Custom container alv sap abap

REPORT  YJ_OOPS_ALV_CUSTOMER_CONTAINER.
DATA : o_cust TYPE REF TO cl_gui_custom_container,
        o_alv TYPE REF TO cl_gui_alv_grid,
        it_mara TYPE TABLE OF mara,
        wa_mara TYPE mara,
        ok_code TYPE sy-ucomm.
PARAMETERS  : p_matnr like mara-matnr.
START-OF-SELECTION.
   PERFORM data_fetch.
   CALL SCREEN 100.

FORM data_fetch .
   SELECT * FROM mara INTO TABLE it_mara WHERE matnr = p_matnr.
 ENDFORM.                    " DATA_FETCH


MODULE status_0100 OUTPUT.
   SET PF-STATUS 'STATUS'.
   SET TITLEBAR 'TITLE'.
ENDMODULE.                 " STATUS_0100  OUTPUT


MODULE user_command_0100 INPUT.
   CASE ok_code.
     WHEN 'BACK'  .
       LEAVE TO SCREEN 0.
     WHEN 'EXIT'.
       LEAVE PROGRAM.
   ENDCASE.
 ENDMODULE.                 " USER_COMMAND_0100  INPUT


MODULE display_alv OUTPUT.
  CREATE OBJECT o_cust
     EXPORTING
       container_name              = 'CUSTOM'.
    CREATE OBJECT o_alv
       EXPORTING
         i_parent          = O_CUST.
CALL METHOD o_alv->set_table_for_first_display
   EXPORTING
     i_structure_name              = 'MARA'
   CHANGING
     it_outtab                     = IT_mara.
ENDMODULE.                 " DISPLAY_ALV  OUTPUT