Develop Reference

How to use Json deserialization on generic variable in c#

I am trying to use Newtonsoft Json in my project. What I want to do is like below.
public class Subscribe<T> : BaseSubscribe where T : Message, new() // A class
message.body = JsonConvert.DeserializeObject <T.body>(receiveMessage); // In a class member functiton
I got an error. T is a generic variable so I can not initialize. Is there any ways to use json converter on generic variable?
thanks.

try this:
var message = JsonConvert.DeserializeObject<T>(receiveMessage);
var messageBody = message.body;
But please, share more of your code and the error.

If you want to be able to deserialise generic types using JsonConvert then you will need to help the deserialiser by supplying the concrete type name in your json. This is done using the TypeNameHandling flag on the JsonSerializerSettings object. Example below.
[TestFixture]
public class GenericJsonConvertFixture
{
public abstract class Employee
{
public string Name { get; set; }
}
public class Manager : Employee
{
}
public class Subscribe<T> where T : Employee
{
public T Employee { get; set; }
}
[Test]
public async Task TestDeserialisingGenericTypes()
{
var sub = new Subscribe<Employee>()
{
Employee = new Manager() { Name = "Elon" }
};
var json = JsonConvert.SerializeObject(sub, new JsonSerializerSettings()
{
TypeNameHandling = TypeNameHandling.Objects
});
var newSub = JsonConvert.DeserializeObject(json, new JsonSerializerSettings()
{
TypeNameHandling = TypeNameHandling.Objects
});
Assert.That(newSub is Subscribe<Employee>);
Assert.That(((Subscribe<Employee>)newSub).Employee is Manager);
}
}

Upper case JSON keys

Let's say I have a JSON based string that looks: {"Hello":"1"} I want to convert it to look like {"HELLO":"1"}.
I have created an upper case naming strategy:
public class UpperCaseNamingStrategy : NamingStrategy
{
protected override string ResolvePropertyName(string name)
{
return name.ToUpper();
}
}
Which works when manipulating an object:
[Fact]
public void TestUpperCase()
{
var thing = new {Hello = "1"};
var jsonSerializerSettings = new JsonSerializerSettings
{
ContractResolver = new DefaultContractResolver
{
NamingStrategy = new UpperCaseNamingStrategy { OverrideSpecifiedNames = true }
}
};
var serializeObject = JsonConvert.SerializeObject(thing, jsonSerializerSettings);
Assert.Equal("{\"HELLO\":\"1\"}", serializeObject); // Works fine
}
But when I load in a string via the JObject.Parse API, it seems to leave the string as is:
[Fact]
public void TestUpperCase2()
{
var thing = JObject.Parse("{\"Hello\":\"1\"}");
var jsonSerializerSettings = new JsonSerializerSettings
{
ContractResolver = new DefaultContractResolver
{
NamingStrategy = new UpperCaseNamingStrategy { OverrideSpecifiedNames = true }
}
};
var serializeObject = JsonConvert.SerializeObject(thing, jsonSerializerSettings);
Assert.Equal("{\"HELLO\":\"1\"}", serializeObject); // this fails Actual: {"Hello":"1"}
}
In this test I am simulating my use case, I am retrieving a JSON response from a REST API, I am trying to take that response string and convert all of the keys into upper case string.
Doing a little debugging I can see that the object that is getting loaded into the JObject looks something like {{"Hello": "1"}}.
I just want to point out that the data I am using is much more complex than just simple "hello" I just wanted a quick example, let's say I have 20 fields some being objects some being arrays, is there an easy way I can parse the JSON and have all the keys to use upper case naming.

The way I've decided to solve this problem is to create a POCO (plain old c object) to store the information from the API response:
public class Poco
{
public string Hello {get;set;}
}
When I want to upper case all of the property keys send it through the serialization with my Upper case naming strategy:
var responseModel = JsonConvert.DeserializeObject<TResponse>(data);
return JObject.Parse(JsonConvert.SerializeObject(responseModel,
new JsonSerializerSettings
{
DefaultValueHandling = DefaultValueHandling.Ignore,
ContractResolver = new DefaultContractResolver
{
NamingStrategy = new UpperCaseNamingStrategy
{
OverrideSpecifiedNames = true
}
}
}));
I wish there was a more generic way of doing this, but this seems like a sensible solution

So in case someone still tries to figure that out:
Declare a naming policy
public class UpperCaseNamingPolicy : JsonNamingPolicy
{
public override string ConvertName(string name) => name.ToUpper();
}
And in your controller:
using System.Text.Json;
var options = new JsonSerializerOptions
{
PropertyNamingPolicy = new UpperCaseNamingPolicy(),
WriteIndented = true
};
return Json(result, options);

Return json with lower case first letter of property names

I have LoginModel:
public class LoginModel : IData
{
public string Email { get; set; }
public string Password { get; set; }
}
and I have the Web api method
public IHttpActionResult Login([FromBody] LoginModel model)
{
return this.Ok(model);
}
And it's return 200 and body:
{
Email: "dfdf",
Password: "dsfsdf"
}
But I want to get with lower first letter in property like
{
email: "dfdf",
password: "dsfsdf"
}
And I have Json contract resolver for correcting
public class FirstLowerContractResolver : DefaultContractResolver
{
protected override string ResolvePropertyName(string propertyName)
{
if (string.IsNullOrWhiteSpace(propertyName))
return string.Empty;
return $"{char.ToLower(propertyName[0])}{propertyName.Substring(1)}";
}
}
How I can apply this?

If your are using Newtonsoft.Json, you can add JsonProperties to your view model :
public class LoginModel : IData
{
[JsonProperty(PropertyName = "email")]
public string Email {get;set;}
[JsonProperty(PropertyName = "password")]
public string Password {get;set;}
}

To force all json data returned from api to camel case it's easier to use Newtonsoft Json with the default camel case contract resolver.
Create a class like this one:
using Newtonsoft.Json.Serialization;
internal class JsonContentNegotiator : IContentNegotiator
{
private readonly JsonMediaTypeFormatter _jsonFormatter;
public JsonContentNegotiator(JsonMediaTypeFormatter formatter)
{
_jsonFormatter = formatter;
_jsonFormatter.SerializerSettings.ContractResolver =
new CamelCasePropertyNamesContractResolver();
}
public ContentNegotiationResult Negotiate(Type type, HttpRequestMessage request, IEnumerable<MediaTypeFormatter> formatters)
{
return new ContentNegotiationResult(_jsonFormatter, new MediaTypeHeaderValue("application/json"));
}
}
and set this during api configuration (at startup):
var jsonFormatter = new JsonMediaTypeFormatter();
httpConfiguration.Services.Replace(typeof(IContentNegotiator), new JsonContentNegotiator(jsonFormatter));

You can add the two following statement in the configuration of the web API or to the startup file
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.Formatting = Formatting.Indented;
But it is very important to use the return Ok() method instead of return Json() otherwise; this will not work.
if you have to use Json method (and have no other choice)
then see this answer https://stackoverflow.com/a/28960505/4390133

If you need it only in some certain place and not throughout whole application, then you can do following:
var objectToSerialize = new {Property1 = "value1", SubOjbect = new { SubObjectId = 1 }};
var json = Newtonsoft.Json.JsonConvert.SerializeObject(data, new JsonSerializerSettings { ContractResolver = new Newtonsoft.Json.Serialization.CamelCasePropertyNamesContractResolver() });
It should result in {"property1":"value1","subOjbect":{"subObjectId":1}} (note that nested properties also starts from lowercase)

Convert JSON String To C# Object

Trying to convert a JSON string into an object in C#. Using a really simple test case:
JavaScriptSerializer json_serializer = new JavaScriptSerializer();
object routes_list = json_serializer.DeserializeObject("{ \"test\":\"some data\" }");
The problem is that routes_list never gets set; it's an undefined object. Any ideas?

Or, you can use the Newtownsoft.Json library as follows:
using Newtonsoft.Json;
...
var result = JsonConvert.DeserializeObject<T>(json);
Where T is your object type that matches your JSON string.

It looks like you're trying to deserialize to a raw object. You could create a Class that represents the object that you're converting to. This would be most useful in cases where you're dealing with larger objects or JSON Strings.
For instance:
class Test {
String test;
String getTest() { return test; }
void setTest(String test) { this.test = test; }
}
Then your deserialization code would be:
JavaScriptSerializer json_serializer = new JavaScriptSerializer();
Test routes_list =
(Test)json_serializer.DeserializeObject("{ \"test\":\"some data\" }");
More information can be found in this tutorial:
http://www.codeproject.com/Tips/79435/Deserialize-JSON-with-Csharp.aspx

You probably don't want to just declare routes_list as an object type. It doesn't have a .test property, so you really aren't going to get a nice object back. This is one of those places where you would be better off defining a class or a struct, or make use of the dynamic keyword.
If you really want this code to work as you have it, you'll need to know that the object returned by DeserializeObject is a generic dictionary of string,object. Here's the code to do it that way:
var json_serializer = new JavaScriptSerializer();
var routes_list = (IDictionary<string, object>)json_serializer.DeserializeObject("{ \"test\":\"some data\" }");
Console.WriteLine(routes_list["test"]);
If you want to use the dynamic keyword, you can read how here.
If you declare a class or struct, you can call Deserialize instead of DeserializeObject like so:
class MyProgram {
struct MyObj {
public string test { get; set; }
}
static void Main(string[] args) {
var json_serializer = new JavaScriptSerializer();
MyObj routes_list = json_serializer.Deserialize<MyObj>("{ \"test\":\"some data\" }");
Console.WriteLine(routes_list.test);
Console.WriteLine("Done...");
Console.ReadKey(true);
}
}

Using dynamic object with JavaScriptSerializer.
JavaScriptSerializer serializer = new JavaScriptSerializer();
dynamic item = serializer.Deserialize<object>("{ \"test\":\"some data\" }");
string test= item["test"];
//test Result = "some data"

Newtonsoft is faster than java script serializer. ... this one depends on the Newtonsoft NuGet package, which is popular and better than the default serializer.
one line code solution.
var myclass = Newtonsoft.Json.JsonConvert.DeserializeObject<dynamic>(Jsonstring);
Myclass oMyclass = Newtonsoft.Json.JsonConvert.DeserializeObject<Myclass>(Jsonstring);

You can accomplished your requirement easily by using Newtonsoft.Json library. I am writing down the one example below have a look into it.
Class for the type of object you receive:
public class User
{
public int ID { get; set; }
public string Name { get; set; }
}
Code:
static void Main(string[] args)
{
string json = "{\"ID\": 1, \"Name\": \"Abdullah\"}";
User user = JsonConvert.DeserializeObject<User>(json);
Console.ReadKey();
}
this is a very simple way to parse your json.

Here's a simple class I cobbled together from various posts.... It's been tested for about 15 minutes, but seems to work for my purposes. It uses JavascriptSerializer to do the work, which can be referenced in your app using the info detailed in this post.
The below code can be run in LinqPad to test it out by:
Right clicking on your script tab in LinqPad, and choosing "Query
Properties"
Referencing the "System.Web.Extensions.dll" in "Additional References"
Adding an "Additional Namespace Imports" of
"System.Web.Script.Serialization".
Hope it helps!
void Main()
{
string json = #"
{
'glossary':
{
'title': 'example glossary',
'GlossDiv':
{
'title': 'S',
'GlossList':
{
'GlossEntry':
{
'ID': 'SGML',
'ItemNumber': 2,
'SortAs': 'SGML',
'GlossTerm': 'Standard Generalized Markup Language',
'Acronym': 'SGML',
'Abbrev': 'ISO 8879:1986',
'GlossDef':
{
'para': 'A meta-markup language, used to create markup languages such as DocBook.',
'GlossSeeAlso': ['GML', 'XML']
},
'GlossSee': 'markup'
}
}
}
}
}
";
var d = new JsonDeserializer(json);
d.GetString("glossary.title").Dump();
d.GetString("glossary.GlossDiv.title").Dump();
d.GetString("glossary.GlossDiv.GlossList.GlossEntry.ID").Dump();
d.GetInt("glossary.GlossDiv.GlossList.GlossEntry.ItemNumber").Dump();
d.GetObject("glossary.GlossDiv.GlossList.GlossEntry.GlossDef").Dump();
d.GetObject("glossary.GlossDiv.GlossList.GlossEntry.GlossDef.GlossSeeAlso").Dump();
d.GetObject("Some Path That Doesnt Exist.Or.Another").Dump();
}
// Define other methods and classes here
public class JsonDeserializer
{
private IDictionary<string, object> jsonData { get; set; }
public JsonDeserializer(string json)
{
var json_serializer = new JavaScriptSerializer();
jsonData = (IDictionary<string, object>)json_serializer.DeserializeObject(json);
}
public string GetString(string path)
{
return (string) GetObject(path);
}
public int? GetInt(string path)
{
int? result = null;
object o = GetObject(path);
if (o == null)
{
return result;
}
if (o is string)
{
result = Int32.Parse((string)o);
}
else
{
result = (Int32) o;
}
return result;
}
public object GetObject(string path)
{
object result = null;
var curr = jsonData;
var paths = path.Split('.');
var pathCount = paths.Count();
try
{
for (int i = 0; i < pathCount; i++)
{
var key = paths[i];
if (i == (pathCount - 1))
{
result = curr[key];
}
else
{
curr = (IDictionary<string, object>)curr[key];
}
}
}
catch
{
// Probably means an invalid path (ie object doesn't exist)
}
return result;
}
}

As tripletdad99 said
var result = JsonConvert.DeserializeObject<T>(json);
but if you don't want to create an extra object you can make it with Dictionary instead
var result = JsonConvert.DeserializeObject<Dictionary<string, string>>(json_serializer);

add this ddl to reference to your project: System.Web.Extensions.dll
use this namespace: using System.Web.Script.Serialization;
public class IdName
{
public int Id { get; set; }
public string Name { get; set; }
}
string jsonStringSingle = "{'Id': 1, 'Name':'Thulasi Ram.S'}".Replace("'", "\"");
var entity = new JavaScriptSerializer().Deserialize<IdName>(jsonStringSingle);
string jsonStringCollection = "[{'Id': 2, 'Name':'Thulasi Ram.S'},{'Id': 2, 'Name':'Raja Ram.S'},{'Id': 3, 'Name':'Ram.S'}]".Replace("'", "\"");
var collection = new JavaScriptSerializer().Deserialize<IEnumerable<IdName>>(jsonStringCollection);

Copy your Json and paste at textbox on json2csharp and click on Generate button.
A cs class will be generated use that cs file as below
var generatedcsResponce = JsonConvert.DeserializeObject(yourJson);
Where RootObject is the name of the generated cs file;

Another fast and easy way to semi-automate these steps is to:
take the JSON you want to parse and paste it here: https://app.quicktype.io/ . Change language to C# in the drop down.
Update the name in the top left to your class name, it defaults to "Welcome".
In visual studio go to Website -> Manage Packages and use NuGet to add Json.Net from Newtonsoft.
app.quicktype.io generated serialize methods based on Newtonsoft.
Alternatively, you can now use code like:
WebClient client = new WebClient();
string myJSON = client.DownloadString("https://URL_FOR_JSON.com/JSON_STUFF");
var myClass = Newtonsoft.Json.JsonConvert.DeserializeObject(myJSON);

Convert a JSON string into an object in C#. Using below test case.. its worked for me. Here "MenuInfo" is my C# class object.
JsonTextReader reader = null;
try
{
WebClient webClient = new WebClient();
JObject result = JObject.Parse(webClient.DownloadString("YOUR URL"));
reader = new JsonTextReader(new System.IO.StringReader(result.ToString()));
reader.SupportMultipleContent = true;
}
catch(Exception)
{}
JsonSerializer serializer = new JsonSerializer();
MenuInfo menuInfo = serializer.Deserialize<MenuInfo>(reader);

First you have to include library like:
using System.Runtime.Serialization.Json;
DataContractJsonSerializer desc = new DataContractJsonSerializer(typeof(BlogSite));
string json = "{\"Description\":\"Share knowledge\",\"Name\":\"zahid\"}";
using (var ms = new MemoryStream(ASCIIEncoding.ASCII.GetBytes(json)))
{
BlogSite b = (BlogSite)desc.ReadObject(ms);
Console.WriteLine(b.Name);
Console.WriteLine(b.Description);
}

Let's assume you have a class name Student it has following fields and it has a method which will take JSON as a input and return a string Student Object.We can use JavaScriptSerializer here Convert JSON String To C# Object.std is a JSON string here.
public class Student
{
public string FirstName {get;set:}
public string LastName {get;set:}
public int[] Grades {get;set:}
}
public static Student ConvertToStudent(string std)
{
var serializer = new JavaScriptSerializer();
Return serializer.Deserialize<Student>(std);
}

Or, you can use the System.Text.Json library as follows:
using System.Text.Json;
...
var options = new JsonSerializerOptions()
{
PropertyNameCaseInsensitive = true
});
var result = JsonSerializer.Deserialize<List<T>>(json, options);
Where T is your object type that matches your JSON string.
System.Text.Json is available in:
.NET Core 2.0 and above
.NET Framework 4.6.1 and above

How to create JSON string in C#

I just used the XmlWriter to create some XML to send back in an HTTP response. How would you create a JSON string. I assume you would just use a stringbuilder to build the JSON string and them format your response as JSON?

Using Newtonsoft.Json makes it really easier:
Product product = new Product();
product.Name = "Apple";
product.Expiry = new DateTime(2008, 12, 28);
product.Price = 3.99M;
product.Sizes = new string[] { "Small", "Medium", "Large" };
string json = JsonConvert.SerializeObject(product);
Documentation: Serializing and Deserializing JSON

You could use the JavaScriptSerializer class, check this article to build an useful extension method.
Code from article:
namespace ExtensionMethods
{
public static class JSONHelper
{
public static string ToJSON(this object obj)
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
return serializer.Serialize(obj);
}
public static string ToJSON(this object obj, int recursionDepth)
{
JavaScriptSerializer serializer = new JavaScriptSerializer();
serializer.RecursionLimit = recursionDepth;
return serializer.Serialize(obj);
}
}
}
Usage:
using ExtensionMethods;
...
List<Person> people = new List<Person>{
new Person{ID = 1, FirstName = "Scott", LastName = "Gurthie"},
new Person{ID = 2, FirstName = "Bill", LastName = "Gates"}
};
string jsonString = people.ToJSON();

Simlpe use of Newtonsoft.Json and Newtonsoft.Json.Linq libraries.
//Create my object
var myData = new
{
Host = #"sftp.myhost.gr",
UserName = "my_username",
Password = "my_password",
SourceDir = "/export/zip/mypath/",
FileName = "my_file.zip"
};
//Tranform it to Json object
string jsonData = JsonConvert.SerializeObject(myData);
//Print the Json object
Console.WriteLine(jsonData);
//Parse the json object
JObject jsonObject = JObject.Parse(jsonData);
//Print the parsed Json object
Console.WriteLine((string)jsonObject["Host"]);
Console.WriteLine((string)jsonObject["UserName"]);
Console.WriteLine((string)jsonObject["Password"]);
Console.WriteLine((string)jsonObject["SourceDir"]);
Console.WriteLine((string)jsonObject["FileName"]);

This library is very good for JSON from C#
http://james.newtonking.com/pages/json-net.aspx

This code snippet uses the DataContractJsonSerializer from System.Runtime.Serialization.Json in .NET 3.5.
public static string ToJson<T>(/* this */ T value, Encoding encoding)
{
var serializer = new DataContractJsonSerializer(typeof(T));
using (var stream = new MemoryStream())
{
using (var writer = JsonReaderWriterFactory.CreateJsonWriter(stream, encoding))
{
serializer.WriteObject(writer, value);
}
return encoding.GetString(stream.ToArray());
}
}

If you need complex result (embedded) create your own structure:
class templateRequest
{
public String[] registration_ids;
public Data data;
public class Data
{
public String message;
public String tickerText;
public String contentTitle;
public Data(String message, String tickerText, string contentTitle)
{
this.message = message;
this.tickerText = tickerText;
this.contentTitle = contentTitle;
}
};
}
and then you can obtain JSON string with calling
List<String> ids = new List<string>() { "id1", "id2" };
templateRequest request = new templeteRequest();
request.registration_ids = ids.ToArray();
request.data = new templateRequest.Data("Your message", "Your ticker", "Your content");
string json = new JavaScriptSerializer().Serialize(request);
The result will be like this:
json = "{\"registration_ids\":[\"id1\",\"id2\"],\"data\":{\"message\":\"Your message\",\"tickerText\":\"Your ticket\",\"contentTitle\":\"Your content\"}}"
Hope it helps!

You can also try my ServiceStack JsonSerializer it's the fastest .NET JSON serializer at the moment. It supports serializing DataContracts, any POCO Type, Interfaces, Late-bound objects including anonymous types, etc.
Basic Example
var customer = new Customer { Name="Joe Bloggs", Age=31 };
var json = JsonSerializer.SerializeToString(customer);
var fromJson = JsonSerializer.DeserializeFromString<Customer>(json);
Note: Only use Microsofts JavaScriptSerializer if performance is not important to you as I've had to leave it out of my benchmarks since its up to 40x-100x slower than the other JSON serializers.

Take a look at http://www.codeplex.com/json/ for the json-net.aspx project. Why re-invent the wheel?

If you want to avoid creating a class and create JSON then Create a dynamic Object and Serialize Object.
dynamic data = new ExpandoObject();
data.name = "kushal";
data.isActive = true;
// convert to JSON
string json = Newtonsoft.Json.JsonConvert.SerializeObject(data);
Read the JSON and deserialize like this:
// convert back to Object
dynamic output = Newtonsoft.Json.JsonConvert.DeserializeObject(json);
// read a particular value:
output.name.Value
ExpandoObject is from System.Dynamic namespace.

If you can't or don't want to use the two built-in JSON serializers (JavaScriptSerializer and DataContractJsonSerializer) you can try the JsonExSerializer library - I use it in a number of projects and works quite well.

If you're trying to create a web service to serve data over JSON to a web page, consider using the ASP.NET Ajax toolkit:
http://www.asp.net/learn/ajax/tutorial-05-cs.aspx
It will automatically convert your objects served over a webservice to json, and create the proxy class that you can use to connect to it.

Encode Usage
Simple object to JSON Array EncodeJsObjectArray()
public class dummyObject
{
public string fake { get; set; }
public int id { get; set; }
public dummyObject()
{
fake = "dummy";
id = 5;
}
public override string ToString()
{
StringBuilder sb = new StringBuilder();
sb.Append('[');
sb.Append(id);
sb.Append(',');
sb.Append(JSONEncoders.EncodeJsString(fake));
sb.Append(']');
return sb.ToString();
}
}
dummyObject[] dummys = new dummyObject[2];
dummys[0] = new dummyObject();
dummys[1] = new dummyObject();
dummys[0].fake = "mike";
dummys[0].id = 29;
string result = JSONEncoders.EncodeJsObjectArray(dummys);
Result:
[[29,"mike"],[5,"dummy"]]
Pretty Usage
Pretty print JSON Array PrettyPrintJson() string extension method
string input = "[14,4,[14,\"data\"],[[5,\"10.186.122.15\"],[6,\"10.186.122.16\"]]]";
string result = input.PrettyPrintJson();
Results is:
[
14,
4,
[
14,
"data"
],
[
[
5,
"10.186.122.15"
],
[
6,
"10.186.122.16"
]
]
]

The DataContractJSONSerializer will do everything for you with the same easy as the XMLSerializer. Its trivial to use this in a web app. If you are using WCF, you can specify its use with an attribute. The DataContractSerializer family is also very fast.

I've found that you don't need the serializer at all. If you return the object as a List.
Let me use an example.
In our asmx we get the data using the variable we passed along
// return data
[WebMethod(CacheDuration = 180)]
public List<latlon> GetData(int id)
{
var data = from p in db.property
where p.id == id
select new latlon
{
lat = p.lat,
lon = p.lon
};
return data.ToList();
}
public class latlon
{
public string lat { get; set; }
public string lon { get; set; }
}
Then using jquery we access the service, passing along that variable.
// get latlon
function getlatlon(propertyid) {
var mydata;
$.ajax({
url: "getData.asmx/GetLatLon",
type: "POST",
data: "{'id': '" + propertyid + "'}",
async: false,
contentType: "application/json;",
dataType: "json",
success: function (data, textStatus, jqXHR) { //
mydata = data;
},
error: function (xmlHttpRequest, textStatus, errorThrown) {
console.log(xmlHttpRequest.responseText);
console.log(textStatus);
console.log(errorThrown);
}
});
return mydata;
}
// call the function with your data
latlondata = getlatlon(id);
And we get our response.
{"d":[{"__type":"MapData+latlon","lat":"40.7031420","lon":"-80.6047970}]}

Include:
using System.Text.Json;
Then serialize your object_to_serialize like this:
JsonSerializer.Serialize(object_to_serialize)