MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

(string), and timestamp (Date) properties, if the geolocation provider supplies such data. 51
You can indicate the accuracy you’re looking for through the Geolocator’s desiredAccuracy
property, which is either PositionAccuracy.default or PositionAccuracy.high. The latter, mind you,
will be much more radio or network intensive. This might incur higher costs on metered broadband
connections and can shorten battery life, so set this to high only if it’s essential to your user experience.
The Geolocator also provides a locationStatus property, which is a PositionStatus object
containing ready, initializing, noData, disabled, notInitialized, and notAvailable. It should be
obvious that you can’t get data from a Geolocator that’s in any state other than ready. To track this, you
can listen to the Geolocator’s statusChanged event, where eventArgs.status property in your handler
will contain a PositionStatus; this is helpful when you find that a GPS device might take a couple
seconds to provide a reading. For an example of using this event, see Scenario 1 of the Geolocation
sample in the Windows SDK:
geolocator = new Windows.Devices.Geolocation.Geolocator();
geolocator.addEventListener("statuschanged", onStatusChanged); //Remember to remove later
function onStatusChanged(e) {
switch (e.status) {
// ...
}
}
Note that PositionStatus and statusChanged reflect the readiness of the GPS device, and that
readiness is not affected by the Location permission in the app’s Settings pane. As demonstrated in Here
My Am!, an app needs to check permissions by trying to obtain a setting, which is a different concern
from device readiness.
The other two interesting properties of the Geolocator are movementThreshold, a distance in meters
that the device can move before another reading is triggered (which can be used for geo-fencing
scenarios), and reportInterval, which is the number of milliseconds between attempted readings. Be
conservative with the latter, setting it to what you really need, because you again want to minimize
network or radio activity. In any case, when the Geolocator takes and other reading and finds that the
device has moved beyond the movement-Threshold, it will fire a positionChanged event, where the
eventArgs.position property is a new Geoposition object. This is also shown in Scenario 1 of the
Geolocation sample:
geolocator.addEventListener("positionchanged", onPositionChanged);
function onPositionChanged(e) {
var coord = e.position.coordinate;
document.getElementById("latitude").innerHTML = coord.latitude;
document.getElementById("longitude").innerHTML = coord.longitude;
51 That is, the civicAddress property might not be available or might be empty. An alternate means to obtain it is to use the
Bing Maps API, specifically the MapAddress class, to convert coordinates into an address.
399