Getting location in Blackberry 10

Location awareness is a required feature in most of the mobile phone applications today. Blackberry 10 API provides very easy way of accessing user's current location. In this blog post we will see how applications can access user location through native blackberry 10 API.

Before using Location API you must add following to your .pro file

LIBS += -lQtLocationSubset

To enable your app to obtain the current position or last known position of the device, you must add the access_location_services permission to your bar-descriptor.xml file like this

<permission>access_location_services</permission>

Note that Location services must be enabled on device to get the location.

We use QGeoPositionInfoSource class to find the location of a device and get updates about its position. To use QGeoPositionInfoSource you must include it like this

<QtLocationSubset/QGeoPositionInfoSource>

First we must initialize position source. which can be done through createDefaultSource method of QGeoPositionInfoSource class like this

//Set up the position info source.
QGeoPositionInfoSource *src = QGeoPositionInfoSource::createDefaultSource(this);

There are 3 positioning methods that you can use to find location.

1) All positioning methods (trying GNSS and network methods)
2) Satellite positioning methods (only tries GNSS methods)
3) Non satellite positioning methods (tries WiFi and cell tower positioning methods)

Complete details of these methods can be found here.

By default QGeoPositionInfoSource will have All positioning methods enabled. We can tell it explicitly which method to use by using setPreferredPositioningMethods function. For example if we want to use only Satellite positioning method we can do it like this

src->setPreferredPositioningMethods
(QGeoPositionInfoSource::SatellitePositioningMethods);

We can also specify to use any specific method through setProperty function. For example if we want to use only WiFi method we can do it like this

src->setProperty("provider", "network");
src->setProperty("fixType", "wifi");

We can set many properties of QGeoPositionInfoSource using setProperty method. All details can be found here.

Connecting slots to signals of QGeoPositionInfoSource
We will connect two signals of QGeoPositionInfoSource to our class' slots.

1) positionUpdated (Its emitted when position is found)
2) updateTimeout (Its emitted if timeout occurs in finding a location)

connect(src,SIGNAL(positionUpdated(const QGeoPositionInfo &)),
             this, SLOT(positionUpdated(const QGeoPositionInfo &)));
connect(src,SIGNAL(updateTimeout()),
             this,SLOT(positionUpdateTimedout()));

Sample implementation of positionUpdated slot that handles positionUpdated signal

void MyLocationHandingClass::positionUpdated(
                      const QGeoPositionInfo& geoPositionInfo)
{
    if (geoPositionInfo.isValid())
    {
        QGeoCoordinate geoCoordinate = geoPositionInfo.coordinate();
    qreal latitude = geoCoordinate.latitude();
    qreal longitude = geoCoordinate.longitude();
         //now do something with latitude and longitude
    }
}

You can read about QGeoPositionInfo class here.

Retrieving single fix
To find one time location we use requestUpdate method of QGeoPositionInfoSource, it takes milliseconds as parameter for timeout period.

src->requestUpdates(15000); //request location with 15 secs timeout

Retrieving multiple fixes
To get location at regular intervals we use startUpdates method of QGeoPositionInfoSource. To set interval period we use setUpdateInterval method of QGeoPositionInfoSource which takes milliseconds as parameter.

src->setUpdateInterval(10000); //set interval of 10 seconds
src->startUpdates();

To stop getting location we can use stopUpdates method.

src->stopUpdates();

If you want your app to receive location updates in background (when app is minimized etc). You must set canRunInBackground property to true using setProperty method of QGeoPositionInfoSource.

src->setProperty(“canRunInBackground", true);