c# - Json.net how to serialize object as value

Question

I've pored through the docs, StackOverflow, etc., can't seem to find this...

What I want to do is serialize/deserialize a simple value-type of object as a value, not an object, as so:

public class IPAddress
{
    byte[] bytes;

    public override string ToString() {... etc.
}

public class SomeOuterObject
{
    string stringValue;
    IPAddress ipValue;
}

IPAddress ip = new IPAddress("192.168.1.2");
var obj = new SomeOuterObject() {stringValue = "Some String", ipValue = ip};
string json = JsonConverter.SerializeObject(obj);

What I want is for the json to serialize like this:

// json = {"someString":"Some String","ipValue":"192.168.1.2"} <- value serialized as value, not subobject

Not where the ip becomes a nested object, ex:

// json = {"someString":"Some String","ipValue":{"value":"192.168.1.2"}}

Does anyone know how to do this? Thanks! (P.S. I am bolting Json serialization on a large hairy legacy .NET codebase, so I can't really change any existing types, but I can augment/factor/decorate them to facilitate Json serialization.)

Answer 1

You can handle this using a custom JsonConverter for the IPAddress class. Here is the code you would need:

public class IPAddressConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(IPAddress));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return new IPAddress(JToken.Load(reader).ToString());
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        JToken.FromObject(value.ToString()).WriteTo(writer);
    }
}

Then, add a [JsonConverter] attribute to your IPAddress class and you're ready to go:

[JsonConverter(typeof(IPAddressConverter))]
public class IPAddress
{
    byte[] bytes;

    public IPAddress(string address)
    {
        bytes = address.Split('.').Select(s => byte.Parse(s)).ToArray();
    }

    public override string ToString() 
    { 
        return string.Join(".", bytes.Select(b => b.ToString()).ToArray()); 
    }
}

Here is a working demo:

class Program
{
    static void Main(string[] args)
    {
        IPAddress ip = new IPAddress("192.168.1.2");
        var obj = new SomeOuterObject() { stringValue = "Some String", ipValue = ip };
        string json = JsonConvert.SerializeObject(obj);
        Console.WriteLine(json);
    }
}

public class SomeOuterObject
{
    public string stringValue { get; set; }
    public IPAddress ipValue { get; set; }
}

Output:

{"stringValue":"Some String","ipValue":"192.168.1.2"}