Problem in Populating a listbox

Question

hello everyone,
In my report prog, there are two parameters:
p_matno LIKE mara-matnr OBLIGATORY,
p_s_loc TYPE mard-lgort AS LISTBOX VISIBLE LENGTH 8.
When I input p_matno and press enter, the listbox P_S_LOC is populated with the corresponding values by triggering followingselect query:
SELECT lgort FROM mard INTO CORRESPONDING FIELDS OF TABLE it_storeloc WHERE matnr = p_matno AND werks = '1501'.
This works fine .. But now the condition is, if I dont select any value populated in the listbox and execute the prog(press F8), it should give an error msg ..
I wrote that piece of code as this in the STARTt-OF-SELECTION
IF P_S_LOC is INITIAL.
    message 'Storage Location Needs to be Entered.' type 'S'.
ENDIF:
but when the error message is generated, the values in the listbox go away and it becomes empty .. How can i retain this values in the listbox ??
Kindly help .. any input will be apprecitaed ..

Answer 1

Hey Venkat,
Here is the code:Do check out the comments beside every line for better understanding.
*---------for drop down list --------------------*
TYPE-POOLS: vrm.
DATA: it_val TYPE vrm_values,
      w_line LIKE LINE OF it_val,
      it_storeloc TYPE TABLE OF mard,
      w_storeloc LIKE LINE OF it_storeloc,
      v_name TYPE vrm_id VALUE 'P_S_LOC'.
// List of Parameters
PARAMETERS :  p_matno LIKE mara-matnr OBLIGATORY,
              p_werks LIKE marc-werks OBLIGATORY DEFAULT '1501',
              p_s_loc TYPE mard-lgort AS LISTBOX VISIBLE LENGTH 8,
              p_erdat TYPE vbap-erdat,
              p_netwr TYPE lips-netwr,
              p_qty TYPE i.
AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.  "Only Material Number is to be inputted. Other ields will be populated on the basis of material number.
    IF screen-name = 'P_ERDAT' OR screen-name = 'P_NETWR' OR screen-name = 'P_QTY'.
       screen-input = 0.
    ENDIF.
    MODIFY SCREEN.
  ENDLOOP.
AT SELECTION-SCREEN.
*  CLEAR : p_erdat,p_netwr,p_qty.
  PERFORM matnr_validation. "Validation of Material Number
  PERFORM fetch_mat_description. "Getting material description
  PERFORM fetch_data. "fetching data - here I have called the FM to populate the listbox
  PERFORM fetch_mrp_value. "Fetching MRP value nad putting it on the p_netwr
START-OF-SELECTION.
  PERFORM call_smartform. "here I'm calling the smartform
FORM fetch_data .
SELECT lgort FROM mard INTO CORRESPONDING FIELDS OF TABLE it_storeloc WHERE matnr = p_matno AND werks = '1501'.
  LOOP AT it_storeloc INTO w_storeloc.
    w_line-key = w_storeloc-lgort.
    APPEND w_line TO it_val.
  ENDLOOP.
  CALL FUNCTION 'VRM_SET_VALUES'
    EXPORTING
      id                    = v_name
      values                = it_val
  p_erdat = sy-datum.
  clear: it_val.
ENDFORM.                    " FETCH_DATA
FORM Call_smartform
IF P_S_LOC is INITIAL.
*MESSAGE s000(zwm_msg) with 'Storage Location Needs to be Entered.'.
    message 'Storage Location is missing : Enter the material again and choose the storage location.' type 'S'.
ELSE.
  output_options-tdcopies = p_labels.
  CALL FUNCTION 'SSF_FUNCTION_MODULE_NAME'
    EXPORTING
      formname           = v_layout
    IMPORTING
      fm_name            = v_form_name
    EXCEPTIONS
      no_form            = 1
      no_function_module = 2
      OTHERS             = 3.
  IF sy-subrc <> 0.
    MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
       WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
  ENDIF.
  CALL FUNCTION v_form_name
    EXPORTING
      control_parameters = control_parameters
      output_options     = output_options
            p_exp            = p_exp
    EXCEPTIONS
      formatting_error = 1
      internal_error   = 2
      send_error       = 3
      user_canceled    = 4
      OTHERS           = 5.
  IF sy-subrc <> 0.
    MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
             WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
  ENDIF.
ENDIF.
ENDFORM.                    "
Edited by: sohamshah on Sep 30, 2009 12:00 PM