TControlStyle.csParentBackground的作用（附Delphi里的所有例子，待续）

Only applicable when Themes are enabled in applications on Windows XP. Causes the parent to draw its background into the control‘s background. This is useful for controls that need to show their parent‘s theme elements, such as aTPanel or TFrame that appears on a TPageControl. TWinControl introduces a protected ParentBackground property that includes/excludes the csParentBackground control style.

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在Controls.pas单元里的使用：

procedure TWinControl.WMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
  with ThemeServices do
  if ThemesEnabled and Assigned(Parent) and (csParentBackground in FControlStyle) then
    begin
      { Get the parent to draw its background into the control‘s background. }
      DrawParentBackground(Handle, Message.DC, nil, False);
    end
    else
    begin
      { Only erase background if we‘re not doublebuffering or painting to memory. }
      if not FDoubleBuffered or
         (TMessage(Message).wParam = TMessage(Message).lParam) then
        FillRect(Message.DC, ClientRect, FBrush.Handle);
    end;

  Message.Result := 1;
end;

procedure TWinControl.CMInvalidate(var Message: TMessage);
var
  I: Integer;
begin
  if HandleAllocated then
  begin
    if Parent <> nil then Parent.Perform(CM_INVALIDATE, 1, 0);
    if Message.WParam = 0 then
    begin
      InvalidateRect(FHandle, nil, not (csOpaque in ControlStyle));
      { Invalidate child windows which use the parentbackground when themed }
      if ThemeServices.ThemesEnabled then
        for I := 0 to ControlCount - 1 do
          if csParentBackground in Controls[I].ControlStyle then
            Controls[I].Invalidate;
    end;
  end;
end;

function TWinControl.GetParentBackground: Boolean;
begin
  Result := csParentBackground in ControlStyle;
end;

procedure TWinControl.SetParentBackground(Value: Boolean);
begin
  if ParentBackground <> Value then
  begin
    if Value then
      ControlStyle := ControlStyle + [csParentBackground]
    else
      ControlStyle := ControlStyle - [csParentBackground];
    Invalidate;
  end;
end;

问题是，D7里的ThemeServices.ThemesEnabled始终都是False，即使使用了Windows皮肤也是如此，莫非需要做什么额外的设置？