How to capture the user change in an input field on a selection screen?

Question

I am coding a selection screen in which there are two input fields. The first field takes a Unix directory from the user input. Based on the input value, the second field will be populated with a the name of a file under the corresponding directory.
My question is how I can make the program capture the user input without having to make the user press ENTER after they enter the value in the first field?
Any help will be greatly appreciated.

Answer 1

Venkat,
Actually you led me to the real solution! It's the function module DYNP_VALUES_READ that does the trick for me. This function enables the program to capture dynamic user changes without recourse to PAI. Please refer to the code below:
REPORT   zreiabsintf MESSAGE-ID zreiabsintfmc.
*<HGDC------------------------------------------------------------------
*  Selection screen for the conversion program
*HGDC>------------------------------------------------------------------
SELECTION-SCREEN BEGIN OF BLOCK input WITH FRAME TITLE text-001.
PARAMETERS: p_indir   LIKE epsf-epsdirnam OBLIGATORY,                   " Inbound file directory
            p_infile  LIKE epsf-epsfilnam DEFAULT gc_infile OBLIGATORY, " Inbound file name
SELECTION-SCREEN END OF BLOCK input.
*<HGDC------------------------------------------------------------------
*   Displays a file-open dialog when the user clicks the search
*   help button next to the inbound file text field. The user
*   can select the inbound file visually.
*HGDC>------------------------------------------------------------------
AT SELECTION-SCREEN ON VALUE-REQUEST FOR p_infile.
* Capture any user change to the directory.
  PERFORM check_dir_change.
* Display the file open dialog
  PERFORM file_open_dialog CHANGING p_infile.
*<HGDC------------------------------------------------------------------
* Global constants
*HGDC>------------------------------------------------------------------
CONSTANTS:
    gc_indir  LIKE epsf-epsdirnam
              VALUE '/interfaces/<SID>/inbound/',      " Default inbound directory template
    gc_infile LIKE epsf-epsfilnam VALUE 'input'.       " Default inbound file name
*<HGDC------------------------------------------------------------------
* Global data
*HGDC>------------------------------------------------------------------
DATA:
    gs_dynpfields   TYPE dynpread,                        " Fields of the current screen
     gt_dynpfields   LIKE STANDARD TABLE OF gs_dynpfields. " Table of the screen fields
*&      Form  file_open_dialog
*       Opens a dialog window for the user to choose a file in
*       the specified Unix directory.
*      <--P_FILE is the file to be selected.
FORM file_open_dialog  CHANGING p_file.
* Validate the directory.
  OPEN DATASET p_indir FOR INPUT IN BINARY MODE.
  IF sy-subrc NE 0.
    MESSAGE i001(zreiabsintfmc) WITH p_indir.    " Unable to open the given directory
    EXIT.
  ENDIF.
  CLOSE DATASET p_indir.
* Call the dialog window to open a file in the directory.
  CALL FUNCTION '/SAPDMC/LSM_F4_SERVER_FILE'
    EXPORTING
      directory        = p_indir
    IMPORTING
      serverfile       = p_file
    EXCEPTIONS
      canceled_by_user = 1
      OTHERS           = 2.
  IF sy-subrc NE 0.
    MESSAGE i002(zreiabsintfmc).                 " Failed to open the file.
    EXIT.
  ENDIF.
ENDFORM.                    " file_open_dialog
*&      Form  check_dir_change
*       text
*  -->  p1        text
*  <--  p2        text
FORM check_dir_change .
  CLEAR gs_dynpfields.
  CLEAR gt_dynpfields.
  gs_dynpfields-fieldname = 'P_INDIR'.
  gs_dynpfields-fieldvalue = p_indir.
  APPEND gs_dynpfields TO gt_dynpfields.
  CALL FUNCTION 'DYNP_VALUES_READ'
    EXPORTING
      dyname               = sy-repid
      dynumb               = sy-dynnr
    TABLES
      dynpfields           = gt_dynpfields
    EXCEPTIONS
      invalid_abapworkarea = 1
      invalid_dynprofield  = 2
      invalid_dynproname   = 3
      invalid_dynpronummer = 4
      invalid_request      = 5
      no_fielddescription  = 6
      invalid_parameter    = 7
      undefind_error       = 8
      double_conversion    = 9
      stepl_not_found      = 10
      OTHERS               = 11.
  IF sy-subrc  NE 0.
* MESSAGE ID SY-MSGID TYPE SY-MSGTY NUMBER SY-MSGNO
*         WITH SY-MSGV1 SY-MSGV2 SY-MSGV3 SY-MSGV4.
  ENDIF.
  READ TABLE gt_dynpfields INTO gs_dynpfields INDEX 1.
  p_indir = gs_dynpfields-fieldvalue.
ENDFORM.                    " check_dir_change
Thanks for all your answers! The problem is now solved.
Edited by: Ning Hu on Apr 9, 2008 11:32 AM
Edited by: Ning Hu on Apr 9, 2008 11:34 AM