Adding PushPins in Bing Maps

Question

I am trying to add pushpins to a Bing Map. The push pins are got from a JSON feed. I would like to get something like this: enter image description here My code does not work for the first time alone and I cant understand why. My map ViewModel is

public class MapViewModel : INotifyPropertyChanged
{
    public static ObservableCollection<PushpinModel> pushpins = new ObservableCollection<PushpinModel>();
    public static ObservableCollection<PushpinModel> Pushpins 
    {
            get { return pushpins; } 
        set { pushpins = value; } 
    }
}

The Map xaml cs is:

//Map.xaml.cs
public partial class Map : PhoneApplicationPage
{
    #define DEBUG_AGENT
    private IGeoPositionWatcher<GeoCoordinate> watcher;
    private MapViewModel mapViewModel;

    public Map()
    {
        InitializeComponent();
        mapViewModel = new MapViewModel();
        this.DataContext = mapViewModel;
    }

    private void page_Loaded(object sender, RoutedEventArgs e)
    {
        if (watcher == null)
        {

    #if DEBUG_AGENT
            watcher = new Shoporific.My.FakeGPS();
    #else      
            watcher = new GeoCoordinateWatcher(GeoPositionAccuracy.Default);
    #endif
        }
        watcher.Start();

        mapViewModel.Center = watcher.Position.Location;
        PushpinModel myLocation = new PushpinModel() { Location = mapViewModel.Center, Content = "My Location" };
        MapViewModel.Pushpins.Add(myLocation);
        myLocation.RefreshNearbyDeals();
        watcher.Stop();
    }
}

Finally, the PushPinModelClass:

public class PushPinModel
{
    public void RefreshNearbyDeals()
    {
        System.Net.WebClient wc = new WebClient();
        wc.OpenReadCompleted += wc_OpenReadCompleted;
        wc.OpenReadAsync(" a valid uri");
    }

    void wc_OpenReadCompleted(object sender, System.Net.OpenReadCompletedEventArgs e)
    {
        var jsonStream = e.Result;
        DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(Deal[]));
        Deal[] deals = (ser.ReadObject(jsonStream) as Deal[]);

        if (deals.Any())
        {
                var currentLocation = MapViewModel.Pushpins.Where(pin => pin.Content == "My Location");
                MapViewModel.Pushpins = new ObservableCollection<PushpinModel>();
                foreach (var deal in deals)
                    MapViewModel.Pushpins.Add(new PushpinModel()
                    {
                        Content = deal.Store,
                        Location = new GeoCoordinate(deal.Location.Latitude, deal.Location.Longtitude),
                        Offers = deal.Offers,
                    });

        }
    }
}

I am a bit confused that the Pushpins except "My Location" dont show up only on the first time. They appear as expected the second time onwards(If I navigate back and then move to the Map screen again).

A quick tip for you, with the WP7.1 tools the emulator has a GPS simulator. You don't need your Shoporific.My.FakeGPS class. — ColinE
– ColinE, Commented Feb 11, 2012 at 7:29
Yeah, @ColinE: I knew about that. But I wanted the fake GPS even when debugger was not attached. Notice the #def DEBUG_AGENT? I needed this to ensure that the map will centre around jacobs & Javits center. I am doing this as a prototype. — gprasant
– gprasant, Commented Feb 13, 2012 at 4:32

Bryan Watts · Accepted Answer · 2012-02-11 19:52:04Z

1

Inside wc_OpenReadCompleted, you are re-instantiating MapViewModel.Pushpins.

Only call the constructor to an ObservableCollection once (in your case within the MainViewModel). Calling it again messes up the binding that I assume you have in your xaml page.

I believe that you should either remove that line in the PushpinViewModel or call MainViewModel.Pushpins.Clear() instead (depending on what you are trying to accomplish).

answered Feb 11, 2012 at 19:52

Bryan Watts

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