如下代码将会输出一个P_U的字段

PARAMETERS p_u TYPE string VISIBLE LENGTH 12 MEMORY ID m1.

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    IF screen-name = 'P_U'.
      screen-invisible = '1'.
      MODIFY SCREEN.
    ENDIF.
  ENDLOOP.

如果我们给这个字段设置一个默认值，参考如下代码，这时将会输出什么呢？

DATA: lv_xs TYPE xstring.

PARAMETERS p_u TYPE string VISIBLE LENGTH 12 MEMORY ID m1.

INITIALIZATION.
  lv_xs =  '0000'.
  p_u = cl_bcs_convert=>xstring_to_string( iv_cp = '4103' iv_xstr = lv_xs ).

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    IF screen-name = 'P_U'.
      screen-invisible = '1'.
      MODIFY SCREEN.
    ENDIF.
  ENDLOOP.

会发现输入框消失了

 此时将代码修改到上一个版本，并在AT SELECTION-SCREEN OUTPUT下清除该值，仍然没有输入框

DATA: lv_xs TYPE xstring.

PARAMETERS p_u TYPE string VISIBLE LENGTH 12 MEMORY ID m1.

AT SELECTION-SCREEN OUTPUT.
  LOOP AT SCREEN.
    IF screen-name = 'P_U'.
      screen-invisible = '1'.
      MODIFY SCREEN.
    ENDIF.
  ENDLOOP.
  CLEAR: p_u.

START-OF-SELECTION.
  WRITE:/ p_u.

SAPKB74024    SAP Basis Component