Qt Extended Phone Library

Implementing Telephony Interfaces

Telephony services implement interfaces by inheriting from the client-side class and overriding its public slots with a new implementation. To demonstrate how this works, we will implement the hypothetical "SMS over SIP" referred to in the previous section.

    class VoIPSMSSender : public QSMSSender
    {
        Q_OBJECT
    public:
        VoIPSMSSender( QObject *parent = 0 )
            : QSMSSender( "voip", parent, QCommInterface::Server ) {}
        ~VoIPSMSSender() {}

    public slots:
        void send( const QString& id, const QSMSMessage& msg );
    };

    void VoIPSMSSender::send( const QString& id, const QSMSMessage& msg )
    {
        ...
    }

The VoIP service creates an instance of VoIPSMSSender, passing the QCommInterface::Server flag to the base class constructor. This tells the Qt Extended Phone Library to advertise VoIPSMSSender as the implementation of the interface QSMSSender for the service voip. The Qt Extended Phone Library uses Qt Extended IPC and the Value Space to effect communication between the client application and the service. There is more information on how this process works in the documentation for QAbstractIpcInterface, which is the base class for all telephony interfaces.

The VoIPSMSSender instance can be created anywhere in the system, usually in the daemon that implements the VoIP telephony service. The example VoIP implementation that comes with Qt Extended is implemented by the sipagent daemon.

Telephony services do not need to be part of the qpe process, or any other special Qt Extended application, although they can be. The default implementation of the GSM modem service is created by qpe, but other modem implementations could be in separate daemons.

Most telephony services will have more than one interface. The QTelephonyService class makes it easy to create large numbers of related interfaces within a service. Our VoIP implementation would look something like this:

    class VoIPService : public QTelephonyService
    {
        Q_OBJECT
    public:
        VoIPService( QObject *parent = 0 )
            : QTelephonyService( "voip", parent ) {}
        ~VoIPService() {}

        void initialize();
    };

    void VoIPService::initialize()
    {
        if ( !supports<QSMSSender>() )
            addInterface( new VoIPSMSSender( this ) );

        ...

        QTelephonyService::initialize();
    }

The VoIP daemon creates an instance of VoIPService, and then calls the initialize() method to complete the initialization process.

In the example above, we call supports() to first check if there is an existing implementation of QSMSSender before creating the new one. This style of interface creation supports inheritance of services. A better version of the VoIP service could inherit from VoIPService, override initialize(), and create a new implementation of the QSMSSender interface that replaces the original.

The VoIP Integration Guide provides more detailed information on integrating VoIP telephony services into Qt Extended, and the particular interfaces that are required.

    [Extensions]
    [Standard]
    Version = 100

    QtopiaApplication::instance()->registerRunningTask( "Telephony", obj );