How valid input after changed selecting from search help?

Hi

I have a

PARAMETERS: p_ABKRS TYPE PA0001-ABKRS OBLIGATORY.

Value to parameter p_ABKRS I can set by write or select from search help (F4).

When I set value p_ABKRS by write, I can catch event AT SELECTION-SCREEN OUTPUT.

But how can I catch event when changing value using search help (F4)?

I need catch both event changing by write and search help.

Thank you