Json.NET returns empty objects serializing list of Android.Gms.Maps.Model.LatLng objects

Question

While serializing MapRoute object I got JSON data like this:

\"{\\\"RouteName\\\":\\\"route1\\\",\\\"RouteWaypoints\\\":[{},

Answer 1

I believe Android.Gms.Maps.Model.LatLng is actually a Managed Callable Wrapper proxy for Google APIs for Android's LatLng. Possibly (I cannot test it myself) Json.NET's reflection mechanism is unable to successfully discover the members of such a wrapper type.

If so, the easiest workaround would be to introduce a Data Transfer Object, map the LatLng to the DTO, and serialize that. First, define your types as follows:

// Required for For System.Linq.Enumerable.Select<TSource,TResult>
// https://developer.xamarin.com/api/member/System.Linq.Enumerable.Select%7BTSource,TResult%7D/p/System.Collections.Generic.IEnumerable%7BTSource%7D/System.Func%7BTSource,TResult%7D/
using System.Linq;  

public class LatLngDTO
{
    public double Latitude { get; set; }
    public double Longitude { get; set; }

    public static implicit operator LatLng(LatLngDTO latLng)
    {
        if (latLng == null)
            return null;
        return new LatLng(latLng.Latitude, latLng.Longitude);
    }

    public static implicit operator LatLngDTO(LatLng latLng)
    {
        if (latLng == null)
            return null;
        return new LatLngDTO { Latitude = latLng.Latitude, Longitude = latLng.Longitude };
    }
}

public class Id
{
    [JsonProperty(PropertyName = "$oid")]
    public string id { get; set; }
}

public class MapRoute
{
    public Id _id { get; set; }
    public string RouteName { get; set; }
    public List<LatLngDTO> RouteWaypoints { get; set; }
}

Then, construct your MapRoute as follows:

_mapRoute.RouteWaypoints = (_wayPoints == null ? null : _wayPoints.Select(l => (LatLngDTO)l).ToList());

Answer 2

i modified @dbc LatLngDTO class and write two static object returner methods like below:

using Android.Gms.Maps.Model;

     namespace App3.Model
     {
        public class LatLngDTO
        {
          public double Latitude { get; set; }
          public double Longitude { get; set; }

          public LatLngDTO(double lat,double lng)
          {
            Latitude = lat;
            Longitude = lng;
           }

           public static LatLng ToLatLng(LatLngDTO latLng)
           {
             if (latLng == null)
                return null;
             else
                return new LatLng(latLng.Latitude, latLng.Longitude);
            }

            public static LatLngDTO ToLatLngDTO(LatLng latLng)
            {
              if (latLng == null)
                return null;
              else
                return new LatLngDTO(latLng.Latitude, latLng.Longitude);
            }
        }

it solved my issue. And i serialized my model with list of LatLngDTO objects like below:

mapRoute.RouteWaypoints = (_wayPoints == null ? null : _wayPoints.Select(l => LatLngDTO.ToLatLngDTO(l)).ToList());

            string json = JsonConvert.SerializeObject(mapRoute);
            Json = json;
            http.PostHTTPData(urlString, json);