理解 Delphi 的类(五) - 认识类的继承

先新建一个 VCL Forms Application 工程, 代码中就已经出现了两个 类:
一个是 TForm 类; 一个是 TForm1 类; TForm1 继承于 TForm.
TForm 是 TForm1 的父类; TForm1 是 TForm 的子类.

---

unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    Button2: TButton;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

  end;



  //下面自定义了两个类, TChild 继承于 TBass

  TBass = class

    procedure msg1;

  end;



  TChild = class(TBass)

    procedure msg2;

  end;





var

  Form1: TForm1;



implementation



{$R *.dfm}



{ TBass }

procedure TBass.msg1;

begin

  ShowMessage('is Bass');

end;



{ TChild }

procedure TChild.msg2;

begin

  ShowMessage('is Child');

end;







//测试1: 父类只有一个方法 msg1

procedure TForm1.Button1Click(Sender: TObject);

var

  b: TBass;

begin

  b := TBass.Create;

  b.msg1; {is Bass}

  b.Free;

end;



//测试2: 子类有两个方法, 自己一个 msg2, 还继承了一个 msg1

procedure TForm1.Button2Click(Sender: TObject);

var

  c: TChild;

begin

  c := TChild.Create;

  c.msg1; {is Bass}

  c.msg2; {is Child}

  c.Free;

end;



end.