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无法将JValue转换为JObject

c#asp.netjsonjson.net
3
我有一个包含静态方法的类，如下所示：
public static class RouteSerializer
{
    public static string SerializeRouteInformation(string content)
    {
        RouteMapModel routeMapModel = new RouteMapModel();
        List<RouteMapModel.end_location> endLocationList = new List<RouteMapModel.end_location>();

        var obj = JObject.Parse(content);

        string objRoutes = obj["routes"].ToString();

        JArray routeArray = JArray.Parse(objRoutes);

        JArray legArray = new JArray();
        foreach (JObject item in routeArray)
        {
            string leg = item.GetValue("legs").ToString();                
            legArray.Add(leg);
        }

        JArray stepArray = new JArray();
        foreach (JObject item in legArray)
        {
            string step = item.GetValue("steps").ToString();
            stepArray.Add(step);
        }

        foreach(JObject item in stepArray)
        {
            string endLocation = item.GetValue("end_location").ToString();
            var serializedEndLocation = JsonConvert.DeserializeObject<RouteMapModel.end_location>(endLocation);
            endLocationList.Add(serializedEndLocation);
        }

        //... goes on
    }
}

但是，在第二个foreach的开头，我遇到了一个错误，它说Newtonsoft.Json.Linq.JValue不能赋值给Newtonsoft.Json.Linq.JObject。但问题是，如果我在后面的foreach子句中将项目类型从JObject更改为JValue，我就无法使用.GetValue()方法，因为JValue不包含此方法。
以下是我正在处理的JSON字符串：
    { "geocoded_waypoints" : [
      {
         "geocoder_status" : "OK",
         "place_id" : "ChIJ5cGzCGa4yhQRk-lsJUoyizk",
         "types" : [ "street_address" ]
      },
      {
         "geocoder_status" : "OK",
         "place_id" : "ChIJb5VnEF64yhQRCrgps2g77jc",
         "types" : [ "street_address" ]
      }
   ],
"routes" : [
      {
         "bounds" : {
            "northeast" : {
               "lat" : 40.990381,
               "lng" : 29.0282547
            },
            "southwest" : {
               "lat" : 40.9863897,
               "lng" : 29.0216118
            }
         },
         "copyrights" : "Harita verileri ©2019 Google",
         "legs" : [
            {
               "distance" : {
                  "text" : "0,9 km",
                  "value" : 894
               },
               "duration" : {
                  "text" : "11 dakika",
                  "value" : 655
               },
               "end_address" : "Caferağa Mahallesi, Tuğlacı Eminbey Cd. No:5, 34710 Kadıköy/İstanbul, Türkiye",
               "end_location" : {
                  "lat" : 40.9863897,
                  "lng" : 29.0218105
               },
               "start_address" : "Osmanağa Mahallesi, Serasker Cd. No:118, 34714 Kadıköy/İstanbul, Türkiye",
               "start_location" : {
                  "lat" : 40.9893375,
                  "lng" : 29.028225
               },
               "steps" : [
                  {
                     "distance" : {
                        "text" : "8 m",
                        "value" : 8
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 5
                     },
                     "end_location" : {
                        "lat" : 40.9894537,
                        "lng" : 29.0282117
                     },
                     "html_instructions" : "\u003cb\u003eZiya Bey Sk.\u003c/b\u003e adlı yerden \u003cb\u003eSerasker Cd.\u003c/b\u003e hedefine \u003cb\u003ekuzey\u003c/b\u003e yönünde ilerleyin",
                     "polyline" : {
                        "points" : "kvdyFkqdpDGCMA?F"
                     },
                     "start_location" : {
                        "lat" : 40.9893375,
                        "lng" : 29.028225
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "0,3 km",
                        "value" : 326
                     },
                     "duration" : {
                        "text" : "4 dakika",
                        "value" : 215
                     },
                     "end_location" : {
                        "lat" : 40.990381,
                        "lng" : 29.024582
                     },
                     "html_instructions" : "\u003cb\u003eSerasker Cd.\u003c/b\u003e yönünde \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "awdyFiqdpDMxAKr@OjACP[vCEPC^Cf@CLAHENMZ@LQf@Qd@KZENSj@"
                     },
                     "start_location" : {
                        "lat" : 40.9894537,
                        "lng" : 29.0282117
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "34 m",
                        "value" : 34
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 25
                     },
                     "end_location" : {
                        "lat" : 40.9901185,
                        "lng" : 29.0243691
                     },
                     "html_instructions" : "\u003cb\u003eMühürdar Cd.\u003c/b\u003e yönünde \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "{|dyFszcpDHFHF^X"
                     },
                     "start_location" : {
                        "lat" : 40.990381,
                        "lng" : 29.024582
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "8 m",
                        "value" : 8
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 5
                     },
                     "end_location" : {
                        "lat" : 40.990081,
                        "lng" : 29.0242851
                     },
                     "html_instructions" : "\u003cb\u003eMühürdar Cd.\u003c/b\u003e yönünde hafif \u003cb\u003esağa\u003c/b\u003e yönelin",
                     "maneuver" : "turn-slight-right",
                     "polyline" : {
                        "points" : "g{dyFiycpD?D?@?@@??@DB"
                     },
                     "start_location" : {
                        "lat" : 40.9901185,
                        "lng" : 29.0243691
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "7 m",
                        "value" : 7
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 6
                     },
                     "end_location" : {
                        "lat" : 40.9900274,
                        "lng" : 29.0243112
                     },
                     "html_instructions" : "\u003cb\u003eMuvakkıthane Cd.\u003c/b\u003e konumunda \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "_{dyFyxcpDDABA"
                     },
                     "start_location" : {
                        "lat" : 40.990081,
                        "lng" : 29.0242851
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "0,4 km",
                        "value" : 352
                     },
                     "duration" : {
                        "text" : "4 dakika",
                        "value" : 259
                     },
                     "end_location" : {
                        "lat" : 40.987586,
                        "lng" : 29.0217648
                     },
                     "html_instructions" : "\u003cb\u003eMühürdar Cd.\u003c/b\u003e yönünde \u003cb\u003esağa\u003c/b\u003e dönün",
                     "maneuver" : "turn-right",
                     "polyline" : {
                        "points" : "uzdyF}xcpDhAz@pA|@pBtAHRJHRPPNPX\\d@BDHKfAlBDLDHDN@LBN"
                     },
                     "start_location" : {
                        "lat" : 40.9900274,
                        "lng" : 29.0243112
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "63 m",
                        "value" : 63
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 51
                     },
                     "end_location" : {
                        "lat" : 40.987087,
                        "lng" : 29.0216118
                     },
                     "html_instructions" : "\u003cb\u003eMühürdar Cd.\u003c/b\u003e boyunca ilerlemek için \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "mkdyF_icpDNBJ@J@TBJ?JADA@DDN"
                     },
                     "start_location" : {
                        "lat" : 40.987586,
                        "lng" : 29.0217648
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "74 m",
                        "value" : 74
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 64
                     },
                     "end_location" : {
                        "lat" : 40.9864708,
                        "lng" : 29.0216118
                     },
                     "html_instructions" : "\u003cb\u003eMühürdar Cd.\u003c/b\u003e boyunca ilerlemek için \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "ihdyFahcpDJEJAFALAH?VBj@F"
                     },
                     "start_location" : {
                        "lat" : 40.987087,
                        "lng" : 29.0216118
                     },
                     "travel_mode" : "WALKING"
                  },
                  {
                     "distance" : {
                        "text" : "22 m",
                        "value" : 22
                     },
                     "duration" : {
                        "text" : "1 dakika",
                        "value" : 25
                     },
                     "end_location" : {
                        "lat" : 40.9863897,
                        "lng" : 29.0218105
                     },
                     "html_instructions" : "\u003cb\u003eTuğlacı Eminbey Cd.\u003c/b\u003e yönünde \u003cb\u003esola\u003c/b\u003e dönün",
                     "maneuver" : "turn-left",
                     "polyline" : {
                        "points" : "mddyFahcpDNg@"
                     },
                     "start_location" : {
                        "lat" : 40.9864708,
                        "lng" : 29.0216118
                     },
                     "travel_mode" : "WALKING"
                  }
               ],
               "traffic_speed_entry" : [],
               "via_waypoint" : []
            }
         ],
         "overview_polyline" : {
            "points" : "kvdyFkqdpDUEM`B{@hHQfBGXMZ@Lc@lAQj@Sj@HFHF^X?D?B@@DBDABAhAz@bErCHRJHd@`@n@~@BDHKlAzBJXD\\ZD`@DVADA@DDNJERCVAbAJNg@"
         },
         "summary" : "Serasker Cd. ve Mühürdar Cd.",
         "warnings" : [
            "Yürüyerek gitmek için yol tarifi beta özelliğinde mevcuttur. Dikkat – Bu rotada kaldırım veya yaya yolu olmayabilir."
         ],
         "waypoint_order" : []
      }
   ],
   "status" : "OK"
}

我不喜欢反序列化整个对象，因为服务几乎不会使用除了"legs"、"steps"和在"steps"中的"end_location"以外的所有属性。

1
“我不喜欢反序列化整个对象” - 你正在把事情搞得比必要的更困难。JObject.Parse(content)已经在反序列化整个对象了。只需遍历对象图而不是将其转换回字符串并重新解析即可。 - madreflection
1个回答
2
问题在于，您查询 JObject obj 层次结构的选定部分的代码反复将其转换为 JSON 字符串表示形式，而某些时候，您并没有重新解析 JSON 字符串，而是直接将其作为字符串字面量使用。
具体来说，问题出现在以下代码中：
JArray legArray = new JArray();
foreach (JObject item in routeArray)
{
    string leg = item.GetValue("legs").ToString();
    legArray.Add(leg);
}

您正在调用JArray.Add()，但是这个方法有多个重载，所以调用哪一个？由于存在从string到JToken的隐式转换操作符implicit operator，所以leg字符串会被转换为JValue字符串文字，然后添加到JArray中。之后，以下代码将失败并抛出无效转换异常，因为您添加到legArray的项是JValue而不是JObject类型：
foreach (JObject item in legArray)
{

解决方案是简化您的代码，并完全避免在字符串和JToken表示之间来回转换。以下代码可以解决问题：
var endLocationList = obj
    .SelectTokens("routes[*].legs[*].steps[*].end_location")
    .Select(t => t.ToObject<Location>())
    .ToList();

使用类型
public class Location
{
    public double Lat { get; set; }
    public double Lng { get; set; }
}

注释：

  • 您可以使用 JToken.ToObject<T>() 直接从 JToken 反序列化为 POCO。这比将 JToken 格式化为字符串然后反序列化字符串更简单、更高效。

  • JToken.SelectTokens() 允许使用 JSONPath 语法 查询 JSON 层次结构。

    这里的 [*] 表示通配符，选择数组中的所有项目，特别是 "routes"、"legs" 和 "steps" 数组。

    有关更多信息，请参见 # JSONPath - XPath for JSON。

演示代码请点击这里。
这段代码在我的本地机器上运行得非常完美，我的返回模型如下：[{"Legs":[{"Steps":[{"EndLocation":[{"Lat":41.0917854,"Lng":29.0938952},{"Lat":41.0927256,"Lng":29.0943774},{"Lat":41.0931956,"Lng":29.094848},{"Lat":41.094488299999988,"Lng":29.0952805},{"Lat":41.0945246,"Lng":29.0954362},{"Lat":41.0945706,"Lng":29.0955857},{"Lat":41.094365499999988,"Lng":29.0967187}]}]}]}] 但是，当我将此API项目发布到服务器并向返回此模型的方法发送相同的请求时，它返回未填充EndLocation列表的模型。 - RaZzLe
现场项目返回以下内容：[{"Legs":[{"Steps":[{"EndLocation":[]}]}]}] 奇怪的是，我也在另一台服务器上进行了测试，并且它按预期填充了模型。您有任何想法这可能是如何发生的吗？ - RaZzLe
@RaZzLe - 需要看到一个 [mcve]，但也许你没有配置你的服务器使用驼峰命名法？ 可以参考以下链接：如何从ASP.NET MVC控制器方法中序列化camelCase JSON 或者 asp.net core 1.0 web api使用camelcase。 - dbc
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