类类型的使用

unit Unit8;

interface

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

type
  TForm8 = class(TForm)
    mmo1: TMemo;
    btn1: TButton;
    procedure btn1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
  //类类型的使用
  TA = class
  protected
    Fa: integer;
  public
    constructor Create; virtual; //要是不加virtual的话,可以看看区别
    property a: Integer read Fa default 1;
  end;

  TAClass = class of TA;

  TB = class(TA)
  public
    constructor Create; override;
  end;

  TC = class(TA)
  public
    constructor Create; override;
  end;
var
  Form8: TForm8;
const
  TBCarray: array[0..1] of TAClass = (TB, TC);
implementation

{$R *.dfm}

procedure TForm8.btn1Click(Sender: TObject);
var
  i: integer;
  tmpObject: TA;
begin
  for i := 0 to 1 do
  begin
    tmpObject:= TBCarray[i].Create;
    mmo1.Lines.Add('tmpObject.ClassName: ' + tmpObject.ClassName);
    mmo1.Lines.Add('tmpObject.a: '+IntToStr(tmpObject.a));
  end;
end;

{ TA }

constructor TA.Create;
begin
  Form8.mmo1.Lines.Add('TA.Create');
  Fa:= 1;
end;

{ TB }

constructor TB.Create;
begin
  inherited Create;
  Form8.mmo1.Lines.Add('TB.Create');
  Fa:= 2;
end;

{ TC }

constructor TC.Create;
begin
  Form8.mmo1.Lines.Add('Tc.Create');
  Fa:= 3;
end;

end.