C#如何处理空json值？Getting and InvalidOperationException:无法访问上的子值>；Newtonsoft.Json.Linq.JValue

我在处理json文件中的空值时遇到问题。如下图所示，空值位于player下：

不幸的是，这导致以下InvalidOperation异常：

System.InvalidOperationException:无法访问上的子值 Newtonsoft.Json.Linq.JValue。 位于Newtonsoft.Json.Linq.JToken.get_项（对象键） 在WindowsFormsApplication2中，在C:\Users\Administrator\documents\visual studio中启动\u Lineups.StartingLineups（） 2015\Projects\WindowsFormsApplication2\WindowsFormsApplication2\Starting 第97行

我尝试了以下方法，但没有成功

JSON:

{"gamestartinglineup":{"lastUpdatedOn":"2017-10-24 11:41:12 AM","game":{"id":"42120","date":"2017-10-24","time":"7:30PM","awayTeam":{"ID":"83","City":"New York","Name":"Knicks","Abbreviation":"NYK"},"homeTeam":{"ID":"82","City":"Boston","Name":"Celtics","Abbreviation":"BOS"},"location":"TD Garden"},"teamLineup":[{"team":{"ID":"83","City":"New York","Name":"Knicks","Abbreviation":"NYK"},"expected":{"starter":[{"position":"Bench8","player":null},{"position":"Starter1","player":{"ID":"9087","LastName":"Hardaway Jr.","FirstName":"Tim","JerseyNumber":"3","Position":"SG"}},{"position":"Starter2","player":{"ID":"9373","LastName":"Porzingis","FirstName":"Kristaps","JerseyNumber":"6","Position":"PF"}},{"position":"Starter5","player":{"ID":"9518","LastName":"Sessions","FirstName":"Ramon","JerseyNumber":"1","Position":"PG"}},{"position":"Starter3","player":{"ID":"9396","LastName":"Kanter","FirstName":"Enes","JerseyNumber":"0","Position":"C"}},{"position":"Starter4","player":{"ID":"9127","LastName":"Lee","FirstName":"Courtney","JerseyNumber":"1","Position":"SG"}},{"position":"Bench1","player":{"ID":"9148","LastName":"McDermott","FirstName":"Doug","JerseyNumber":"20","Position":"SF"}},{"position":"Bench2","player":{"ID":"9376","LastName":"O'Quinn","FirstName":"Kyle","JerseyNumber":"9","Position":"PF"}},{"position":"Bench3","player":{"ID":"9245","LastName":"Beasley","FirstName":"Michael","JerseyNumber":"9","Position":"F"}},{"position":"Bench4","player":{"ID":"10102","LastName":"Baker","FirstName":"Ron","JerseyNumber":"31","Position":"G"}},{"position":"Bench5","player":null},{"position":"Bench6","player":null},{"position":"Bench7","player":null}]},"actual":null},{"team":{"ID":"82","City":"Boston","Name":"Celtics","Abbreviation":"BOS"},"expected":{"starter":[{"position":"Bench8","player":null},{"position":"Starter1","player":{"ID":"13730","LastName":"Tatum","FirstName":"Jayson","JerseyNumber":"0","Position":"F"}},{"position":"Starter2","player":{"ID":"9082","LastName":"Horford","FirstName":"Al","JerseyNumber":"15","Position":"C"}},{"position":"Starter5","player":{"ID":"9157","LastName":"Irving","FirstName":"Kyrie","JerseyNumber":"11","Position":"PG"}},{"position":"Starter3","player":{"ID":"9211","LastName":"Baynes","FirstName":"Aron","JerseyNumber":"12","Position":"C"}},{"position":"Starter4","player":{"ID":"10090","LastName":"Brown","FirstName":"Jaylen","JerseyNumber":"7","Position":"SF"}},{"position":"Bench1","player":{"ID":"13777","LastName":"Theis","FirstName":"Daniel","JerseyNumber":"27","Position":"PF"}},{"position":"Bench2","player":{"ID":"9105","LastName":"Rozier","FirstName":"Terry","JerseyNumber":"12","Position":"PG"}},{"position":"Bench3","player":{"ID":"13770","LastName":"Nader","FirstName":"Abdel","JerseyNumber":"28","Position":"SF"}},{"position":"Bench4","player":{"ID":"9120","LastName":"Larkin","FirstName":"Shane","JerseyNumber":"8","Position":"PG"}},{"position":"Bench5","player":{"ID":"13778","LastName":"Yabusele","FirstName":"Guerschon","JerseyNumber":"30","Position":"PF"}},{"position":"Bench6","player":{"ID":"13771","LastName":"Bird","FirstName":"Jabari","JerseyNumber":"26","Position":"SG"}},{"position":"Bench7","player":null}]},"actual":null}]}}

代码：

    public void StartingLineups()
    {
        upass.upass up = new upass.upass();
        string address3 = "https://api.mysportsfeeds.com/v1.1/pull/nba/2017-2018-regular/game_startinglineup.json?gameid=" + dateTimePicker1.Text + comboBox2.Text;

        var w3 = new WebClient();
        w3.UseDefaultCredentials = true;
        w3.Credentials = new NetworkCredential(up.username, up.password);
        var result3 = w3.DownloadString(address3);

        var obj3 = JObject.Parse(result3);


        StartingLineup.startinglineup sl = new StartingLineup.startinglineup();

        try
       {

            foreach (JToken child in obj3 ["gamestartinglineup"]["teamLineup"])
            {


                    foreach (JToken sub in child["expected"]["starter"])
                    {

                    JsonConvert.SerializeObject(sub,
                        Newtonsoft.Json.Formatting.None,
                        new JsonSerializerSettings
                        {
                            NullValueHandling = NullValueHandling.Ignore
                        });

                    sl.player = sub["player"]["FirstName"].ToString() + " " + sub["player"]["LastName"].ToString();
                        sl.team = child["team"]["City"].ToString() + " " + child["team"]["Name"].ToString();
                        sl.position = sub["position"].ToString();
                        sl.playerpositon = sub["player"]["Position"].ToString();




                        DataRow row = dt.NewRow();
                        row["Team"] = sl.team;
                        row["Player"] = sl.player;
                        row["Position"] = sl.playerpositon;





                        if (sl.position.Contains("Starter"))
                        {
                            row["Role"] = sl.position;
                        }
                        else
                        {
                            row["Role"] = "NOPE";
                        }



                        dt.Rows.Add(row);
                    }
                    dataGridView1.DataSource = dt;

                    DataRow[] drr = dt.Select("Role='NOPE'");
                    for (int i = 0; i < drr.Length; i++)
                        drr[i].Delete();
                    dt.AcceptChanges();




                }



        }
        catch (Exception e)
        {
            MessageBox.Show(e.ToString());

        }

    }

public void StartingLineups（）
{
upass.upass up=新的upass.upass（）；
字符串地址3=”https://api.mysportsfeeds.com/v1.1/pull/nba/2017-2018-regular/game_startinglineup.json?gameid=“+dateTimePicker1.Text+comboBox2.Text；
var w3=新的WebClient（）；
w3.UseDefaultCredentials=true；
w3.Credentials=新的网络凭据（up.username，up.password）；
var result3=w3.DownloadString（地址3）；
var obj3=JObject.Parse（result3）；
StartingLineup.StartingLineup sl=新的StartingLineup.StartingLineup（）；
尝试
{
foreach（obj3[“游戏开始列表”][“团队列表”]中的JToken儿童）
{
foreach（子项中的JToken子项[“预期”][“起始”]）
{
JsonConvert.SerializeObject（子对象，
Newtonsoft.Json.Formatting.None，
新JsonSerializerSettings
{
NullValueHandling=NullValueHandling.Ignore
});
sl.player=sub[“player”][“FirstName”].ToString（）+“”+sub[“player”][“LastName”].ToString（）；
sl.team=child[“team”][“City”].ToString（）+“”+child[“team”][“Name”].ToString（）；
sl.position=sub[“position”].ToString（）；
sl.playerposition=sub[“player”][“Position”].ToString（）；
DataRow row=dt.NewRow（）；
行[“团队”]=sl.Team；
行[“玩家”]=sl.Player；
行[“位置”]=sl.playerposition；
如果（sl.position.包含（“启动器”））
{
行[“角色”]=sl.position；
}
其他的
{
行[“角色”]=“否”；
}
dt.行。添加（行）；
}
dataGridView1.DataSource=dt；
DataRow[]drr=dt.Select（“Role='NOPE'）；
对于（int i=0；i

在检查可空值（）时，请考虑这一点：

var testObj=newnewtonsoft.Json.Linq.JObject（）； if（testObj.TryGetValue（“player”，out Newtonsoft.Json.Linq.JToken令牌））{ string yourString=token.Value（“FirstName”）；//可以为空 int？yourNullableInt=token.Value（“AnyNumber”）；//可以为null int yourInt=token.Value（“AnyNumber”）？？0；//如果为空，则可以为0 int yourInt=token.SelectToken（“第一层”）？.SelectToken（“第二层”）？.Value（“任意数”）？？0；//按路径返回值 }

---

SelectToken也适用于。

在检查可空值（）时，请考虑这一点：

var testObj=newnewtonsoft.Json.Linq.JObject（）； if（testObj.TryGetValue（“player”，out Newtonsoft.Json.Linq.JToken令牌））{ string yourString=token.Value（“FirstName”）；//可以为空 int？yourNullableInt=token.Value（“AnyNumber”）；//可以为null int yourInt=token.Value（“AnyNumber”）？？0；//如果为空，则可以为0 int yourInt=token.SelectToken（“第一层”）？.SelectToken（“第二层”）？.Value（“任意数”）？？0；//按路径返回值 }

---

SelectToken也适用于。

为什么不处理

JsonConvert.SerializeObject（sub，Newtonsoft.Json.Formatting.None，new JsonSerializerSettings）的输出字符串{NullValueHandling=NullValueHandling.Ignore}）

？您仍然必须检查null。这与期望

myNullObject.ChildProperty

成功没有什么不同。

NullValueHandling.Ignore

只意味着如果值为

null

，当您序列化为JSON时属性将不存在。为什么对

JsonConvert.SerializeObjec的输出字符串不做任何操作t（sub，Newtonsoft.Json.Formatting.None，新JsonSerializerSettings{NullValueHandling=NullValueHandling.Ignore}）

？您仍然必须检查null。这与期望

myNullObject.ChildProperty

成功没有什么不同。

NullValueHandling.Ignore

只意味着如果值为

null

，则序列化为JSON时该属性将不存在。

var testObj = new Newtonsoft.Json.Linq.JObject();

if (testObj.TryGetValue("player", out Newtonsoft.Json.Linq.JToken token)) {
 string yourString = token.Value<string>("FirstName"); // can be null
 int? yourNullableInt = token.Value<int?>("AnyNumber"); // can be null
 int yourInt = token.Value<int?>("AnyNumber") ?? 0; // can be 0 if null
 int yourInt = token.SelectToken("firstLayer")?.SelectToken("secondLayer")?.Value<int?>("anyNumber") ?? 0; // return value by path
}