Hello HashMukh,
You are calling FM in wrong place, change FM with in the start-of-selection, PF below Example.
AT SELECTION-SCREENONVALUE-REQUEST FOR p_infile.
CALLFUNCTION'F4_FILENAME'
EXPORTING
program_name = syst-cprog
dynpro_number = syst-dynnr
field_name = 'p_infile'
IMPORTING
file_name = p_infile.
START-OF-SELECTION.
PERFORM upload_file.
PERFORM process_order_data.
*&---------------------------------------------------------------------*
*& Form upload_file
*&---------------------------------------------------------------------*
* text
*----------------------------------------------------------------------*
FORM upload_file.
CALLFUNCTION'AA_FILE_UPLOAD_EXCEL'
EXPORTING
i_filename = p_infile
* I_TEST =
* I_UCOMM =
* I_MAXCOLS =
i_delimiter = ','
TABLES
et_filecontent = itab
EXCEPTIONS
error_accessing_file = 1
OTHERS = 2
.
IF sy-subrc <> 0.
MESSAGEID sy-msgid TYPE sy-msgty NUMBER sy-msgno
WITH sy-msgv1 sy-msgv2 sy-msgv3
Regards
KMC