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我使用 VCL 中的多态性来实现形状（矩形、平行四边形和六边形）的旋转，使用从初始形状到下一个形状的过渡，以及形状本身。面临以下问题：级联出现以下错误：

它没有显示这发生在哪一行。但是，如果以某种方式快速从第一种形式移动到第二种形式并开始移动图形，则不会出现错误，这可能是什么原因？

我附上了表格的代码（除了最初的代码，那里没有什么有趣的）：

unit Unit3;

interface

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

type
  TForm3 = class(TForm)
    Image: TImage;
    Button1: TButton;
    Timer1: TTimer;
    procedure Button1Click(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
    procedure FormActivate(Sender: TObject);
  private

  public

  end;

var
  Form3: TForm3;

implementation
{$R *.dfm}

uses unit4;

var
  t: single=0.0;
  H: THexagon;
  S: TSquare;
  P: TParall;
  Moving:Boolean=true;

procedure TForm3.Button1Click(Sender: TObject);
begin
  close;
end;




procedure TForm3.FormActivate(Sender: TObject);
begin
  H:=THexagon.Create(250,250,50,Image);
  S:=TSquare.Create(475,250,50,Image);
  P:=Tparall.Create(700,175,900,275, 150,Image);
  Timer1.Enabled:=true;
end;

procedure TForm3.Timer1Timer(Sender: TObject);
begin
  H.Move(t);
  S.Move(-0.2*t);
  P.Move(0.5*t);
  t:=t+0.5;
end;


initialization

finalization
   H.Free;
   S.Free;
   P.Free;

end.

以及具有多态性的形式：

Unit unit4;
Interface
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, ComCtrls, ExtCtrls;
Type
  TFigure=Class

    private
      x, y, halflen, dx, dy: integer;
      Image: TImage;
      procedure Draw; virtual; abstract;
      procedure Rel(t:real); virtual;

    public
      constructor Create(ax,ay,ah:integer;aImage:TImage);
      procedure Move(t:single);

    end;

    THexagon=Class(TFigure)
      private
        r: integer;
        procedure Draw; override;
      public
        constructor Create(ax, ay, ar: integer; aimage: timage);
    end;

    TSquare=Class(TFigure)
      private procedure Draw; override;
    end;

    TParall=Class(TFigure)
      private
        h:integer;
        x1, y1: integer;
        procedure Draw;override;
      public
        constructor Create(ax,ay, ax1, ay1, ah: integer; aImage:TImage );
    end;

Implementation

  Constructor TFigure.Create;
    Begin
       inherited Create;
       x := ax;
       y := ay;
       halflen := ah;
       Image := aImage;
    End;

  Procedure TFigure.Rel;
    Begin
       dx := 0;
       dy:=round(25*sin(t));
    End;

  Procedure TFigure.Move;
    Begin
       Image.Canvas.Pen.Color:=clWhite;
       Draw;
       Image.Canvas.Pen.Color:=clBlack;
       Rel(t);
       Draw;
    End;

    constructor THexagon.Create;
    begin
      inherited Create(ax,ay,ar,aImage);
      r := ar;
    end;

    procedure THexagon.Draw;
    var
      p:array[1..7] of TPoint;
      i:integer;
      a:real;
    begin
      a:=0;
      for i:=1 to 7 do begin
        p[i].X:=x+round(r*cos(a));
        p[i].Y:=y+dy-round(r*sin(a));
        a:=a+pi/3;
      end;
      p[7]:=p[1];
      with Image.Canvas do begin
          brush.Style:=bsClear;
          Polygon(p);
      end;
    end;

  Procedure TSquare.Draw;
    Begin
      image.Canvas.rectangle(180,100+dy,230,150+dy);
    End;

  Constructor TParall.Create;
    Begin
      inherited Create(ax, ay, ah, aImage);
      h := ah;
      x1:= ax1;
      y1:= ay1;
    End;

  Procedure TParall.Draw;
    Begin
      with image.Canvas do begin
        moveto(x, y + dy);
        lineto(x+h,y + dy);
        lineto(x1, y1 + dy);
        lineto(x1 - h, y1 + dy);
        lineto(x, y + dy);
      end;
    End;
end.