Delphi-PRAXiS - Delphi Forward in Klassen funktioniert nicht

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Delphi-PRAXiS (https://www.delphipraxis.net/forum.php)

- Programmieren allgemein (https://www.delphipraxis.net/40-programmieren-allgemein/)

- - Delphi Forward in Klassen funktioniert nicht (https://www.delphipraxis.net/183178-forward-klassen-funktioniert-nicht.html)

Forward in Klassen funktioniert nicht

Hallo ich mache da wohl einen Denkfehler und komme nicht drauf

Delphi-Quellcode:

			type

  // Define the classes in this Unit at the very start for clarity

  TForm1 = Class;          // This is a forward class definition

  TFruit = Class(TObject)  // This is an actual class definition :

    // Internal class field definitions - only accessible in this unit

     private

       t        : TForm1;  // Warum ist die variable ungültig !

       isRound  : Boolean;

       length   : single;

       width    : single;

       diameter : single;

    // Fields and methods only accessible by this class and descendants

    procedure SetForm(const Value : TForm1);

     protected

    // Externally accessible fields and methods

     public

      // 2 constructors - one for round fruit, the other long fruit

       constructor Create(diameter : single);               overload;

       constructor Create(length : single; width : single); overload;

    // Externally accessible and inspectable fields and methods

     published

      // Note that properties must use different names to local defs

       property round : Boolean

         read   isRound;

       property len   : single

         read   length;

       property wide  : single

         read   width;

       property diam  : single

         read   diameter;

  end;                    // End of the TFruit class definition

  // The actual TForm1 class is now defined

   TForm1 = Class(TForm)

    Button1: TButton;

    Button2: TButton;

     procedure FormCreate(Sender: TObject);

     procedure ShowFruit(fruit : TFruit);

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

   private

    // No local data

    f : TFruit;

   public

    // Uses just the TForm ancestor class public definitions

   end;

 var

   Form1: TForm1;

 implementation

 {$R *.dfm}

// Create a round fruit object

 constructor TFruit.Create(diameter: single);

 begin

  // Indicate that we have a round fruit, and set its size

   isRound       := true;

   self.diameter := diameter;

 end;

// Create a long fruit object

 constructor TFruit.Create(length, width: single);

 begin

  // Indicate that we have a long fruit, and set its size

   isRound     := false;

   self.length := length;

   self.width  := width;

 end;

 procedure TFruit.SetForm(const Value : TForm1);

 var

 f1 : TForm1;

 begin

   t := nil;  // Nicht mal das geht

   f1 := Value; // Das würde gehen

   t := Value; // und das ist der Grund für den Eintrag

 end;

// Form object - action taken when the form is created

 procedure TForm1.Button1Click(Sender: TObject);

begin

FormCreate(Sender);

end;

procedure TForm1.Button2Click(Sender: TObject);

 var

 Fruit : TFruit;

begin

 Fruit := TFruit.Create(23);

  ShowFruit(Fruit);

end;

procedure TForm1.FormCreate(Sender: TObject);

 var

   apple, banana : TFruit;

 begin

 f.SetForm(self);

  // Let us create our fruit objects

   apple  := TFruit.Create(3.5);

   banana := TFruit.Create(7.0, 1.75);

  // Show details about our fruits

   ShowFruit(apple);

   ShowFruit(banana);

 end;

// Show what the characteristics of our fruit are

 procedure TForm1.ShowFruit(fruit: TFruit);

 begin

   if fruit.round

   then ShowMessage('We have a round fruit, with diam = '+

                    FloatToStr(fruit.diam))

   else

   begin

     ShowMessage('We have a long fruit');

     ShowMessage('    it has length = '+FloatToStr(fruit.len));

     ShowMessage('    it has width  = '+FloatToStr(fruit.wide));

   end;

 end;

 end.

http://www.delphibasics.co.uk/RTL.asp?Name=Class
Ich habe das Beispiel ein wenig abgeändert
Meine Frage wie kann ich dem Object TFruit
mitteilen das TForm1 Object mitteilen.