Deep copy of objects using System.Reflection?

Question

How to do a deep copy of objects using System.Reflection in C# ?

Answer 1

One simple way is to use JSON:

public static T DeepClone<T>(T source)
{
    var serialized = JsonConvert.SerializeObject(source);
    return JsonConvert.DeserializeObject<T>(serialized);
}

which does the reflection for you. Obviously it won't work with anything that, for example, has a handle to an unmanaged object and so on.

(You can use NuGet to install Newtonsoft.Json into your project.)

By default Json won't serialise private fields.

You can fix that like so:

public static T DeepClone<T>(T source)
{
    var settings = new JsonSerializerSettings {ContractResolver = new MyContractResolver()};
    var serialized = JsonConvert.SerializeObject(source, settings);
    return JsonConvert.DeserializeObject<T>(serialized);
}

public class MyContractResolver : DefaultContractResolver
{
    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        var props = type.GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                        .Select(p => base.CreateProperty(p, memberSerialization))
                    .Union(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                                .Select(f => base.CreateProperty(f, memberSerialization)))
                    .ToList();
        props.ForEach(p => { p.Writable = true; p.Readable = true; });
        return props;
    }
}

Here's a full sample console app that shows how an arbitrary class with private fields can be cloned. Note that Json tries to use a constructor to set the fields and/or properties, and if the constructor parameter names don't match the field or property names it won't work correctly:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;

namespace ConsoleApplication1
{
    class Test
    {
        public Test(double y, string s, int x)
        {
            this.Y = y;
            this.s = s;
            this.X = x;
        }

        public int X;

        public double Y { get; private set; }

        public string Z         
        {
            get
            {
                return s;
            }
        }

        private string s;
    }

    class Program
    {
        static void Main()
        {
            var test = new Test(1.2345, "12345", 12345);
            test.X = 12345;

            var copy = DeepClone(test);

            Console.WriteLine("X = " + copy.X);
            Console.WriteLine("Y = " + copy.Y);
            Console.WriteLine("Z = " + copy.Z);
        }

        public static T DeepClone<T>(T source)
        {
            var settings = new JsonSerializerSettings {ContractResolver = new MyContractResolver()};
            var serialized = JsonConvert.SerializeObject(source, settings);
            return JsonConvert.DeserializeObject<T>(serialized);
        }

        public class MyContractResolver : DefaultContractResolver
        {
            protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
            {
                var props = type.GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                                .Select(p => base.CreateProperty(p, memberSerialization))
                            .Union(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
                                        .Select(f => base.CreateProperty(f, memberSerialization)))
                            .ToList();
                props.ForEach(p => { p.Writable = true; p.Readable = true; });
                return props;
            }
        }
    }
}