How to Make a Delphi Login Form

How to Make a Delphi Login Form The MainForm of a Delphi application is a form (window) that is the first one created in the main body of the application. If you need to implement some kind of authorization for your Delphi application, you might want to display a login/password dialog before the main form is created and displayed to the user. In short, the idea is to  create, display, and destroy the login dialog before creating the main form. The Delphi MainForm When a new Delphi project is created, Form1 automatically becomes the value of the MainForm property (of the global Application object). To assign a different form to the MainForm property, use the Forms page of the Project Options dialog box at design time. When the main form closes, the application terminates. Login/Password Dialog Lets start by creating the main form of the application. Create a new Delphi project containing one form. This form is, by design, the main form. If you change the name of the form to TMainForm and save the unit as main.pas, the projects source code looks like this (the project was saved as PasswordApp): program PasswordApp; uses Forms, main in main.pas {MainForm}; {$R *.res} begin Application.Initialize; Application.CreateForm(TMainForm, MainForm) ; Application.Run; end. Now, add a second form to the project. By design, the second form thats added gets listed in the Auto-Create Forms list on the Project Options dialog. Name the second form TLoginForm and remove it  from the Auto-Create Forms list. Save the unit as login.pas. Add a Label, Edit, and Button on the form, followed by a class method to create, show, and close the login/password dialog. The method Execute returns true if the user has entered the correct text in the password box. Heres the full source code: unit login; interface uses Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls; type TLoginForm class(TForm) LogInButton: TButton;pwdLabel: TLabel;passwordEdit: TEdit;procedure LogInButtonClick(Sender: TObject) ; publicclass function Execute : boolean;end; implementation{$R *.dfm} class function TLoginForm.Execute: boolean;beginwith TLoginForm.Create(nil) dotry Result : ShowModal mrOk; finally Free; end;end; procedure TLoginForm.LogInButtonClick(Sender: TObject) ;beginif passwordEdit.Text delphi then ModalResult : mrOK else ModalResult : mrAbort; end; end. The Execute method dynamically creates an instance of the TLoginForm and displays it using the ShowModal method. ShowModal does not return until the form closes. When the form closes, it returns the value of the ModalResult property. The LogInButton OnClick event handler assigns mrOk to the ModalResult property if the user has entered the correct password (which is delphi in the above example). If the user has provided a wrong password, ModalResult is set to mrAbort (it can be anything except mrNone). Setting a value to the ModalResult property closes the form. Execute returns true if ModalResult equals mrOk (if the user has entered the correct password). Don't Create MainForm Before Login You now only need to make sure the main form is not created if the user failed to provide the correct password. Heres how the projects source code should look: program PasswordApp; uses Forms, main in main.pas {MainForm}, login in login.pas {LoginForm}; {$R *.res} beginif TLoginForm.Execute thenbegin Application.Initialize; Application.CreateForm(TMainForm, MainForm) ; Application.Run; endelsebegin Application.MessageBox(You are not authorized to use the application. The password is delphi., Password Protected Delphi application) ; end;end. Note the usage of the if then else block to determine if the main form should be created. If Execute returns false, MainForm is not created and the application terminates without starting.