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;interfaceusesWindows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, StdCtrls;typeTForm1 = 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 TBassTBass = classprocedure msg1;end;TChild = class(TBass)procedure msg2;end;varForm1: TForm1;implementation{$R *.dfm}{ TBass }
procedure TBass.msg1;
beginShowMessage('is Bass');
end;{ TChild }
procedure TChild.msg2;
beginShowMessage('is Child');
end;//测试1: 父类只有一个方法 msg1
procedure TForm1.Button1Click(Sender: TObject);
varb: TBass;
beginb := 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);
varc: TChild;
beginc := TChild.Create;c.msg1; {is Bass}c.msg2; {is Child}c.Free;
end;end.