QNetworkSession Class Reference
[QtNetwork module]

void QNetworkSession::preferredConfigurationChanged ( const QNetworkConfiguration & config, bool isSeamless )   [signal]

This signal is emitted when the preferred configuration/access point for the session changes. Only sessions which are based on service network configurations may emit this signal. config can be used to determine access point specific details such as proxy settings and isSeamless indicates whether roaming will break the sessions IP address.

As a consequence to this signal the application may start the roaming process by calling migrate() or may chose to ignore() the new access point. If the application doesn't call either of the two functions the session ignores the migration opportunity.

If the roaming process is non-seamless the IP address will change which means that a socket becomes invalid. However seamless mobility can ensure that the local IP address does not change. This is achieved by using a virtual IP address which is bound to the actual link address. During the roaming process the virtual address is attached to the new link address.

Some platforms may support the concept of Forced Roaming and Application Level Roaming (ALR). Forced roaming implies that the platform may simply roam to a new configuration without consulting applications. It is up to the application to detect the link layer loss and reestablish its sockets. In contrast ALR provides the opportunity to prevent the system from roaming. If this session is based on a configuration that supports roaming the application can choose whether it wants to be consulted (ALR use case) by connecting to this signal. For as long as this signal connection remains the session remains registered as a roaming stakeholder; otherwise roaming will be enforced by the platform.

See also migrate(), ignore(), and QNetworkConfiguration::isRoamingAvailable().

    QNetworkConfigurationManager mgr;
    QNetworkConfiguration ap = mgr.defaultConfiguration();
    QNetworkSession* session = new QNetworkSession(ap);
    ... //code activates session

    QString ident = session->sessionProperty("ActiveConfigurationIdentifier").toString();
    if ( ap.type() == QNetworkConfiguration::ServiceNetwork ) {
        Q_ASSERT( ap.identifier() != ident );
        Q_ASSERT( ap.children().contains( mgr.configurationFromIdentifier(ident) ) );
    } else if ( ap.type() == QNetworkConfiguration::InternetAccessPoint ) {
        Q_ASSERT( ap.identifier() == ident );
    }

    session->open();
    if (session->waitForOpened(1000))
        qDebug("Open!");