Newtonsoft JsonConvert.DefaultSettings奇怪的行为

Question

I've faced with strange behavior(at least for me) of JsonConvert.DefaultSettings
In my apps i define default json settings for whole app, but in case if i need exclusive serialization of some object i thought that i can pass JsonSerializerSettings as second argument to JsonConvert.SerializeObject and that settings will override the default one. but it seems that this is not correct.

I found that settings passed as second argument are ignored. so, if i need exclusive serialization and there is defined default settings i have to do something like that:

var defs = JsonConvert.DefaultSettings;
JsonConvert.DefaultSettings = null;
var settings = new JsonSerializerSettings();
var jsonString = JsonConvert.SerializeObject(someObject, settings);
JsonConvert.DefaultSettings = defs;

Question : Is it a bug or i just do not understand something? if its not a bug, can someone explain me this behavior?

Suddenly i can not prepare fiddle at the moment because of broken nuget packages at https://dotnetfiddle.net

but here is an example of this case:

using System;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;
using Newtonsoft.Json.Serialization;

public class Program
{
    public enum TestEnum {
        Zero,
        One,
        Two
    }

    public class Something
    {
        public string Name {get; set;}
        public TestEnum Num {get; set;}
    }

    public void Main()
    {
        var test = new Something {
            Name = "foo",
            Num = TestEnum.One
        };

        string json = JsonConvert.SerializeObject(test);
        Console.WriteLine(json);
        // {"Name":"foo","Num":1}

        JsonConvert.DefaultSettings = (() =>
            {
            var JsonSetting = new JsonSerializerSettings
            {
                ContractResolver = new CamelCasePropertyNamesContractResolver(),
            };
            JsonSetting.Converters.Add(new StringEnumConverter()
            {
                CamelCaseText = true
            });

            return JsonSetting;
        });     


        json = JsonConvert.SerializeObject(test);
        Console.WriteLine(json);
        //{"name":"foo","num":"one"}


        var settings = new JsonSerializerSettings();
        json = JsonConvert.SerializeObject(test, settings);
        Console.WriteLine(json);
        //this will result in: {"name":"foo","num":"one"}
        //but i expect this:  {"Name":"foo","Num":1}

    }
}

Answer 1

If you instantiate a new JsonSerializerSettings instance, its ContractResolver property is null . Then in JsonConvert.SerializeObject() , a JsonSerializer is instantiated and configured with the passed settings.

Relevant code:

if (settings.ContractResolver != null)
    serializer.ContractResolver = settings.ContractResolver;

The JsonSerializer 's constructor initializes its ContractResolver to DefaultContractResolver.Instance . So if you don't specify a contract resolver in the settings you pass, it'll resolve to the default.