采购订单增强

想写个增强，在创建采购订单的时候自动根据一定规则将利润中心维护进去，试了好几个增强都写不进去，请高手指教，我找的增强
都是读数据的不能回写。

用IF_EX_ME_PROCESS_PO_CUST里面的Process_Item实现. 类似增强在出口中无法实现,必强要在BADI中做.

e.g.

"e+ Enhancement Added By Michael Chow 2008.06.18
" When EKPO-KNTTP EQ 'Y' and Material Type EQ ' UNBW '
"THEN Set item to FOC automacticaly

If ls_mepoitem-KNTTP EQ 'Y'.
   CLEAR l_mara.
   SELECT SINGLE * FROM MARA  into L_MARA
     WHERE MATNR = ls_mepoitem-MATNR
     and MTART = 'UNBW'.
     IF SY-SUBRC EQ 0.
ls_mepoitem-WEUNB  = ''.
ls_mepoitem-WEBRE  = ''..
CALL METHOD im_item->Set_DATA EXPORTING  IM_DATA = ls_mepoitem.
ENDIF.
ENDIF.


"End of adding

thank you