unit Unit1;

interface

uses
Windows, Messages, SysUtils,
Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, Unit2,
ExtCtrls;
type
TForm1 = class(TForm)
Button1:
TButton;
Button2: TButton;
Panel1: TPanel;
Label1:
TLabel;
procedure Button1Click(Sender: TObject);
procedure
Button2Click(Sender: TObject);
private
{ Private declarations
}
public
{ Public declarations }
end;
var

Form1: TForm1;
implementation
{$R *.dfm}
procedure
TForm1.Button1Click(Sender: TObject);
var s:Tmemorystream;

rr:Twriter;
ff:TFrame2;
begin
ff:=TFrame2.Create
(self);
ff.Parent :=Panel1;
s:=Tmemorystream.Create ;

s.WriteComponent(ff);
s.SaveToFile('a');
s.Free;
end;

procedure TForm1.Button2Click(Sender: TObject);
var

s:Tmemorystream;
ff:TFrame2;
begin

classes.RegisterClass(TFrame2);
classes.RegisterClass(Tlabel);

classes.RegisterClass(TButton);
s:=Tmemorystream.Create ;

s.LoadFromFile('a');
ff := TFrame2(TFrame.Create(Self));

ff.Parent :=self;
s.ReadComponent(ff) ;
s.Free;

end;

为什么要RegisterClass(TFrame2)?我在interface引用了Unit2呀，上述代码执行后，报错，提示'Class
TLabel not found',这是为何？也要RegisterClass(TLabel)吗？为什么呢？为什么也还要RegisterClass(TButton)呢？在TForm的Publisher部分有TLabel呀

定义时TButton和TLabel的类信息是否就注册到运行时信息库中了?
如果是，那为何在后面还要用RegisterClass(TButton)和RegisterClass(TLabel)呢？

不明白，还请各位大大指点，谢谢！