尝试更改表单时出现程序错误

Question

我首先创建了一个显示设置的表单。然后我创建了一个登录框，它将从 ini 文件加载密码。我最初认为这是加载 ini 文件时的错误。虽然我已经隔离了它，当我加载设置表单时。这是所有这些代码。

设置屏幕的代码：

    unit Unit1;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, inifiles;
type
  TForm1 = class(TForm)
    SaveButton: TButton;
    AEditA: TEdit;
    AEditB: TEdit;
    SEditB: TEdit;
    PEditB: TEdit;
    PLabelA: TLabel;
    SLabelA: TLabel;
    ALabelA: TLabel;
    PEditA: TEdit;
    SEditA: TEdit;
    ExitButton: TButton;
    Settings: TLabel;
    ALabelB: TLabel;
    SLabelB: TLabel;
    PLabelB: TLabel;
    AReserveLabel: TLabel;
    BReserveLabel: TLabel;
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    Label5: TLabel;
    Label6: TLabel;
    Label8: TLabel;
    Label7: TLabel;
    procedure SaveButtonClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure ExitButtonClick(Sender: TObject);
    procedure AEditAKeyPress(Sender: TObject; var Key: Char);
    procedure AEditBKeyPress(Sender: TObject; var Key: Char);
    procedure SEditAKeyPress(Sender: TObject; var Key: Char);
    procedure SEditBKeyPress(Sender: TObject; var Key: Char);
    procedure PEditAKeyPress(Sender: TObject; var Key: Char);
    procedure PEditBKeyPress(Sender: TObject; var Key: Char);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
  IniFile : TIniFile;
  appINI : TIniFile;
  APriceA : String;
  SPriceA : String;
  PPriceA : String;
  APriceB : String;
  SPriceB : String;
  PPriceB : String;
implementation

{$R *.DFM}
procedure TForm1.SaveButtonClick(Sender: TObject);
//Save Button
 begin
  appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini'));
  APriceA := (AEditA.Text);
  SPriceA := (SEditA.Text);
  PPriceA := (PEditA.Text);
  APriceB := (AEditB.Text);
  SPriceB := (SEditB.Text);
  PPriceB := (PEditB.Text);
  appINI.WriteString('PricesA','Adult',APriceA);
  appINI.WriteString('PricesA','Student',SPriceA);
  appINI.WriteString('PricesA','Pensioner',PPriceA);
  appINI.WriteString('PricesB','Adult',APriceB);
  appINI.WriteString('PricesB','Student',SPriceB);
  appINI.WriteString('PricesB','Pensioner',PPriceB);
  appINI.Free;
  ShowMessage('Settings Saved Successfully!');
 end;
procedure TForm1.FormCreate(Sender: TObject);
//Displays values as the form is created
begin
{ appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini'));
APriceA := appINI.ReadString('PricesA','Adult','');
SPriceA := appINI.ReadString('PricesA','Student','');
PPriceA := appINI.ReadString('PricesA','Pensioner','');
APriceB := appINI.ReadString('PricesB','Adult','');
SPriceB := appINI.ReadString('PricesB','Student','');
PPriceB := appINI.ReadString('PricesB','Pensioner','');
appINI.Free;
AEditA.Text := (APriceA);
SEditA.Text := (SPriceA);
PEditA.Text := (PPriceA);
AEditB.Text := (APriceB);
SEditB.Text := (SPriceB);
PEditB.Text := (PPriceB);}
end;
procedure TForm1.ExitButtonClick(Sender: TObject);
//Exit Button
begin
Close;
end;
procedure TForm1.AEditAKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
procedure TForm1.AEditBKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
procedure TForm1.SEditAKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
procedure TForm1.SEditBKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
procedure TForm1.PEditAKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
procedure TForm1.PEditBKeyPress(Sender: TObject; var Key: Char);
var s:string;
begin
  s := ('1234567890.'#8); //Add chars you want to allow
  if pos(key,s) =0 then begin
    Key:=#0;
    showmessage('Only Numbers are allowed. Include cents!');
  end;
end;
//End of Settings
end.

登录表单的代码：

unit Unit2;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, Mask, inifiles, Unit1;
type
  TForm2 = class(TForm)
    PassEdit: TMaskEdit;
    LoginButton: TButton;
    PassLabel: TLabel;
    InvisiButton: TButton;
    procedure PassEditClick(Sender: TObject);
    procedure LoginButtonClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form2: TForm2;
  IniFile : TIniFile;
  appINI : TIniFile;
  Password : string;
implementation

{$R *.DFM}
procedure TForm2.PassEditClick(Sender: TObject);
begin
PassEdit.Text := '';
end;
procedure TForm2.LoginButtonClick(Sender: TObject);
begin
//if Password = PassEdit.Text then begin
Form2.Hide;
showmessage('test');
Form1.Show;
end;
//end;
procedure TForm2.FormCreate(Sender: TObject);
begin
appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini'));
Password := appINI.ReadString('Login','Password','');
ShowMessage(Password);
appINI.Free;
end;
end.

这是项目：

program Project1;
uses
  Forms,
  Unit1 in 'Unit1.pas' {Form1},
  Unit2 in 'Unit2.pas' {Form2};

{$R *.RES}
begin
  Application.Initialize;
  //Application.CreateForm(TForm1, Form1);
  Application.CreateForm(TForm2, Form2);
  Application.Run;
end.

Answer 1

您已经注释掉了 Form1 .dpr file that creates中的代码行：

  //Application.CreateForm(TForm1, Form1);

但是您正在Unit1访问该未创建的形式：

procedure TForm2.LoginButtonClick(Sender: TObject);
begin
//if Password = PassEdit.Text then begin
Form2.Hide;
showmessage('test');
Form1.Show;        // <-- Accessing uncreated form here
end;

取消注释项目文件中的行，以便创建该行。请注意，使用 Application.CreateForm 创建的第一个窗体将成为应用程序的主窗体，当该窗体关闭时，应用程序将终止。

您的代码中还有另一个主要缺陷。您永远不应该从它自己的方法之一中按名称引用表单本身，就像您在 TForm2.LoginButtonClick 中所做的那样：

    Form2.Hide;

这意味着，如果您重命名表单，它将无法编译，并且如果您创建多个TForm2，您的代码将访问错误的代码，或者会导致访问未创建表单的访问冲突(就像您现在遇到的问题(。您应该直接使用表单的方法，例如Hide;' from the method, or use Self.Hide;"来引用当前运行该方法的实例。

(供将来参考：当您遇到问题时，当您寻求帮助解决问题时，如果您解释该问题是什么，这会有所帮助。没有关于错误的其他信息的"程序错误"本身毫无意义。当您键入"error"时，您应该添加的下一件事是您遇到的确切错误，包括包含任何地址信息的确切错误消息。我们无法从我们所在的位置看到您的屏幕，因此我们只有您提供给我们的信息来帮助您。