输入字符串格式错误创建markerOption

Question

我在下面的代码中遇到错误（System.FormatException：输入字符串的格式不正确。），为什么。我的代码工作正常，但现在我不知道为什么。  我正试图从地图上的json获取坐标

public void initializeMap(String content)
    {
        LatLng location = new LatLng(codecLatitude, codecLongitude);  // setting latitude and longitude
                                                                      // getting MapFragment
        mapFragment = (MapFragment)FragmentManager.FindFragmentById(Resource.Id.map);
        // setting MapFragment to googleMap variable
        google = mapFragment.Map;


        if (google != null)
        {
            google.MapType = GoogleMap.MapTypeNormal;  // setting map type

            // creating marker
            try
            {
                JSONArray json = new JSONArray(content);
                for (int i = 0; i < json.Length(); i++)
                {
                    JSONObject obj = json.GetJSONObject(i);
                    String lati = obj.GetString("latitude");
                    String longi = obj.GetString("longitude");
                    String full = obj.GetString("fullname");
                    String mobi = obj.GetString("mobile");
                    String id = obj.GetString("driver_id");
                    String token = obj.GetString("token");
                    String cartype = obj.GetString("car_type");
                   MarkerOptions marker = new MarkerOptions()
                        .SetPosition(new LatLng(Double.Parse(lati), Double.Parse(longi)))
                        .SetTitle(full)
                    .SetSnippet(mobi);
                    if (cartype == "ركشة")
                    {


                        marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.iconreksha));
                    }
                    else
                    {
                        marker.SetIcon(BitmapDescriptorFactory.FromResource(Resource.Drawable.carmark));

                    }
                    google.AddMarker(marker);    // add marker to google Map

错误消息指示器指向以下行

   MarkerOptions marker = new MarkerOptions()
                        .SetPosition(new LatLng(Double.Parse(lati), Double.Parse(longi)))
                        .SetTitle(full)
                    .SetSnippet(mobi);