Set Listbox Values At Selection Screen

When you hit F8 , the p_par will have the key fields value of selected list item.

*** Type Pool
type-pools : vrm.
.
.
*** Her's the definition of listbox parameter
parameters : p_par type mara-mtart as listbox visible length 15.
.
.

*** Event Block
at selection-screen output.
  perform at_sel_output.

.
.
.

*&---------------------------------------------------------------------*
*&      Form  at_sel_output
*&---------------------------------------------------------------------*
form at_sel_output.

  data : lt_list  type vrm_values with header line .

  lt_list-key = 'K1'.
  lt_list-text = ' First One'.
  append lt_list.
  lt_list-key = 'K2'.
  lt_list-text = ' Second One'.
  append lt_list.
  lt_list-key = 'K3'.
  lt_list-text = ' Third One'.
  append lt_list.

  call function 'VRM_SET_VALUES'
    exporting
      id              = 'P_PAR'
      values          = lt_list[]
    exceptions
      id_illegal_name = 1
      others          = 2.

endform.                    "at_sel_output