var serviceObj = null;
var criteria = null;
 
window.onload = init;
 
// Initializes the widget
function init() {
    // Obtain the Location service object
    try {
        serviceObj = device.getServiceObject("Service.Location", "ILocation");
    } catch (ex) {
        alert("Service object cannot be found.");
        return;
    }
 
    // Initialize the criteria for the service object
    criteria = new Object();
    criteria.LocationInformationClass = "BasicLocationInformation";
}
 
// Starts the tracking
function startTracking() {
    if (serviceObj == null) {
        alert("Service object has not been initialized.");
        return;
    }
 
    try {
        // Define the callback function for tracking the location
        var result = serviceObj.ILocation.Trace(criteria, locationDataReady);
    } catch (ex) {
        alert(ex);
    }
}
 
// Called when Trace has got data
function locationDataReady(transId, eventCode, result) {
    // On error situation, display the error message
    if (eventCode == 4) {
        alert("Error " + result.ErrorCode + ": " + result.ErrorMessage);
        return;
    }
 
    var latitude = result.ReturnValue.Latitude;
    displayData("latitudeData", latitude.toFixed(4) + " \u00B0");
 
    var longitude = result.ReturnValue.Longitude;
    displayData("longitudeData", longitude.toFixed(4) + " \u00B0");
}
 
// Displays the data in an HTML element
function displayData(elementId, data) {
    var element = document.getElementById(elementId);
 
    // Remove the first child node, if it's not null
    if (element.firstChild != null) {
        element.removeChild(element.firstChild);
    }
 
    element.appendChild(document.createTextNode(data));
}