无法在MapControl上绘制路线（Windows Phone 8.1）

Question

我需要在MapControl的两点之间绘制一条行车路线（我正在为Windows Phone 8.1做这个）。我使用MSDN的教程做了一切，但它不起作用 - 路由是空的。我究竟做错了什么？这是代码。

BasicGeoposition startLocation = new BasicGeoposition();
startLocation.Latitude = 40.7517;
startLocation.Longitude = -073.9766;
Geopoint startPoint = new Geopoint(startLocation);

// End at Central Park in New York City.
BasicGeoposition endLocation = new BasicGeoposition();
endLocation.Latitude = 40.7669;
endLocation.Longitude = -073.9790;
Geopoint endPoint = new Geopoint(endLocation);

// Get the route between the points.
MapRouteFinderResult routeResult =
    await MapRouteFinder.GetDrivingRouteAsync(
    startPoint,
    endPoint,
    MapRouteOptimization.Time,
    MapRouteRestrictions.None,
    290
    );


MapRouteView viewOfRoute = new MapRouteView(routeResult.Route);
viewOfRoute.RouteColor = Colors.Blue;
viewOfRoute.OutlineColor = Colors.Blue;

// Add the new MapRouteView to the Routes collection
// of the MapControl.
mapeczka.Routes.Add(viewOfRoute);

// Fit the MapControl to the route.
await mapeczka.TrySetViewBoundsAsync(
    routeResult.Route.BoundingBox,
    null,
    Windows.UI.Xaml.Controls.Maps.MapAnimationKind.Bow);

if (routeResult.Status == MapRouteFinderStatus.Success)
{
    // Use the route to initialize a MapRouteView.
    viewOfRoute = new MapRouteView(routeResult.Route);
    viewOfRoute.RouteColor = Colors.Yellow;
    viewOfRoute.OutlineColor = Colors.Black;

    // Add the new MapRouteView to the Routes collection
    // of the MapControl.

}
mapeczka.Routes.Add(viewOfRoute);
// Fit the MapControl to the route.
await mapeczka.TrySetViewBoundsAsync(
    routeResult.Route.BoundingBox,
    null,
    Windows.UI.Xaml.Controls.Maps.MapAnimationKind.None);