怎样在选择屏幕中添加LISTBOX

TYPE-POOLS: vrm.
DATA: itb_list TYPE vrm_values.
DATA: wa LIKE LINE OF itb_list.
PARAMETERS: listbox LIKE mara-matnr AS LISTBOX VISIBLE LENGTH 20.

INITIALIZATION.
  wa-key = '01'.
  wa-text = '文本1'.
  APPEND  wa TO itb_list.
  wa-key = '02'.
  wa-text = '文本2'.
  APPEND  wa TO itb_list.
  wa-key = '03'.
  wa-text = '文本3'.
  APPEND  wa TO itb_list.

AT SELECTION-SCREEN OUTPUT.
  CALL FUNCTION 'VRM_SET_VALUES'
    EXPORTING
      id     = 'LISTBOX'
      values = itb_list.

END-OF-SELECTION.
  WRITE: /  listbox.