Access Violation in delphi...

Hi .I have the follow class:

TElectricBlock = class(TCustomDiagramBlock)

  private

    FTextAlign: TBlockTextAlign;

    {$IFDEF GDIPLUS}

    FPath: TGPGraphicsPath;

    {$ENDIF}

    procedure SetTextAlign(const Value: TBlockTextAlign);

    procedure CreateLinkPoints;

  protected

    {$IFDEF GDIPLUS}

    property DrawPath: TGPGraphicsPath read FPath;

    {$ENDIF}

  public

    constructor Create(AOwner: TComponent); override;

    destructor Destroy; override;

    {$IFDEF GDIPLUS}

    procedure GetBlockPath(APath: TGPGraphicsPath); override;

    {$ENDIF}

  published

    property TextAlign: TBlockTextAlign read FTextAlign write SetTextAlign;

    property Angle;

    property Brush;

    property SelBrush;

    property Color;

    property SelColor;

    property Pen;

    property Strings;

    property Alignment;

    property VertAlign;

    property ClipText;

    property WordWrap;

    property TextCells;

    property Restrictions;

    property Font;

    property DiagramFont;

    property MinWidth;

    property MinHeight;

    property Shadow;

    property ShowHint;

    property Hint;

    property ParentShowHint;

    property Gradient;

    property Bitmap;

    property BitmapMode;

    property BitmapTransparent;

    property MetaFile;

    property Picture;

    property PictureMode;

    property Transparent;

    property Cursor;

    property StringData;

    property Visible;

    property Layer;

    property Transparency;

  end;

 

 

constructor TElectricBlock.Create(AOwner: TComponent);

begin

  inherited;

  {$IFDEF GDIPLUS}

  FPath := TGPGraphicsPath.Create;

  {$ENDIF}

  Shape := bsNoShape;

  {OriginalRect has the easiest rect to draw, but width and height have

   the best default size of the block}

  Drawer.OriginalRect := Rect(0, 0, 80, 40);

  {$IFDEF GDIPLUS}

  GPDrawer.SourceRect := RectX(0, 0, 80, 40);

  {$ENDIF}

  {Call TextAlign (not FTextAlign) to update textcell. Call after changing OriginalRect}

  TextAlign := taRightBottom;

  UpdateBlockHandles; {Call UpdateBlockHandles after changing OriginalRect}

  CreateLinkPoints;

  MinWidth := 20;

  MinHeight := 20;

  Width := 60;

  Height := 20;

  RotateFont := False;

  ClipText := False;

end;

 

procedure TElectricBlock.CreateLinkPoints;

begin

  {Create points at left and right of block, vertically centered. Points are

   relative to Drawer.OriginalRect

   Also defined the orientation of lines linked to the point}

  with Drawer.OriginalRect do

  begin

    LinkPoints.Add(Left, (Bottom - Top) div 2, aoLeft);

    LinkPoints.Add(Right, (Bottom - Top) div 2, aoRight)

  end;

end;

 

destructor TElectricBlock.Destroy;

begin

  {$IFDEF GDIPLUS}

  FPath.Free;

  {$ENDIF}

  inherited;

end;

 

{$IFDEF GDIPLUS}

procedure TElectricBlock.GetBlockPath(APath: TGPGraphicsPath);

begin

  {Set the block path as a rectangle because we need to set that area as

   the selectable area. We will paint the control in the DrawBlock method}

  APath.AddRectangle(RectGP(GPDrawer.SourceRect));

end;

{$ENDIF}

 

procedure TElectricBlock.SetTextAlign(const Value: TBlockTextAlign);

begin

  if FTextAlign <> Value then

  begin

    FTextAlign := Value;

    With Drawer.OriginalRect do

      Case FTextAlign of

        taLeftTop:

          DefaultTextCell.SetBounds(0, -(Bottom - Top), Right - Left, Bottom - Top);

        taRightBottom:

          DefaultTextCell.SetBounds(0, Bottom - Top, Right - Left, Bottom - Top);

      end;

    Redraw;

  end;

end;

 

In another unit i have such code:


type
  IMyInterface = Interface(IInterface)
       ['{11BBD2CA-04BC-45AE-8CA2-378CCFCB221F}']
  procedure Dotest;
  end;

type
  TNPNTransistor = class(TElectricBlock,IMyInterface)
  protected
  procedure DrawBlock(Canvas: TCanvas; ARect: TRect); override;
  public
  constructor Create(AOwner: TComponent);
  procedure Dotest;
  end;


constructor TNPNTransistor.Create(AOwner: TComponent);
begin
  inherited;
  Drawer.OriginalRect := Rect(0, 0, 80, 80);
  {$IFDEF GDIPLUS}
  GPDrawer.SourceRect := RectX(0, 0, 80, 80);
  {$ENDIF}
  UpdateBlockHandles; {Call UpdateBlockHandles after changing OriginalRect}
  Width := 40;
  Height := 40;
  with Drawer.OriginalRect do
  begin
    LinkPoints.Clear;
    LinkPoints.Add(Right, Bottom , aoNone);
    LinkPoints.Add(Left, (Bottom - Top) div 2, aoNone);
    LinkPoints.Add(Right, Top , aoNone);
  end;
end;

procedure TNPNTransistor.DrawBlock(Canvas: TCanvas; ARect: TRect);
var w ,h,x : integer;
begin
  w := 20;
  h := 10;
   {$IFDEF GDIPLUS}
    With DrawPath do
    begin
      Reset;
      StartFigure;
       AddArc(0,0,w,h,45,270);
      CloseFigure;
    end;
    GPDrawer.GPCanvas.Pen.Transparency := Self.Transparency;
    GPDrawer.GPCanvas.Pen.Assign(Self.Pen);
    GPDrawer.TransformPath(DrawPath);
    GPDrawer.GPCanvas.DrawPath(DrawPath);
    {$ENDIF}
  end;


 procedure TNPNTransistor.Dotest;
begin
 with Drawer.OriginalRect do
  begin
    LinkPoints.Add(Right, Bottom , aoNone);
    LinkPoints.Add(Left, (Bottom - Top) div 8, aoNone);
    LinkPoints.Add(Right/2, Top , aoNone);
    LinkPoints.Add(Right/2, Top/3 , aoNone);
  end;
 {$IFDEF GDIPLUS}
    With Self.DrawPath do
    begin
      StartFigure;
       AddArc(0,0,10,40,45,270);
      CloseFigure;
    end;
    GPDrawer.GPCanvas.Pen.Transparency := Self.Transparency;
    GPDrawer.GPCanvas.Pen.Assign(Self.Pen);
    GPDrawer.TransformPath(DrawPath);
    GPDrawer.GPCanvas.DrawPath(DrawPath); <--------------(*)
    {$ENDIF}
  end;


In main form  I create an object of TNPNTransistor.
The DrawBlock is called automatically.
 Everything works nice and i get my shape painted in
the  diagram, a component that holds all the blocks.

procedure TTMSForm1.DrawClick(Sender: TObject);
var npn:  TNPNTransistor;
begin
npn := TNPNTransistor.Create(Owner);
npn.Diagram := floor;
end;

A doubleclik on the shape just created should excute the Dotest method:

procedure TTMSForm1.floorDControlDblClick(Sender: TObject; ADControl: TDiagramControl);
Var ImyInterf2 :   IMyInterface2 ;
    ImyInterf :   IMyInterface ;
begin
(ADControl as  TNPNTransistor).DoTest;
end;

It works for the first part of the DoTest procedure. I get an Access Violation because
of this line:

    GPDrawer.GPCanvas.DrawPath(DrawPath); <--------------(*)

I am not able to find out the reason. Any help?

Thx