1. Why dynamic selection screens?

A report with many options gets crowded. If a user only wants order headers, why show filters for items? A dynamic selection screen shows only the fields that matter for the choice the user just made.

• Cleaner screen, fewer mistakes
• One report can serve several purposes
• Hidden fields cannot filter the data by accident

The tools are three: a trigger (checkbox or radio button), a group (MODIF ID), and a loop (LOOP AT SCREEN).

2. Checkboxes as mode selectors

A normal checkbox does not talk to the program when clicked. To make the screen react, add USER-COMMAND.

PARAMETERS: p_hdr AS CHECKBOX USER-COMMAND uc1 DEFAULT 'X',
           p_itm AS CHECKBOX USER-COMMAND uc2.

Radio buttons work the same way: RADIOBUTTON GROUP g1 USER-COMMAND uc on the first button of the group. Use radio buttons when only one mode may be active. Use checkboxes when several can be on together, as in this blog.

3. MODIF ID: grouping fields

MODIF ID puts a field into a named group. Later, one loop can show or hide the whole group.

SELECT-OPTIONS s_erdat FOR gv_erdat MODIF ID hdr.
SELECT-OPTIONS s_matnr FOR gv_matnr MODIF ID itm.
PARAMETERS     p_qty   TYPE vbap-kwmeng MODIF ID itm.

• The group name has at most 3 characters, and is written in capitals in the loop.
• It covers the input boxes and the label next to them.
• For a select-option it covers both the From and To boxes.

4. AT SELECTION-SCREEN OUTPUT: the magic event

This event runs every time the selection screen is about to be shown: the first time, and after every click that triggers a user command. It is the right place to change how fields look.

5. LOOP AT SCREEN: iterating screen fields

SCREEN is a built-in table that describes every element on the screen. Loop over it, check the group, change the attributes, and save with MODIFY SCREEN.

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    IF screen-group1 = 'ITM'.
      IF p_itm = abap_true.
        screen-active = 1.
      ELSE.
        screen-active = 0.
      ENDIF.
      MODIFY SCREEN.
    ENDIF.
  ENDLOOP.

6. SCREEN-ACTIVE vs. SCREEN-INPUT

7. Clearing hidden values

A hidden field still holds its old value. If the user typed a material, then un-ticked the item option, the material would still be in memory. Clear hidden filters so they cannot affect anything.

IF p_itm = abap_false.
  CLEAR: s_matnr[], p_qty.
ENDIF.

For a select-option, clear the table body with s_matnr[]. The trade-off: when the user ticks the box again, the fields start empty.

8. Program 3: full code

REPORT zdynamic_screen.

DATA: gv_erdat TYPE vbak-erdat,
      gv_auart TYPE vbak-auart,
      gv_matnr TYPE vbap-matnr.

*---------------------------------------------------------------------*
* Selection screen
*---------------------------------------------------------------------*
SELECTION-SCREEN BEGIN OF BLOCK b1 WITH FRAME TITLE TEXT-001.
  PARAMETERS: p_hdr AS CHECKBOX USER-COMMAND uc1 DEFAULT 'X',
             p_itm AS CHECKBOX USER-COMMAND uc2.
SELECTION-SCREEN END OF BLOCK b1.

SELECTION-SCREEN BEGIN OF BLOCK b2 WITH FRAME TITLE TEXT-002.
  SELECT-OPTIONS: s_erdat FOR gv_erdat MODIF ID hdr,
                  s_auart FOR gv_auart MODIF ID hdr,
                  s_matnr FOR gv_matnr MODIF ID itm.
  PARAMETERS: p_qty TYPE vbap-kwmeng MODIF ID itm.
SELECTION-SCREEN END OF BLOCK b2.

*---------------------------------------------------------------------*
* Events
*---------------------------------------------------------------------*
INITIALIZATION.
  s_erdat-sign   = 'I'.
  s_erdat-option = 'BT'.
  s_erdat-low    = sy-datum - 30.
  s_erdat-high   = sy-datum.
  APPEND s_erdat.

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    CASE screen-group1.
      WHEN 'HDR'.
        screen-active = COND #( WHEN p_hdr = abap_true THEN 1 ELSE 0 ).
        MODIFY SCREEN.
      WHEN 'ITM'.
        screen-active = COND #( WHEN p_itm = abap_true THEN 1 ELSE 0 ).
        MODIFY SCREEN.
    ENDCASE.
  ENDLOOP.

  " Clear filters of hidden groups
  IF p_hdr = abap_false.
    CLEAR: s_erdat[], s_auart[].
  ENDIF.
  IF p_itm = abap_false.
    CLEAR: s_matnr[], p_qty.
  ENDIF.

AT SELECTION-SCREEN.
  " Validate only when the user executes (F8), not when ticking boxes
  IF sy-ucomm = 'ONLI' AND p_hdr = abap_false AND p_itm = abap_false.
    MESSAGE 'Select at least one report type' TYPE 'E'.
  ENDIF.

START-OF-SELECTION.
  IF p_hdr = abap_true.
    PERFORM show_headers.
  ENDIF.
  IF p_itm = abap_true.
    PERFORM show_items.
  ENDIF.

*---------------------------------------------------------------------*
* FORM show_headers: order headers (VBAK)
*---------------------------------------------------------------------*
FORM show_headers.
  SELECT vbeln, erdat, auart, netwr, waerk
    FROM vbak
    WHERE erdat IN @s_erdat
      AND auart IN @s_auart
    ORDER BY erdat DESCENDING, vbeln
    INTO TABLE @DATA(lt_headers)
    UP TO 200 ROWS.

  WRITE: / 'ORDER HEADERS'.
  ULINE.
  IF sy-subrc <> 0.
    WRITE: / 'No order headers found'.
    RETURN.
  ENDIF.

  LOOP AT lt_headers INTO DATA(ls_header).
    WRITE: / ls_header-vbeln, ls_header-erdat, ls_header-auart,
             ls_header-netwr, ls_header-waerk.
  ENDLOOP.
  SKIP.
ENDFORM.

*---------------------------------------------------------------------*
* FORM show_items: order items (VBAP)
*---------------------------------------------------------------------*
FORM show_items.
  SELECT vbeln, posnr, matnr, kwmeng, netwr, waerk
    FROM vbap
    WHERE matnr IN @s_matnr
      AND kwmeng >= @p_qty
    INTO TABLE @DATA(lt_items)
    UP TO 200 ROWS.

  WRITE: / 'ORDER ITEMS'.
  ULINE.
  IF sy-subrc <> 0.
    WRITE: / 'No order items found'.
    RETURN.
  ENDIF.

  LOOP AT lt_items INTO DATA(ls_item).
    WRITE: / ls_item-vbeln, ls_item-posnr, ls_item-matnr,
             ls_item-kwmeng, ls_item-netwr, ls_item-waerk.
  ENDLOOP.
ENDFORM.

9. Walkthrough

What the user sees

Remember to set selection texts for each field, as in Blog 2, so users see clear labels.

10. Try it yourself

• Replace the checkboxes with radio buttons so only one mode can be on.
• Make s_matnr grey (screen-input = 0) instead of hidden.
• Add a third group CST for customer filters (KUNNR) with its own checkbox.
• Use screen-required = 1 to make the date range mandatory only when headers are selected.
• Replace the WRITE output with the ALV from Blog 5 or 6.

11. Common mistakes

• No USER-COMMAND on the checkbox. The screen does not refresh when clicked.
• Forgetting MODIFY SCREEN. Changes to screen- fields are ignored.
• Group name in lowercase or longer than 3 characters. The group never matches.
• Putting the logic in AT SELECTION-SCREEN instead of AT SELECTION-SCREEN OUTPUT. Hiding must be set before the screen is drawn.
• Error message without a sy-ucomm check. The user cannot even click the checkboxes.
• Database access inside AT SELECTION-SCREEN OUTPUT. It runs on every click and makes the screen slow.
• Hidden fields with OBLIGATORY. The user cannot run the report. Use screen-required.
• Forgetting to clear hidden filters, so old values silently filter the data.