User Login Dialog

An example of user login dialog

This code snippets shows how to implement a simple dialog window that allows the user to enter his username and password in order to make a login attempt. The dialog window will emit a signal in order to notify a listener for the login credentials. The login dialog can also presents a list of usernames to select one from.
The dialog also allows for the proposal of a specified username/password as it could be loaded from a settings or a configuration file.

Header file


#include <QDialog&gt;
#include <QLabel&gt;
#include <QPushButton&gt;
#include <QDialogButtonBox&gt;
#include <QLineEdit&gt;
#include <QComboBox&gt;
#include <QGridLayout&gt;
#include <QStringList&gt;
#include <QDebug&gt;

/*!
Makes class LoginDialog a child to its parent, QDialog
/
class LoginDialog : public QDialog
{
/*!
Turns Login Dialog into a QObject
/
Q_OBJECT

private:
/*!
* A label for the username component.
/
QLabel labelUsername;

/*!
* A label for the password.
/
QLabel labelPassword;

/*!
* An editable combo box for allowing the user
* to enter his username or select it from a list.
/
QComboBox comboUsername;

/*!
* A field to let the user enters his password.
/
QLineEdit editPassword;

/*!
* The standard dialog button box.
/
QDialogButtonBox buttons;

/*!
* A method to set up all dialog components and
* initialize them.
*/
void setUpGUI();

public:
explicit LoginDialog(QWidget parent = 0);
/!
* Sets the proposed username, that can come for instance
* from a shared setting.
username the string that represents the current username
to display
/
void setUsername( QString& username );
/!
* Sets the current password to propose to the user for the login.
* password the password to fill into the dialog form
/
void setPassword( QString& password );
/!
* Sets a list of allowed usernames from which the user
* can pick one if he does not want to directly edit it.
usernames a list of usernames
/
void setUsernamesList( const QStringList& usernames );

signals:

/*!
* A signal emitted when the login is performed.
* username the username entered in the dialog
* password the password entered in the dialog
* index the number of the username selected in the combobox
/
void acceptLogin( QString& username, QString& password, int& indexNumber );
public slots:
/!
* A lot to adjust the emitting of the signal.
*/
void slotAcceptLogin();

};

1. endif // LOGINDIALOG_H

Implementation

LoginDialog::LoginDialog(QWidget parent) :
QDialog(parent)
{
setUpGUI();
setWindowTitle( tr("User Login") );
setModal( true );
}
void LoginDialog::setUpGUI(){
// set up the layout
QGridLayout formGridLayout = new QGridLayout( this );

// initialize the username combo box so that it is editable
comboUsername = new QComboBox( this );
comboUsername->setEditable( true );
// initialize the password field so that it does not echo
// characters
editPassword = new QLineEdit( this );
editPassword->setEchoMode( QLineEdit::Password );

// initialize the labels
labelUsername = new QLabel( this );
labelPassword = new QLabel( this );
labelUsername->setText( tr( "Username" ) );
labelUsername->setBuddy( comboUsername );
labelPassword->setText( tr( "Password" ) );
labelPassword->setBuddy( editPassword );

// initialize buttons
buttons = new QDialogButtonBox( this );
buttons->addButton( QDialogButtonBox::Ok );
buttons->addButton( QDialogButtonBox::Cancel );
buttons->button( QDialogButtonBox::Ok )>setText( tr("Login") );
buttons>button( QDialogButtonBox::Cancel )>setText( tr("Abort") );
// connects slots
connect( buttons>button( QDialogButtonBox::Cancel ),
SIGNAL (clicked()),
this,
SLOT (close())
);

connect( buttons->button( QDialogButtonBox::Ok ),
SIGNAL (clicked()),
this,
SLOT (slotAcceptLogin()) );

// place components into the dialog
formGridLayout->addWidget( labelUsername, 0, 0 );
formGridLayout->addWidget( comboUsername, 0, 1 );
formGridLayout->addWidget( labelPassword, 1, 0 );
formGridLayout->addWidget( editPassword, 1, 1 );
formGridLayout->addWidget( buttons, 2, 0, 1, 2 );

setLayout( formGridLayout );

}

void LoginDialog::setUsername(QString &username){
bool found = false;
for( int i = 0; i < comboUsername->count() && ! found ; i++ )
if( comboUsername->itemText( i ) == username ){
comboUsername->setCurrentIndex( i );
found = true;
}

if( ! found ){
int index = comboUsername->count();
qDebug() << "Select username " << index;
comboUsername->addItem( username );

comboUsername->setCurrentIndex( index );
}

// place the focus on the password field
editPassword->setFocus();
}

void LoginDialog::setPassword(QString &password){
editPassword->setText( password );
}

void LoginDialog::slotAcceptLogin(){
QString username = comboUsername->currentText();
QString password = editPassword->text();
int index = comboUsername->currentIndex();

emit acceptLogin( username, // current username
password, // current password
index // index in the username list
);

// close this dialog
close();
}

void LoginDialog::setUsernamesList(const QStringList &usernames){
comboUsername->addItems( usernames );
}

Usage example

LoginDialog* loginDialog = new LoginDialog( this );
loginDialog->setUsername( "Luca" ); // optional
connect( loginDialog,
SIGNAL (acceptLogin(QString&,QString&,int&)),
this,
SLOT (slotAcceptUserLogin(QString&,QString&)));
loginDialog->exec();