如何在RichEdit上捕获OnScroll事件？

procedure TCustomRich.WMVScroll(var Msg : TWMVScroll);
begin
  inherited;
  if (Msg.ScrollCode in [SB_THUMBTRACK, SB_THUMBPOSITION]) then
    FScrollY := Msg.Pos;
  if Assigned(OnScroll) then
    OnScroll(Self, FScrollX, FScrollY);
end;

procedure TCustomRich.WMHScroll(var Msg : TWMVScroll);
begin
  inherited;
  if (Msg.ScrollCode in [SB_THUMBTRACK, SB_THUMBPOSITION]) then
    FScrollX := Msg.Pos;
  if Assigned(OnScroll) then
    OnScroll(Self, FScrollX, FScrollY);
end;