Program Errors when trying to change forms

Question

I firstly created a form that will show settings. Then i created a login box that will load a password from an ini file. I originally thought that it was an error with loading the ini file. Though I have isolated it to when I load the settings form. Here is the code for all of them.

The code for the settings screen:

    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.

The code for the login form:

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.

This is the project:

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.

Where do you create Form1? (BTW, you can assign the same event handler to multiple components.) — Sertac Akyuz, Aug 01 '12 at 00:44
when i click the login button it throws errors, something about CPU errors or something and the program crashes. It is then stuck in degug mode and i'm forced to reset the program. — Matt Biggs, Aug 01 '12 at 00:56
Access violation at address 0043Af32 in module 'Project1.exe'. Read of address 0000002C0 — Matt Biggs, Aug 01 '12 at 01:02
@Matt - That's because you've commented out the statement in the project file that creates 'Form1' (see the first comment to your question), and you're not instantiating 'Form1' elsewhere either. — Sertac Akyuz, Aug 01 '12 at 01:08
Right, well when I do that and I start the program it opens botht he forms though I have the Settings form visable = false in the object inspector. :/ — Matt Biggs, Aug 01 '12 at 01:12
Perhaps you should open a new question that specifically asks how to do what it is you're trying to do, and someone here can help you solve it. Finish dealing with this question, and then start a new one that describes the problem you're trying to solve, and we'll help you figure out how to accomplish it. — Ken White, Aug 01 '12 at 02:49
" Then i created a login box that will load a password from an ini file. " ...sounds like not secure way to store password. — Hendra, Aug 01 '12 at 08:26
You should 1) 1st create Form2 and after that create Form1 *and* 2) move all the code from Form2.OnCreate into Form2.OnShow. You are misusing OnCreate event here — Arioch 'The, Aug 02 '12 at 08:51

Ken White · Answer 1 · 2012-08-01T01:28:34.380

You've commented out the line of code in the .dpr file that createsForm1`:

  //Application.CreateForm(TForm1, Form1);

But you're accessing that uncreated form in Unit1:

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

Uncomment the line in the project file so it gets created. Note that the first form that's created with Application.CreateForm becomes your application's main form, and when that form is closed your application terminates.

You also have another major flaw in your code. You should never reference the form itself by name from within one of it's own methods, like you do here from within TForm2.LoginButtonClick:

    Form2.Hide;

This means that if you ever rename the form, it won't compile, and if you create more than one TForm2, your code will either access the wrong one or will cause access violations for accessing a non-created form (like the problem you're having now). You should either just use the form's method directly, like Hide;' from the method, or useSelf.Hide;` to refer to the instance currently running the method.

(For future reference: When you have a problem, it helps if you explain what that problem is when you ask for help solving it. "Program errors" with no other information about the error is meaningless by itself. When you type "error", the very next thing you should add is the exact error you're having, including the exact error message including any address information. We can't see your screen from where we sit, so we only have the info you provide us to go by in helping you.)

Program Errors when trying to change forms

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