delphi 如何让一个窗口重新打开

主窗体unit

主窗体对象,

通过主窗体打开一个子窗体.

子窗体在implement里循环引用了主窗体unit,
子窗体做完事情后关闭, 想调用主窗体的close方法,让他关闭,可是没反应,主窗体关不掉,怎么办呀?
但调用他的其他方法就可以了,为什么呀?

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什么代码？

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unit OrderNewBookUnit;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, TntStdCtrls, Grids,
  TntGrids, YxAdvSGrid,UpdateOrderUnit;
type
  TOrderNewBookForm = class(TForm)
///////////////////////
procedure TOrderNewBookForm.updateTntButtonClick(Sender: TObject);
var
  updateOrderForm:TupdateOrderForm;
begin
    updateOrderForm:=TupdateOrderForm.Create(self);
    updateOrderForm.YxAdvSGrid1:=YxAdvSGrid1;
    updateOrderForm.FormStyle := fsMDIChild;
    updateOrderForm.Show;
end;


///子窗体的代码:
unit UpdateOrderUnit;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, TntStdCtrls, ExtCtrls, TntExtCtrls,
  YxAdvSGrid,unitDataType,UnitPublic,UnitConst
type
  TupdateOrderForm = class(TForm)
var
  updateOrderForm: TupdateOrderForm;
  issuingData