ABAP--如何使选择屏幕的初始化事件再次触发

最近一个同事有一个比较变态的用户需求,他希望每次回到选择屏幕时，选择参数是有程序控制输入的，用户客户端的输入清除。对此需求有两种处理方法：
一、在AT SELECTION-SCREEN中写赋值语句，这种方法你可能需要中间变量缓存选择条件用于查询，代码样例：
REPORT demo_write_statement.
tables vbak.
DATA:  NAME(20) VALUE 'SOURCE',
      SOURCE(10) VALUE 'abcd',
      TARGET(10).

select-options k_kunnr for vbak-kunnr.

data: is_parent  type i value 0.

INITIALIZATION.
×  refresh k_kunnr.
AT SELECTION-SCREEN.
  refresh k_kunnr.
  MOVE: 'I'      TO k_kunnr-SIGN,
        'EQ'     TO k_kunnr-OPTION,
        '9999'   TO k_kunnr-LOW.
  APPEND k_kunnr.
*SYSTEM-CALL INITIALIZATION.

二、在Initialization事件中写赋值代码
 在Initialization事件中写赋值代码，默认情况只有第一次会影响输入屏幕，以后将失去作用。为了使该代码起作用你必须在选择屏幕的其他事件中执行SYSTEM-CALL INITIALIZATION.这个语句。代码样例：
REPORT demo_write_statement.
tables: spfli.
DATA: tab_spfli   TYPE TABLE OF spfli,
      tab_sflight TYPE SORTED TABLE OF sflight
                       WITH UNIQUE KEY table_line,
      wa LIKE LINE OF tab_sflight.
select-options s_CARRID for spfli-CARRID.

INITIALIZATION.
  refresh s_CARRID.
  MOVE: 'I'      TO s_CARRID-SIGN,
        'EQ'     TO s_CARRID-OPTION,
        'AZ'   TO s_CARRID-LOW.
  APPEND k_kunnr.

AT SELECTION-SCREEN.
start-of-SELECTION.
  SELECT carrid connid
  INTO   CORRESPONDING FIELDS OF TABLE tab_spfli
  FROM   spfli
  WHERE  CARRID in s_CARRID .

  SYSTEM-CALL INITIALIZATION.
  SELECT  carrid connid fldate
    INTO  CORRESPONDING FIELDS OF TABLE tab_sflight
    FROM  sflight
    FOR ALL ENTRIES IN tab_spfli
    WHERE carrid = tab_spfli-carrid AND
          connid = tab_spfli-connid.

  LOOP AT tab_sflight INTO wa.

    AT NEW connid.
      WRITE: / wa-carrid, wa-connid.
    ENDAT.

    WRITE: / wa-fldate.

  ENDLOOP.

相关连接：http://blog.youkuaiyun.com/CompassButton/archive/2006/08/18/1091626.aspx