HI,
FORM user_command USING v_comm TYPE sy-ucomm
wa_selfield TYPE slis_selfield.
"layout
CASE v_comm.
WHEN '&CHK'. "Your Function code for Select allbutton
wa_selfield-refresh = 'X'.
LOOP AT it_dummy INTO wa_dummy. "it_dummy is internal table or final table.
wa_dummy-chk = 'X'.
MODIFY it_dummy FROM wa_dummy TRANSPORTING chk.
CLEAR wa_dummy.
ENDLOOP.
endform.
This will mark all checkbox in the alv grid selected.
Re gards,
Ravi Pratap Singh