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
// 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 RouteWaypoints { get; set; }
}

Then, construct your MapRoute as follows:

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