Close current form when opening other form

[Lainkes 0]

Hello,

 

I have a form with a button. When the button is clicked, a new form opens to input data.

So when this button is clicked, I need to close the current form with the button. 

This is my code :

Quote

 // OPEN INPUT SCREEN FOR BOR DOSSIER
                  try
                    inputCheckForm := Tfrm_InputCheck.Create(Self);
                    try
                      inputCheckForm.ShowModal;
                    finally
                      inputCheckForm.Free;
                      Close; // CLOSE THE CURRENT INPUT FORM
                    end;
                  except
                    on E: Exception do
                      DoShowException(E);
                  end;

 

I have put the Close command in the Finally section. But that's not working.

I thought that was the right place, so that even in case of an error the screen is closed.

Maybe I'm thinkin wrong.

Thanks for your feedback.

 

Alain

[Lajos Juhász 291]

The correct code would be:

 

// OPEN INPUT SCREEN FOR BOR DOSSIER
                  try
                    inputCheckForm := Tfrm_InputCheck.Create(Self);
                    try
                      inputCheckForm.ShowModal;
                    finally
                      inputCheckForm.Free;
                      Release; // CLOSE THE CURRENT INPUT FORM
                    end;
                  except
                    on E: Exception do
                      DoShowException(E);
                  end;
 

https://docwiki.embarcadero.com/Libraries/Athens/en/Vcl.Forms.TCustomForm.Release

[Uwe Raabe 2051]

The question is: Do you want the current form to close before you have entered the data in the new one or after that?

[Lainkes 0]

Thanks. This works as the called form is closed.

So this works fine.

 

My program starts with a small login screen where user credentials are needed.

When the login is succesful the main form appears.

But the login screen is still visible behind the mainform until the mainform is closed.

How can I close the login screen directly when the main form is showed.

 

                  // SHOW MAIN FORM
                  try
                    mainkForm := Tfrm_Main.Create(Self);
                    try
                      mainkForm.ShowModal;
                    finally
                      mainkForm.Free;
                      Release; // CLOSE CURRENT LOGIN FORM
                    end;
                  except
                    on E: Exception do
                      DoShowException(E);
                  end;

 

[Lajos Juhász 291]

23 minutes ago, Lainkes said:

My program starts with a small login screen where user credentials are needed.

When the login is succesful the main form appears.

But the login screen is still visible behind the mainform until the mainform is closed.

How can I close the login screen directly when the main form is showed.

 

 

You should code this in different way. You can find an example at https://www.thoughtco.com/display-a-login-password-dialog-1058469 unfortunately the code formatting is not correct but you can see the idea.

[Lainkes 0]

I add a screenshot of my form settings.

So it's more clear. (I hope)

[Remy Lebeau 1375]

2 hours ago, Lajos Juhász said:

The correct code would be:

 

// OPEN INPUT SCREEN FOR BOR DOSSIER
                  try
                    inputCheckForm := Tfrm_InputCheck.Create(Self);
                    try
                      inputCheckForm.ShowModal;
                    finally
                      inputCheckForm.Free;
                      Release; // CLOSE THE CURRENT INPUT FORM
                    end;
                  except
                    on E: Exception do
                      DoShowException(E);
                  end;
 

https://docwiki.embarcadero.com/Libraries/Athens/en/Vcl.Forms.TCustomForm.Release

Release() destroys the Form that it is called on. Whereas Close() merely closes (hides) the Form, allowing it to be reopened (shown) again at a later time if desired. 

Edited March 20 by Remy Lebeau

[Lajos Juhász 291]

3 minutes ago, Remy Lebeau said:

Whereas Close() merely closes the Form, allowing it to be reopened at a later time if desired. 

Close can cause access violation if the form is prematurely freed. Release makes sure that every event is finished before the form is freed.

[Remy Lebeau 1375]

5 minutes ago, Lajos Juhász said:

Close can cause access violation if the form is prematurely freed. 

Close() doesn't free the Form unless you explicitly ask for that behavior in its OnClose event (and even that, that logic uses Release() internally).

 

In 20+ years using Delphi, I've never run into an AV from closing a Form. If you are getting an AV when closing a Form then you are likely mismanaging your code that uses the Form.

Edited March 20 by Remy Lebeau

[dummzeuch 1493]

Closing the main form of an application terminates that application and thereby also frees that form and all other forms. The main form of an application is defined as the first form it creates and that cannot be changed easily. So, creating a login form as the first form, has the side effect of terminating the application as soon as it gets closed. which is usually not desirable. Therefore such a login form should never be the first form an application creates.

 

(Unless something has been changed over the years and my experience is outdated (again).)

[Lajos Juhász 291]

15 hours ago, dummzeuch said:

The main form of an application is defined as the first form it creates and that cannot be changed easily.

 

The main form is the first form created using Application.CreateForm you can create forms before using the normal form constructor.

[Stano 143]

I've dealt with this in the dpr unit.
I left things around in the demo as well. Maybe they will inspire you in something

program MyProgram;

{$R *.dres}

uses
  ...
  subBillingRestEnBloc in 'SubForms\Settlement\Edit billing\subBillingRestEnBloc.pas' {frmsubBillingRestEnBloc};

var
  LogonForm: TfrmLoginForm;

{$R *.res}

begin
  ReportMemoryLeaksOnShutDown := True;
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TdtmdBasic, dtmdBasic);
  oAppEnv := TAppEnv.Create;
  Certificate := TCertificate.Create;
  oGlobVar := TGlobalVar.Create(Certificate);

  try
    Licence := TLicence.Create;

    try
      Licence.CheckUp;

      try
        LogonForm := TfrmLoginForm.Create(nil);
      except
        Application.Terminate;
        Exit;
      end;

      if LogonForm.ShowModal = mrOK then
      begin
        FreeAndNil(Licence);
        SupObjJson := TSupObjJson.Create;
        oAppearance := TAppearance.Create(nil);
        oAppearance.ReadOptions;

        if oAppearance.IsTMSStyle then
          oAppearance.SetStylers(oAppearance.StyleName)
        else
        begin

        TStyleManager.TrySetStyle(oAppearance.VclStyle);
          oAppearance.UpdateToolBarPager;
        end;

        IdentificationData := TIdentificationData.Create;

        try
          IdentificationData.Make;
        finally
          FreeAndNil(IdentificationData);
        end;

        Application.CreateForm(TfrmMainFormFOC, frmMainFormFOC);
        frmMainFormFOC.Position := poDesigned;
        SupObjJson.ReadForm(frmMainFormFOC);
        frmMainFormFOC.Show;
        Application.Run;
      end
      else
      begin
        FreeAndNil(LogonForm);
        FreeAndNil(oGlobVar);
        FreeAndNil(oAppEnv);
      end;
    finally
      FreeAndNil(Licence);
    end;
  finally
    FreeAndNil(Certificate);
  end;

end.