Run default serialization logic from JsonConverter

问题

I have a JsonConverter that, depending on an instance specific flag, needs to either

run custom serialization logic
run the default Json.NET serialization logic

How can the default Json.NET serialization logic be ran from a JsonConverter?

Thanks

回答1:

Here is an example. Say your class to serialize looks like this:

class Foo
{
    public bool IsSpecial { get; set; }
    public string A { get; set; }
    public string B { get; set; }
    public string C { get; set; }
}

The IsSpecial flag is used to control whether we do something special in the converter or just let things serialize naturally. You can write your converter like this:

class FooConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return typeof(Foo).IsAssignableFrom(objectType);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Foo foo = (Foo)value;
        JObject jo;
        if (foo.IsSpecial)
        {
            // special serialization logic based on instance-specific flag
            jo = new JObject();
            jo.Add("names", string.Join(", ", new string[] { foo.A, foo.B, foo.C }));
        }
        else
        {
            // normal serialization
            jo = JObject.FromObject(foo);
        }
        jo.WriteTo(writer);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Then, to use the converter, pass an instance of it to the SerializeObject method (e.g. in the settings). (Do NOT decorate the target class with a JsonConverter attribute, or this will result in an infinite recursive loop when you serialize.)

class Program
{
    static void Main(string[] args)
    {
        List<Foo> foos = new List<Foo>
        {
            new Foo
            {
                A = "Moe",
                B = "Larry",
                C = "Curly",
                IsSpecial = false
            },
            new Foo
            {
                A = "Huey",
                B = "Dewey",
                C = "Louie",
                IsSpecial = true
            },
        };

        JsonSerializerSettings settings = new JsonSerializerSettings();
        settings.Converters.Add(new FooConverter());
        settings.Formatting = Formatting.Indented;

        string json = JsonConvert.SerializeObject(foos, settings);
        Console.WriteLine(json);
    }
}

Output:

[
  {
    "IsSpecial": false,
    "A": "Moe",
    "B": "Larry",
    "C": "Curly"
  },
  {
    "names": "Huey, Dewey, Louie"
  }
]

回答2:

You can change the CanWrite property to disable a custom serializer. This won't work right if the object can contain children of the same type or if you are serializing in more than one thread.

class FooConverter : JsonConverter
{
    bool _canWrite = true;
    public override bool CanWrite
    {
        get { return _canWrite;}
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Foo foo = (Foo)value;
        JObject jo;
        if (foo.IsSpecial)
        {
            // special serialization logic based on instance-specific flag
            jo = new JObject();
            jo.Add("names", string.Join(", ", new string[] { foo.A, foo.B, foo.C }));
        }
        else
        {
            // normal serialization
            _canWrite = false;
            jo = JObject.FromObject(foo);
            _canWrite = true;
        }
        jo.WriteTo(writer);
    }
}

来源：https://stackoverflow.com/questions/21366328/run-default-serialization-logic-from-jsonconverter

标签

serialization

json.net