Selection screen processing in Module pool

Question

Dear Friends,
I am preparing a module pool, in which from one screen, i have to call a selection screen. I want to define this selection screen in the same program. Under which event block, i can define this selection screen?
Once its called, how can i process the selection screen ( like START-OF-SELECTION etc ?). If i use a LEAVE TO LIST-PROCESSING to display some output, how can i process the user actions in this list?
Thanking you in anticipation.
Deepak

Answer 1

HI Max,
Thanks a lot for your reply. It was really helpfull. But my problem is not yet solved.
When i call the selection screen from the PBO of a screen, the selection screen is not being displayed. Only the blank screen is displayed. So i tried another way. I put the CALL SELECTION-ECREEN  statement in the USER_COMMAN_100 module of PAI of the previous screen. (ie when user choose a button from the tool bar, in the initial screen the selection screen will be displayed.)
module user_command_0100 input.
  OK_SAVE = OK100.
  CLEAR OK100.
  CASE OK_SAVE.
    WHEN 'LIST'.
      CALL SELECTION-SCREEN 200.
      IF SY-SUBRC = 0.
        PERFORM PROCESS_LIST.
      ELSE.
        leave screen.
      ENDIF.
endmodule.                 " USER_COMMAND_0100  INPUT
form process_list.
... reading database...
IF SY-SUBRC = 0.
  LEAVE TO LIST-PROCESSING AND RETURN TO SCREEN 100.
  SET PF-STATUS 'GUI_LIST'.
    LOOP AT ITAB.
      WRITE :/ ITAB-BUKRS, ITAB-BELNR, ITAB-GJAHR.
    ENDLOOP.
  LEAVE SCREEN.
  ENDIF.
endform.                    " PROCESS_LIST
Now i have two problems to solve.
1. I want to come back to the same selection screen (screen no 200) instead of screen 100, when the user click 'back' button in the list. but if i specify screen no 200 in
LEAVE TO LIST-PROCESSING AND RETURN TO SCREEN 100.
it gives runtime error. ( Msg: Selection screen ZTEST3 0200 was not called using CALL SELECTION-SCREEN). How to return back to selection screen?
and
2. If the user selects a line from the list(PICK/F2), that value has to be passed to the input field of first screen( ie the initial screen from where i called the selection screen : screen no 100) For this, where can i write the code to process the user actions in the list?
Thanking you in anticipation
Deepak