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.net c# json

JSON Serializer object with internal properties

I have class with some internal properties and I would like to serialize them into json as well. How can I accomplish this?
For example

public class Foo
{
internal int num1 { get; set; }
internal double num2 { get; set; }
public string Description { get; set; }
public override string ToString()
{
if (!string.IsNullOrEmpty(Description))
return Description;
return base.ToString();
}
}

Saving it using

Foo f = new Foo();
f.Description = "Foo Example";
JsonSerializerSettings settings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All };
string jsonOutput = JsonConvert.SerializeObject(f, Formatting.Indented, settings);
using (StreamWriter sw = new StreamWriter("json_file.json"))
{
sw.WriteLine(jsonOutput);
}

I get

{  
"$type": "SideSlopeTest.Foo, SideSlopeTest",
"Description": "Foo Example"
}

Mark the internal properties to be serialized with the [JsonProperty] attribute:

public class Foo
{
[JsonProperty]
internal int num1 { get; set; }
[JsonProperty]
internal double num2 { get; set; }
public string Description { get; set; }
public override string ToString()
{
if (!string.IsNullOrEmpty(Description))
return Description;
return base.ToString();
}
}

And then later, to test:

Foo f = new Foo();
f.Description = "Foo Example";
f.num1 = 101;
f.num2 = 202;
JsonSerializerSettings settings = new JsonSerializerSettings() { TypeNameHandling = TypeNameHandling.All };
var jsonOutput = JsonConvert.SerializeObject(f, Formatting.Indented, settings);
Console.WriteLine(jsonOutput);

I get the following output:

{
"$type": "Tile.JsonInternalPropertySerialization.Foo, Tile",
"num1": 101,
"num2": 202.0,
"Description": "Foo Example"
}

(Where “Tile.JsonInternalPropertySerialization” and “Tile” are namespace and assembly names I am using).

As an aside, when using TypeNameHandling, do take note of this caution from the Newtonsoft docs:

TypeNameHandling should be used with caution when your application deserializes JSON from an external source. Incoming types should be validated with a custom SerializationBinder when deserializing with a value other than None.

For a discussion of why this may be necessary, see TypeNameHandling caution in Newtonsoft Json and and External json vulnerable because of Json.Net TypeNameHandling auto?.