procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
  WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
var
  LCB: TDBLookupComboBox;
begin
  if ActiveControl is TDBLookupComboBox then
  begin
    LCB := ActiveControl as TDBLookupComboBox;

    // هل القائمة مفتوحة؟
    if SendMessage(LCB.Handle, CB_GETDROPPEDSTATE, 0, 0) <> 0 then
    begin
      if WheelDelta > 0 then
        LCB.Perform(WM_KEYDOWN, VK_UP, 0)
      else
        LCB.Perform(WM_KEYDOWN, VK_DOWN, 0);

      Handled := True;
    end;
  end;
end;