this is the source code to build the fieldcat
FORM display_data . PERFORM build_fieldcat. gs_layout-cwidth_opt = ‘X’. gs_layout-stylefname = ‘CELLTAB’. gs_layout-info_fname = ‘LINECOLOR’. CALL FUNCTION ‘REUSE_ALV_GRID_DISPLAY_LVC’ EXPORTING i_callback_program = sy-repid i_callback_pf_status_set = ‘SET_PF_STATUS’ i_callback_user_command = ‘HANDLE_USER_COMMAND’ I_CALLBACK_HTML_TOP_OF_PAGE = ‘HTML_TOP_OF_PAGE’ is_layout_lvc = gs_layout it_fieldcat_lvc = gt_fieldcat TABLES t_outtab = gt_result_show EXCEPTIONS inconsistent_interface = 1 program_error = 2. ENDFORM.
this is the code to handle user command