User Login Dialog

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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

  1. include <QDialog>
  2. include <QLabel>
  3. include <QPushButton>
  4. include <QDialogButtonBox>
  5. include <QLineEdit>
  6. include <QComboBox>
  7. include <QGridLayout>
  8. include <QStringList>
  9. include <QDebug>

/*!

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();