получение Null Reference Exception в то время как callBack в ответе от 'GeoCodeService', используя Bing Maps в приложении Windows Phone 7.1

Question

Я разрабатываю приложение для Windows Phone, в котором мне нужно показать карты для определения местоположения двух разных мест и показать маршрут между этими двумя точками, а также направления. Получаю адресную строку TO и FROM от веб-службы json, которую мне нужно использовать для отправки запроса местоположений в GeoCodeService.

Для достижения вышеуказанного я использую Bing Maps - «GeoCodeService», «GeoRouteService» и пытаюсь использовать следующий код. Во время работы приложения я получаю NullReferenceException при получении ответа на callBack от GeoCodeService.

Поскольку я совершенно новичок в разработке приложений для Windows Phone, я не использую полный шаблон MVVM. Однако я мог получить данные из веб-службы Json, но затем не смог получить результат от GeoCodeService, чтобы связать их с моей картой.

Вот мой код xaml:

<controls:PivotItem Header="Map">
    <StackPanel Orientation="Vertical">
        <maps:Map x:Name="bingMap"
                  Center="50.851041,4.361572"
                  ZoomLevel="10"
                  CredentialsProvider="{StaticResource MapCredentials}">
            <maps:MapPolyline Locations="{Binding RoutePoints, Converter={StaticResource locationConverter}}"
                  Stroke="#FF0000FF"
                  StrokeThickness="5" />
            <maps:Pushpin Location="{Binding StartPoint, Converter={StaticResource locationConverter}}"
                  Content="Start" />
            <maps:Pushpin Location="{Binding EndPoint, Converter={StaticResource locationConverter}}"
                  Content="End" />
        </maps:Map>
        <StackPanel Orientation="Horizontal"
                    VerticalAlignment="Bottom">
            <Button Margin="80,0,0,0"
                    x:Name="btnputodo"
                    Click="btnputodo_Click"
                    HorizontalAlignment="Left"
                    FontFamily="Verdana"
                    FontSize="18"
                    VerticalAlignment="Bottom"
                    BorderBrush="Transparent"
                    Height="60"
                    Content="Pu to Do"
                    Width="150"
                    Background="White"
                    Foreground="Black"/>
            <Button x:Name="btnmyloctopu"
                    Click="btnmyloctopu_Click"
                    HorizontalAlignment="Left"
                    FontFamily="Verdana"
                    FontSize="18"
                    VerticalAlignment="Bottom"
                    BorderBrush="Transparent"
                    Height="60"
                    Content="Loc to Pu"
                    Width="150"
                    Background="White"
                    Foreground="Black"/>
        </StackPanel>
    </StackPanel>
</controls:PivotItem>
<controls:PivotItem Header="Directions">
    <ListBox ItemsSource="{Binding Itinerary, Converter={StaticResource itineraryConverter}}"
             Grid.RowSpan="2"
             ItemTemplate="{StaticResource ItineraryItemComplete}" />
</controls:PivotItem>

Ниже приведен мой код xaml.cs (код позади):

private Location toLocation;

private Location fromLocation;

private Address from;
public Address From
{
    get { return from; }
    set
    {
        from = value;
        Change("From");
    }
}

private Address to;
public Address To
{
    get { return to; }
    set
    {
        to = value;
        Change("To");
    }
}
private Location startPoint;
public Location StartPoint
{
    get { return startPoint; }
    set
    {
        startPoint = value;
        Change("StartPoint");
    }
}

private Location endPoint;
public Location EndPoint
{
    get { return endPoint; }
    set
    {
        endPoint = value;
        Change("EndPoint");
    }
}

private ObservableCollection<Location> routePoints;
public ObservableCollection<Location> RoutePoints
{
    get { return routePoints; }
    set
    {
        routePoints = value;
        Change("RoutePoints");
    }
}

private ObservableCollection<ItineraryItem> itinerary;
public ObservableCollection<ItineraryItem> Itinerary
{
    get
    {
        return itinerary;
    }
    set
    {
        itinerary = value;
        Change("Itinerary");
    }
}
public event PropertyChangedEventHandler PropertyChanged;

private void Change(string property)
{
    if (PropertyChanged != null)
        PropertyChanged(this, new PropertyChangedEventArgs(property));
}

public event EventHandler RouteResolved;

private void RaiseRouteResolved()
{
    if (RouteResolved != null)
        RouteResolved(this, EventArgs.Empty);
}

private void btnputodo_Click(object sender, RoutedEventArgs e)
{

    foreach (var dictionary in pickdrops)
    {
        if (dictionary.Key == "pickups")
        {
            locate = dictionary.Value;
            this.From = new Address();
            this.From.AddressLine = locate;
            this.From.Locality = this.From.AdminDistrict = this.From.CountryRegion = this.From.District = this.From.PostalCode = this.From.PostalTown = string.Empty;
            ResolveRoute();

        }
        if (dictionary.Key == "drops")
        {
            locate = dictionary.Value;
            this.To= new Address();
            this.To.AddressLine = locate;
            this.To.Locality = this.To.AdminDistrict = this.To.CountryRegion = this.To.District = this.To.PostalCode = this.To.PostalTown = string.Empty;
            ResolveRoute1();

        }
    }
}


public void ResolveRoute()
{
    GetGeoLocation(From, (l) => fromLocation = l);

}

public void ResolveRoute1()
{
    GetGeoLocation1(To, (l) => toLocation = l);
}

private void GetGeoLocation1(Address address, Action<Utils.WP7.Bing.BingGeo.GeocodeLocation> callBack)
{
    var geoRequest = new GeocodeRequest();
    geoRequest.Credentials = new Credentials();
    geoRequest.Credentials.ApplicationId = App.BingApiKey;
    geoRequest.Address = address;

        var geoClient = new GeocodeServiceClient("BasicHttpBinding_IGeocodeService");
    geoClient.GeocodeCompleted += (s, e) =>
    {
        string statusCode =  e.Result.ResponseSummary.StatusCode.ToString();
        string ss = e.Result.Results == null ? "EMPTY" : "OK";
        if (e.Result.Results != null && e.Result.Results.Count > 0)
        {
            string dd = e.Result.Results[0].Locations[0].Latitude.ToString(); 
        }

        // Am getting Exception at the below statement -->
        callBack(e.Result.Results.FirstOrDefault().Locations.FirstOrDefault());
        // <---

        LocationLoaded();
    };
    geoClient.GeocodeAsync(geoRequest);
}

private void GetGeoLocation(Address address, Action<Utils.WP7.Bing.BingGeo.GeocodeLocation> callBack)
{
    var geoRequest = new GeocodeRequest();
    geoRequest.Credentials = new Credentials();
    geoRequest.Credentials.ApplicationId = App.BingApiKey;
    geoRequest.Address  = address;


    var geoClient = new GeocodeServiceClient("BasicHttpBinding_IGeocodeService");
    geoClient.GeocodeCompleted += (s, e) =>
    {
        callBack(e.Result.Results.FirstOrDefault().Locations.FirstOrDefault());
        LocationLoaded();
    };
    geoClient.GeocodeAsync(geoRequest);
}


private void LocationLoaded()
{
    if (fromLocation != null && toLocation != null)
    {
        var fromWaypoint = new Waypoint();
        fromWaypoint.Description = "From";
        fromWaypoint.Location = new Microsoft.Phone.Controls.Maps.Platform.Location();
        fromWaypoint.Location.Altitude = fromLocation.Altitude;
        fromWaypoint.Location.Latitude = fromLocation.Latitude;
        fromWaypoint.Location.Longitude = fromLocation.Longitude;

        var toWaypoint = new Waypoint();
        toWaypoint.Description = "To";
        toWaypoint.Location = new Microsoft.Phone.Controls.Maps.Platform.Location();
        toWaypoint.Location.Altitude = toLocation.Altitude;
        toWaypoint.Location.Latitude = toLocation.Latitude;
        toWaypoint.Location.Longitude = toLocation.Longitude;

        var routeRequest = new RouteRequest();
        routeRequest.Credentials = new Microsoft.Phone.Controls.Maps.Credentials();
        routeRequest.Credentials.ApplicationId = App.BingApiKey;
        routeRequest.Waypoints = new System.Collections.ObjectModel.ObservableCollection<Waypoint>();
        routeRequest.Waypoints.Add(fromWaypoint);
        routeRequest.Waypoints.Add(toWaypoint);
        routeRequest.Options = new RouteOptions();
        routeRequest.Options.RoutePathType = RoutePathType.Points;
        routeRequest.UserProfile = new Utils.WP7.Bing.BingRoute.UserProfile();
        routeRequest.UserProfile.DistanceUnit = Utils.WP7.Bing.BingRoute.DistanceUnit.Kilometer;

        var routeClient = new RouteServiceClient("BasicHttpBinding_IRouteService");
        routeClient.CalculateRouteCompleted += new EventHandler<CalculateRouteCompletedEventArgs>(OnRouteComplete);
        routeClient.CalculateRouteAsync(routeRequest);
    }
}

private void OnRouteComplete(object sender, CalculateRouteCompletedEventArgs e)
{
    if (e.Result != null && e.Result.Result != null && e.Result.Result.Legs != null & e.Result.Result.Legs.Any())
    {
        var result = e.Result.Result;
        var legs = result.Legs.FirstOrDefault();

        StartPoint = legs.ActualStart;
        EndPoint = legs.ActualEnd;
        RoutePoints = result.RoutePath.Points;
        Itinerary = legs.Itinerary;


    }
}

Answer 1

Я думаю, что ваша проблема связана с тем, как вы извлекаете данные результатов из вашего запроса.

Прежде всего, я вижу, что вы проверяете, являются ли ваши параметры NULL значениями таким образом:

if (e.Result.Results != null && e.Result.Results.Count > 0)
    (... some logic here ...)

Но я думаю, что лучше сделать это:

 if(e.Error == null)
     // HERE YOU'D WANT TO MANAGE A REQUEST EXCEPTION
     // (FOR EXAMPLE AN UNPREDICTABLE PROBLEM OF THE BING WEB SERVICE!)
     // e.Error is an Exception class
 else
 {
     // Get the first result received:
     var geoResult = (from r in e.Result.Results
                     orderby (int)r.Confidence ascending // USE THIS CLAUSE TO SORT THE RESULT BY CONFIDENCE, OTHERWISE REMOVE IT!
                     select r).FirstOrDefault();

     // DO I HAVE A VALID RESULT?
     if (geoResult != null)
     {
         // I DO HAVE A VALID RESULT FOR GEOCODING!!

         // Defined a new point location for storing my information:
         Location currentLocation = new Location();

         // Set the coordinates:
         currentLocation.Latitude = geoResult.Locations[0].Latitude;
         currentLocation.Longitude = geoResult.Locations[0].Longitude;

         // Your problem was here:
         callBack(currentLocation.Locations[0]);

         // ...NEXT SOME SAMPLE CODE...

         // Set the point on the Bing map with a certain level of zoom:
         GeoLocationMap.SetView(currentLocation, 10);

         // Set the location of the visual pin on the map!
         GeoLocationMapPushpin.Location = currentLocation;
     }
 }

Надеюсь, это поможет!