三、处理说明

    1、程序首先执行INITIALIZATION 事件；

    2、接着执行AT SELECTION SCREEN OUTPUT事件(也就是PBO) ，在这个事件里你可以通过修改系统默认screen内表修改屏幕的某些属性；
    PARAMETERS: TEST1(10) MODIF ID SC1,
                TEST2(10) MODIF ID SC2,
                TEST3(10) MODIF ID SC1,
                TEST4(10) MODIF ID SC2.
    AT SELECTION-SCREEN OUTPUT.
    LOOP AT SCREEN.
      IF SCREEN-GROUP1 = 'SC1'.
        SCREEN-INTENSIFIED = '1'.
        MODIFY SCREEN.
        CONTINUE.
      ENDIF.
      IF SCREEN-GROUP1 = 'SC2'.
        SCREEN-INTENSIFIED = '0'.
        MODIFY SCREEN.
      ENDIF.
    ENDLOOP.

    3、系统将屏幕输出到用户端，用户就可进行交互操作了。也就是PAI处理，其分为

    3.1字段AT SELECTION-SCREEN ON XXXX.

    REPORT EVENT_DEMO.
    NODES SPFLI.
    AT SELECTION-SCREEN ON CITY_FR.
      IF CARRID-LOW EQ 'AA' AND CITY_FR NE 'NEW YORK'.
        MESSAGE E010(HB).
      ENDIF.

    3.2区域AT SELECTION-SCREEN ON BLOCK  XXXX.

    REPORT EVENT_DEMO.
    SELECTION-SCREEN BEGIN OF BLOCK PART1 WITH FRAME.
      PARAMETERS: NUMBER1 TYPE I,
                  NUMBER2 TYPE I,
                  NUMBER3 TYPE I.
    SELECTION-SCREEN END OF BLOCK PART1.

    SELECTION-SCREEN BEGIN OF BLOCK PART2 WITH FRAME.
      PARAMETERS: NUMBER4 TYPE I,
                  NUMBER5 TYPE I,
                  NUMBER6 TYPE I.
    SELECTION-SCREEN END OF BLOCK PART2.

    AT SELECTION-SCREEN ON BLOCK PART1.
      IF NUMBER3 LT NUMBER2 OR
         NUMBER3 LT NUMBER1 OR
         NUMBER2 LT NUMBER1.
         MESSAGE E020(HB).
      ENDIF.

    AT SELECTION-SCREEN ON BLOCK PART2.
      IF NUMBER6 LT NUMBER5 OR
         NUMBER6 LT NUMBER4 OR
         NUMBER5 LT NUMBER4.
         MESSAGE E030(HB).
      ENDIF.

    3.3屏幕AT SELECTION-SCREEN

    在此事件里可以进行对用户输入进行完整性进行检查。
    在PAI处理中出现错误，系统返回屏幕，请求用户重新输入；

    4、当所有的PAI执行后，则进入START-OF-SELECTION事件的执行。