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\":[{},{},{},{},{}] }"

RouteWayPoints list are not serialized properly.

using Android.Gms.Maps.Model;
using Newtonsoft.Json;
using System.Collections.Generic;

namespace App3.Model
{
  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<LatLng> RouteWaypoints { get; set; }
  }
}

Here LatLng is Android.Gms.Maps.Model.LatLng from the Google Maps API for Xamarin.Android.

Serialize command:

string json = JsonConvert.SerializeObject(mapRoute);

to see objects in my list ,click this

You say it isn't serialized correctly - why? Does it throw an exception or just not populate? May be because it's incorrectly serializing the base Java.Lang.Object - could be worth trying to implement a model class and serializing that. — jProg2015
– jProg2015, Commented Jul 21, 2017 at 14:24
That isn't the serialize command you are using, according to your screenshot. You are passing in some JsonSerializerSettings also. What are those settings? Also can you show the code where you set up the waypoints, so we can see what's in them? — Brian Rogers
– Brian Rogers, Commented Jul 21, 2017 at 16:07
@JesusAngulo LatLng is class of the library Android.Gms.Maps.Model i dont write it myself . It contain latitude and longitude of current location. — Hesen Tagiyev
– Hesen Tagiyev, Commented Jul 21, 2017 at 18:58

dbc · Accepted Answer · 2017-07-23 00:18:20Z

2

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());

edited Jul 23, 2017 at 0:18

answered Jul 21, 2017 at 20:33

dbc

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5 Comments

Hesen Tagiyev Over a year ago

i tried your variant of solution first it throw me from debug mode without exception then i made some changes i really dont remember now it loops in

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

method. I stack there link

dbc Over a year ago

@HesenTagiyev - apologies, I answered without unit testing the code. Fixed.

Mick Over a year ago

@HesenTagiyev its a bit rude not marking this as the answer, considering your own answer is entirely based on this one

dbc Over a year ago

@Mick - mine initially had an error, since corrected. HesenTagiyev's answer corrects it also, albeit in a different way.

Hesen Tagiyev Over a year ago

@dbc i especially i emphasize that i found it based your answer. And again thank you for answer , it solved 80% of problem .

Hesen Tagiyev · Accepted Answer · 2017-07-22 21:29:11Z

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);

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