Centering the Map to the Phone’s Current Location

The sample’s MapViewModel class contains a GetLocation method that uses the Geolocator class, which is new to Windows Phone 8, to retrieve the phone’s current location (see Listing 18.1).

The GetPositionAsync method is an awaitable method that allows you to retrieve the phone’s last known location without blocking the UI thread.

When attempting to call the Geolocator object’s GetGeopositionAsync method, if location is disabled in the phone’s settings, an UnauthorizedAccessException is raised.

For more information on location tracking and the Geolocator class, see Chapter 17, “Building Location Aware Apps.”

LISTING 18.1. MapViewModel.GetLocation Method

Click here to view code image

async Task<GeoCoordinate> GetLocation()
{
    var geolocator = new Geolocator();
    Geoposition geoposition;

    try
    {
        geoposition = await geolocator.GetGeopositionAsync();
    }
    catch (UnauthorizedAccessException)
    {
        MessageService.ShowMessage(
            "Location is disabled in the phone settings.");
        return center;
    }

    Geocoordinate geocoordinate = geoposition.Coordinate;
    return geocoordinate.ToGeoCoordinate();
}

The MapViewModel class sets its Center property to the value returned by the GetLocation method, as shown:

async void CenterMapOnLocation()
{
    Center = await GetLocation();
    Location = center;
    ZoomLevel = 8;
}

MapView.xaml contains an AppBarIconButton that, when tapped, executes the viewmodel’s CenterMapOnLocationCommand, which calls the CenterMapOnLocation method.