Location Services

An example

The Whereabouts Sample Plugin demonstrates the integration of a custom Whereabouts plugin. The examples/sampleplugin/locationplugin directory contains the plugin, and examples/sampleplugin/mylocationapp contains an application that uses the plugin to retrieve location updates.

First, we create a QWhereabouts subclass called LocationProvider:

    class LocationProvider : public QWhereabouts
    {
        Q_OBJECT
    public:
        LocationProvider(QObject *parent = 0);

        void requestUpdate();
        void startUpdates();
        void stopUpdates();

    private:
        QTimer *m_timer;
    };

This LocationProvider class simply produces updates with the current date/time and latitude-longitude coordinates of (0, 0). It uses QTimer to implement timed updates for QWhereabouts::startUpdates() and QWhereabouts::stopUpdates(). Here is the implementation:

    LocationProvider::LocationProvider(QObject *parent)
        : QWhereabouts(QWhereabouts::TerminalBasedUpdate, parent),
          m_timer(new QTimer(this))
    {
        connect(m_timer, SIGNAL(timeout()), SLOT(requestUpdate()));
    }

    void LocationProvider::requestUpdate()
    {
        QWhereaboutsUpdate update;
        update.setCoordinate(QWhereaboutsCoordinate(0.0, 0.0));
        update.setUpdateDateTime(QDateTime::currentDateTime());
        emitUpdated(update);
    }

    void LocationProvider::startUpdates()
    {
        if (updateInterval() > 0)
            m_timer->start(updateInterval());
        else
            m_timer->start(1000);
    }

    void LocationProvider::stopUpdates()
    {
        m_timer->stop();
    }

Then we create a Whereaboutsplugin called LocationPlugin that is able to create and return instances of LocationProvider. Here is the class definition:

    class QTOPIA_PLUGIN_EXPORT LocationPlugin : public QWhereaboutsPlugin
    {
        Q_OBJECT
    public:
        LocationPlugin(QObject *parent = 0);

        QWhereabouts *create(const QString &source);
    };

In the locationplugin.cpp file, we implement create() to return an instance of LocationProvider, and export the plugin using the QTOPIA_EXPORT_PLUGIN macro:

    LocationPlugin::LocationPlugin(QObject *parent)
        : QWhereaboutsPlugin(parent)
    {
    }

    QWhereabouts *LocationPlugin::create(const QString &source)
    {
        Q_UNUSED(source);
        return new LocationProvider;
    }

    QTOPIA_EXPORT_PLUGIN(LocationPlugin)

Then, once the plugin has been installed with qbuild image, you can use it by passing the class name to QWhereaboutsFactory::create(). (The class name argument is not case-sensitive.) So in the examples/sampleplugin/mylocationapp project, we create a MyLocationApp class that uses our custom plugin, like this:

    MyLocationApp::MyLocationApp(QWidget *parent, Qt::WFlags flags)
        : QMainWindow(parent, flags)
    {
        QWhereabouts *whereabouts = QWhereaboutsFactory::create("locationplugin");
        connect(whereabouts, SIGNAL(updated(QWhereaboutsUpdate)),
                SLOT(updated(QWhereaboutsUpdate)));

        whereabouts->startUpdates();
    }

    void MyLocationApp::updated(const QWhereaboutsUpdate &update)
    {
        // Respond to update here
    }

So MyLocationApp now receives updates through the LocationProvider we created.

To make this the default plugin to be returned if QWhereaboutsFactory::create() is called without any arguments, set the "Plugins/Default" value in $QPEDIR/etc/Settings/Trolltech/Whereabouts.conf to "locationplugin".

Other examples

The Whereabouts Mapping Demo uses the Whereabouts API together with Google Maps to either track the user's current location, or provide a simulation of a previous journey using a NMEA data log.