Keep previous values for Select-Options

Question

I am using macros to populate my selections with the previously entered values.  Everything works fine until I want to delete the previous selections for so_snp via the Trash Can button.  The selections come back.  The issue seems to be that the selections are deleted from the so_snp range but then the AT SELECTION-SCREEN OUTPUT executes makro_get_range which re-populates the so_snp selection from the data stored in the buffer because so_snp is initial.  How do I get the AT SELECTION-SCREEN code to execute first so that the makro_set_range can clear out the shared buffer for '/SAPAPO/PT_PLAN_SNP'.  I have included excerpts from my ABAP program.
Any help would be appreciated.  I struggled with this all day long.
Best regards,
Sandy
DEFINE makro_get_range.
initialization
  clear:
    lv_line,
    lv_key.
import SET/GET-parameter from shared buffer
  if &2[] is initial.
    concatenate sy-uname  &1 '_T' into lv_key.          
    import &2[] from shared buffer indx(st) id lv_key.
    if sy-subrc eq 0.
      read table &2 index 1.
    endif.
  endif.
  if &2 is initial.
    get parameter id &1 field &2.
    if sy-subrc ne 0 and &2 is initial.
      refresh &2[].
    endif.
    if not &2   is initial
       and &2[] is initial.
      append &2.
    endif.
  endif.
END-OF-DEFINITION.
DEFINE makro_set_range.
initialization
  clear:
    lv_line,
    lv_key.
  concatenate sy-uname &1 '_T' into lv_key.
export SET/GET-parameter to shared buffer
  describe table &2[] lines lv_line.
  if lv_line gt 1.
    export &2[] to shared buffer indx(st) id lv_key.
  else.
    delete from shared buffer indx(st) id lv_key.
    set parameter id &1 field &2.
  endif.
END-OF-DEFINITION.
SELECT-OPTIONS so_snp FOR /sapapo/matloc-planner_snp.
AT SELECTION-SCREEN OUTPUT.
   makro_get_range '/SAPAPO/PT_PLAN_SNP'    so_snp.
AT SELECTION-SCREEN.
    makro_set_range '/SAPAPO/PT_PLAN_SNP'    so_snp.

Answer 1

Can you set a flag to indicate that it needs to be done only once like below?
AT SELECTION-SCREEN OUTPUT.
IF v_flag_get_done_once IS INITIAL.
*-- get the values from the shared buffer
  makro_get_range '/SAPAPO/PT_PLAN_SNP' so_snp.
  v_flag_get_done_once = 'X'.
ELSE.
*-- user manipulated the selection screen values, so
*   don't do it again. Do Nothing.
ENDIF.
Srinivas