多线程基础问题

[neowang]

刚刚开始接触多线程，下面是使用Delphi 7照“Delphi 6开发人员指南”上的一个例子做的,可是编译报错：[Fatal Error] Main.pas(7): Circular unit reference to 'Main'。请问这个循环的引用怎么解决呢？
源码
unit Main;

interface

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

type
TForm1 = class(TForm)
Memo1: TMemo;
Edit1: TEdit;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
NewThread:TMyThread;
begin
NewThread:=TMyThread.Create(False);

end;

end.

unit MyThread;

interface

uses
Classes,Main;

type
TMyThread = class(TThread)
private
{ Private declarations }
Answer:Integer;
protected
procedure Execute; override;
procedure GiveAnswer;
end;

implementation

{ TMyThread }

procedure TMyThread.GiveAnswer;
begin
Form1.Edit1.Text:=IntToStr(Answer);
end;

procedure TMyThread.Execute;
var
i:Integer;
begin
{ Place thread code here }
FreeOnTerminate:=true;
for i:=i to 2000000 do
begin
if Terminated then break;
inc(Answer,Round(Abs(Sin(Sqrt(i)))));
Synchronize(GiveAnswer);
end;
end;

end.

[zjybestzjybest]

unit MyThread;

interface

uses
Classes;

type
TMyThread = class(TThread)
private
{ Private declarations }
Answer:Integer;
protected
procedure Execute; override;
procedure GiveAnswer;
end;

implementation
uses
Main;

{ TMyThread }

procedure TMyThread.GiveAnswer;
begin
Form1.Edit1.Text:=IntToStr(Answer);
end;

procedure TMyThread.Execute;
var
i:Integer;
begin
{ Place thread code here }
FreeOnTerminate:=true;
for i:=i to 2000000 do
begin
if Terminated then break;
inc(Answer,Round(Abs(Sin(Sqrt(i)))));
Synchronize(GiveAnswer);
end;
end;

end.

[lxpbuaa]

将引用放在实现（impelement）而不是接口（interface）部分就可以了。

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宠辱不惊，看庭前花开花落，去留无意；毁誉由人，望天上云卷云舒，聚散任风。
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[neowang]

呵呵，是我太粗心了。
但是能不能解释一下为什么这样就不是“循环的单元引用”了呢？

[answerfish]

turtle