如何给屏幕字段（下拉框和输入框）用代码添加F4 search help

有些时候我们可能要对屏幕上一些字段用代码写实现search help功能
下面用一个简单例子演示：

*&----------------------------------------------------------------*
*& Report ztest_pillar *
*&----------------------------------------------------------------*

report ztest_pillar.

* Global Data

TYPES: BEGIN OF type_carrid,
carrid TYPE spfli-carrid,
carrname TYPE scarr-carrname,
END OF type_carrid.

DATA itab_carrid TYPE STANDARD TABLE OF type_carrid.

* Selection Screen

parameters airline(2) type c.

*&---------------------------------------------------------------------*
*& Processing Blocks called by the Runtime Environment *
*&---------------------------------------------------------------------*

* Event Block AT SELECTION-SCREEN ON VALUE-REQUEST FOR

at selection-screen on value-request for airline.
perform frm_f4_help.

* Form for generating F4 HELP for parameter AIRLINE

form FRM_F4_HELP .
SELECT carrid carrname
FROM scarr
INTO CORRESPONDING FIELDS OF TABLE itab_carrid.

CALL FUNCTION 'F4IF_INT_TABLE_VALUE_REQUEST'
EXPORTING
retfield = 'CARRID' "指定要返回屏幕参数的在内表中的field
value_org = 'S' "S代表structure
dynpprog = sy-repid "指定屏幕参数所在的程序名称
dynpnr = sy-dynnr "指定参数所在的屏幕编号
dynprofield = 'AIRLINE'"指定屏幕参数的名称
TABLES
value_tab = itab_carrid "内表
EXCEPTIONS
parameter_error = 1
no_values_found = 2
OTHERS = 3.
IF sy-subrc <> 0.
...
ENDIF.
endform. " FRM_F4_HELP