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.