Validation required on CELL in ALV using OOPs

Hi all,

I am using class CL_GUI_ALV_GRID to show the data in ALV.

In ALV on editable field is there to enter EBELN.

When i enter any value in that field and press 'ENTER', it shold fetch the LIFNR from EKKO and shows that in very next field in ALV.

Please tell me in which EVENT of CL_GUI_ALV_GRID should i write the code??

remember, i want this logic while i press ENTER or AFTER SELECTING FROM F4 DROP DOWN...

Thnaks,,,