访问用PageControl封装的窗体变量报内存错误，请教高人

[richardi]

我用PageControl封装窗体，当窗体创建后，再读取已创建的窗体变量时报内存错误，下面是所有代码：

program ShowFormDemo;

uses
Forms,
Unit1 in 'Unit1.pas' {Form1},
Unit2 in 'Unit2.pas' {Form2}

{$R *.res}

begin
Application.Initialize;
Application.CreateForm(TForm1, Form1); //注意，这里只创建Form1,其它窗体动态创建，如果都先创建就不报错
Application.Run;
end.


//下面是主窗体
unit Unit1;

interface

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

type
TForm1 = class(TForm)
Button1: TButton;
PageControl1: TPageControl;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
procedure ShowForm(AClass:TComponentClass;AForm:TForm);
{ Public declarations }
end;

var
Form1: TForm1;

implementation
uses Unit2,Unit3;
{$R *.dfm}
procedure TForm1.ShowForm(AClass:TComponentClass;AForm:TForm);//封装窗体的函数
var Tabsht: TTabSheet;
begin
Tabsht := TTabSheet.Create(Application);
Tabsht.PageControl:=PageControl1;
application.CreateForm(AClass,AForm);
AForm.Parent:=Tabsht;
Tabsht.Tag:=Integer(AForm);
AForm.BorderStyle:=bsNone;
AForm.Align:=alClient;
AForm.show;
Tabsht.Caption:=AForm.Caption;
PageControl1.ActivePage := Tabsht;
Tabsht.Show;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowForm(TForm2,Form2);
Form2.FVal:=100;//这里报错
end;
end.

//下面是Form2窗体
unit Unit2;

interface

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

type
TForm2 = class(TForm)
private
{ Private declarations }
public
FVal:Integer;//只定义一个变量
{ Public declarations }
end;

var
Form2: TForm2;

implementation

{$R *.dfm}

end.

如果2个窗体在工程文件中都先创建好了，就不会报错，我怀疑在ShowForm(TForm2,Form2)后，Form2是局部变量，导致访问出错，可是我创建时用的application.CreateForm(AClass,AForm);它的owner应该是Application这个全局对象啊，怎么回出错呢，请高人指点，谢谢。

[广州佬]

请按下面代码修改：

......
  public
    { Public declarations }
    procedure ShowForm(AClass:TComponentClass;var AForm:TForm);
  end;

var
  Form1: TForm1;

implementation
uses Unit2,Unit3;


{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var Fm2:TForm;
begin
  ShowForm(TForm2,Fm2);
  TForm2(Fm2).FVal:=100;
end;

procedure TForm1.ShowForm(AClass: TComponentClass;var AForm: TForm);
var Tabsht: TTabSheet;
begin
......
end;

......

[广州佬]

或者，你原来的其他代码不变，仅将点击按钮事件代码按下面修改，就明白原因了：

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowForm(TForm2,Form2);
  if Form2<>nil then
    Form2.FVal:=100//这里报错
  else
    showmessage('Form2的实例不存在。');
end;

[广州佬]

又或者这样改（但很明显，不符合你的用途）：

......

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, StdCtrls, Unit2, Unit3;

......

  public
    { Public declarations }
    procedure ShowForm(AClass:TComponentClass; var AForm:TForm2);
  end;

var
  Form1: TForm1;

implementation
//uses Unit2,Unit3;

{$R *.dfm}

......

procedure TForm1.ShowForm(AClass: TComponentClass; var AForm: TForm2);
var Tabsht: TTabSheet;
begin
......
end;

......

[jAmEs_]

[Quote=引用 1 楼 的回复:]

请按下面代码修改：
Delphi(Pascal) code

......
public
{ Public declarations }
procedure ShowForm(AClass:TComponentClass;var AForm:TForm);
end;

var
Form1: TForm1;

implementation
uses Unit2,Un……
[/Quote]这个对lz意义大些

[kaikai_kk]

ShowForm用var

procedure ShowForm(AClass:TComponentClass;var AForm:TForm);