ScrollBox 响应鼠标滚轮和ComboBox禁止滚动

procedure TForm1.FormMouseWheel(Sender: TObject; Shift: TShiftState;
 WheelDelta: Integer; MousePos: TPoint; var Handled: Boolean);
begin
 if WheelDelta <  then
   ScrollBox1.Perform(WM_VSCROLL,SB_LINEDOWN,)
 else
   ScrollBox1.Perform(WM_VSCROLL,SB_LINEUP,);
 if ActiveControl is TComboBox then
   if not TComboBox(ActiveControl).DroppedDown Then
     Handled:=True;
end;