  =
     IT_ALV_GRAPHICS               =
     IT_EXCEPT_QINFO               =
    CHANGING
<b>     it_outtab                     = i_marc</b>
<b>     it_fieldcatalog               = i_field</b>
     IT_SORT                       =
     IT_FILTER                     =
  EXCEPTIONS
    invalid_parameter_combination = 1
    program_error                 = 2
    too_many_lines                = 3
    OTHERS                        = 4
<b>4</b>.
You should remove
<b>i_structure_name = 'JOINTAB'</b>
y should use this when u pass single table data display.
I hope that it helps u .
<b>Thanks,
Venkat.O</b>