مشكلة في إظهار ScrollBar مع إستعمال TStyle ؟

PHP كود :

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs,Vcl.Themes,Vcl.Styles, Vcl.StdCtrls;

  type TFormStyleHookNC= class(TMouseTrackControlStyleHook)
  protected
    procedure PaintBackground(Canvas: TCanvas); override;
    constructor Create(AControl: TWinControl); override;
  end;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
 constructor TFormStyleHookNC.Create(AControl: TWinControl);
begin
  inherited;
  OverrideEraseBkgnd := True;
end;

procedure TFormStyleHookNC.PaintBackground(Canvas: TCanvas);
var
  Details: TThemedElementDetails;
  R: TRect;
begin
  if StyleServices.Available then
  begin
    Details.Element := teWindow;
    Details.Part := 0;
    R := Rect(0, 0, Control.ClientWidth, Control.ClientHeight);
    StyleServices.DrawElement(Canvas.Handle, Details, R);

  end;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
Self.AutoScroll:=True;
end;

initialization
TStyleManager.Engine.RegisterStyleHook(TForm1, TFormStyleHookNC);

end.

PHP كود :

unit Unit1;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs,Vcl.Themes,Vcl.Styles, Vcl.StdCtrls,
  Vcl.CheckLst;

type TStyledScrollBox=class(TScrollBoxStyleHook)
private
FCanvas:TCanvas;
public
   constructor Create(AControl: TWinControl); override;
   destructor Destroy; override;
   procedure DrawBorder; override;
   procedure PaintBackground(Canvas: TCanvas); override;
   procedure Paint(Canvas: TCanvas); override;

end;
type
  TForm1 = class(TForm)
    ScrollBox1: TScrollBox;
    ListBox1: TListBox;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin

end;

{ TStyledScrollBox }

constructor TStyledScrollBox.Create(AControl: TWinControl);
begin
  inherited;
   Brush.Color := StyleServices.GetStyleColor(scWindow);
   FCanvas:=TCanvas.Create;

end;

destructor TStyledScrollBox.Destroy;
begin
 FreeAndNil(FCanvas);

  inherited;
end;

procedure TStyledScrollBox.DrawBorder;
begin
 inherited;
 FCanvas.Handle:=GetWindowDc(Handle);
 FCanvas.Brush.Color:=StyleServices.GetStyleColor(scWindow);
 FCanvas.FrameRect(Rect(0,0,Control.Width,Control.Height));
 FCanvas.FrameRect(Rect(1,1,Control.Width-1,Control.Height-1));

end;

procedure TStyledScrollBox.Paint(Canvas: TCanvas);
begin
  inherited;

end;

procedure TStyledScrollBox.PaintBackground(Canvas: TCanvas);
begin
  inherited;

end;

initialization
TStyleManager.Engine.RegisterStyleHook(TScrollBox,TStyledScrollBox);
end.