Project Structure

• Animals1.dpr
• AnimF.pas
• Anim.pas
• AnimF.dfm

program Animals1;

uses
  Forms,
  AnimF in 'AnimF.pas' {FormAnimals},
  Anim in 'Anim.pas';

{$R *.RES}

begin
  Application.Initialize;
  Application.CreateForm(TFormAnimals, FormAnimals);
  Application.Run;
end.

unit AnimF;

interface

uses
  SysUtils, Windows, Messages, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls, Anim;

type
  TFormAnimals = class(TForm)
    LabelKind: TLabel;
    BtnKind: TButton;
    RadioAnimal: TRadioButton;
    RadioDog: TRadioButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure BtnKindClick(Sender: TObject);
    procedure RadioAnimalClick(Sender: TObject);
    procedure RadioDogClick(Sender: TObject);
  private
    MyAnimal: TAnimal;
  end;

var
  FormAnimals: TFormAnimals;

implementation

{$R *.DFM}

procedure TFormAnimals.FormCreate(Sender: TObject);
begin
  MyAnimal := TAnimal.Create;
end;

procedure TFormAnimals.FormDestroy(Sender: TObject);
begin
  MyAnimal.Free;
end;

procedure TFormAnimals.BtnKindClick(Sender: TObject);
begin
  LabelKind.Caption := MyAnimal.GetKind;
end;

procedure TFormAnimals.RadioAnimalClick(Sender: TObject);
begin
  MyAnimal.Free;
  MyAnimal := TAnimal.Create;
end;

procedure TFormAnimals.RadioDogClick(Sender: TObject);
begin
  MyAnimal.Free;
  MyAnimal := TDog.Create;
end;

end.

unit Anim;

interface

type
  TAnimal = class
  public
    constructor Create;
    function GetKind: string;
  private
    Kind: string;
  end;

  TDog = class (TAnimal)
  public
    constructor Create;
  end;

implementation

constructor TAnimal.Create;
begin
  Kind := 'An animal';
end;

function TAnimal.GetKind: string;
begin
  GetKind := Kind;
end;

constructor TDog.Create;
begin
  Kind := 'A dog';
end;

end.

object FormAnimals: TFormAnimals
  Left = 213
  Top = 114
  Width = 287
  Height = 196
  ActiveControl = BtnKind
  Caption = 'Animals'
  Color = clBtnFace
  Font.Charset = ANSI_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = True
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  PixelsPerInch = 96
  TextHeight = 13
  object LabelKind: TLabel
    Left = 39
    Top = 120
    Width = 201
    Height = 25
    Alignment = taCenter
    AutoSize = False
    Caption = 'Kind'
    Font.Charset = ANSI_CHARSET
    Font.Color = clBlack
    Font.Height = -16
    Font.Name = 'Arial'
    Font.Style = [fsBold]
    ParentFont = False
  end
  object BtnKind: TButton
    Left = 160
    Top = 40
    Width = 81
    Height = 25
    Caption = '&Kind'
    TabOrder = 0
    OnClick = BtnKindClick
  end
  object RadioAnimal: TRadioButton
    Left = 24
    Top = 24
    Width = 105
    Height = 33
    Caption = '&Animal'
    Checked = True
    TabOrder = 1
    TabStop = True
    OnClick = RadioAnimalClick
  end
  object RadioDog: TRadioButton
    Left = 24
    Top = 56
    Width = 113
    Height = 41
    Caption = '&Dog'
    TabOrder = 2
    OnClick = RadioDogClick
  end
end