How to Do a Deep Copy of an Object in .Net

How do you do a deep copy of an object in .NET?

Important Note

BinaryFormatter has been deprecated, and will no longer be available in .NET after November 2023. See BinaryFormatter Obsoletion Strategy

I've seen a few different approaches to this, but I use a generic utility method as such:

public static T DeepClone<T>(this T obj)
{
 using (var ms = new MemoryStream())
 {
   var formatter = new BinaryFormatter();
   formatter.Serialize(ms, obj);
   ms.Position = 0;

   return (T) formatter.Deserialize(ms);
 }
}

Notes:

Your class MUST be marked as [Serializable] for this to work.

Your source file must include the following code:

 using System.Runtime.Serialization.Formatters.Binary;
 using System.IO;

Deep Copy of a C# Object

One of the reasons why your ResultList class won't work with Jon Skeet's example is because it does not implement the ICloneable interface.

Implement ICloneable on all the classes that you need cloned, e.g.

public class ResultItem : ICloneable
{
  public object Clone()
  {
    var item = new ResultItem
                 {
                   ID = ID,
                   Name = Name,
                   isLegit = isLegit
                 };
    return item;
  }
}

And also on ResultList:

public class ResultList<T> : IEnumerable<T>, ICloneable where T : ICloneable
{
  public List<T> Results { get; set; }
  public decimal CenterLatitude { get; set; }
  public decimal CenterLongitude { get; set; }

  public object Clone()
  {
    var list = new ResultList<T>
                 {
                   CenterLatitude = CenterLatitude,
                   CenterLongitude = CenterLongitude,
                   Results = Results.Select(x => x.Clone()).Cast<T>().ToList()
                 };
    return list;
  }
}

Then to make a deep copy of your object:

resultList.clone();

Deep cloning objects

Whereas one approach is to implement the ICloneable interface (described here, so I won't regurgitate), here's a nice deep clone object copier I found on The Code Project a while ago and incorporated it into our code.
As mentioned elsewhere, it requires your objects to be serializable.

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

/// <summary>
/// Reference Article http://www.codeproject.com/KB/tips/SerializedObjectCloner.aspx
/// Provides a method for performing a deep copy of an object.
/// Binary Serialization is used to perform the copy.
/// </summary>
public static class ObjectCopier
{
    /// <summary>
    /// Perform a deep copy of the object via serialization.
    /// </summary>
    /// <typeparam name="T">The type of object being copied.</typeparam>
    /// <param name="source">The object instance to copy.</param>
    /// <returns>A deep copy of the object.</returns>
    public static T Clone<T>(T source)
    {
        if (!typeof(T).IsSerializable)
        {
            throw new ArgumentException("The type must be serializable.", nameof(source));
        }

        // Don't serialize a null object, simply return the default for that object
        if (ReferenceEquals(source, null)) return default;

        using var Stream stream = new MemoryStream();
        IFormatter formatter = new BinaryFormatter();
        formatter.Serialize(stream, source);
        stream.Seek(0, SeekOrigin.Begin);
        return (T)formatter.Deserialize(stream);
    }
}

The idea is that it serializes your object and then deserializes it into a fresh object. The benefit is that you don't have to concern yourself about cloning everything when an object gets too complex.

In case of you prefer to use the new extension methods of C# 3.0, change the method to have the following signature:

public static T Clone<T>(this T source)
{
   // ...
}

Now the method call simply becomes objectBeingCloned.Clone();.

EDIT (January 10 2015) Thought I'd revisit this, to mention I recently started using (Newtonsoft) Json to do this, it should be lighter, and avoids the overhead of [Serializable] tags. (NB @atconway has pointed out in the comments that private members are not cloned using the JSON method)

/// <summary>
/// Perform a deep Copy of the object, using Json as a serialization method. NOTE: Private members are not cloned using this method.
/// </summary>
/// <typeparam name="T">The type of object being copied.</typeparam>
/// <param name="source">The object instance to copy.</param>
/// <returns>The copied object.</returns>
public static T CloneJson<T>(this T source)
{            
    // Don't serialize a null object, simply return the default for that object
    if (ReferenceEquals(source, null)) return default;

    // initialize inner objects individually
    // for example in default constructor some list property initialized with some values,
    // but in 'source' these items are cleaned -
    // without ObjectCreationHandling.Replace default constructor values will be added to result
    var deserializeSettings = new JsonSerializerSettings {ObjectCreationHandling = ObjectCreationHandling.Replace};

    return JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(source), deserializeSettings);
}

Deep cloning objects

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;

/// <summary>
/// Reference Article http://www.codeproject.com/KB/tips/SerializedObjectCloner.aspx
/// Provides a method for performing a deep copy of an object.
/// Binary Serialization is used to perform the copy.
/// </summary>
public static class ObjectCopier
{
    /// <summary>
    /// Perform a deep copy of the object via serialization.
    /// </summary>
    /// <typeparam name="T">The type of object being copied.</typeparam>
    /// <param name="source">The object instance to copy.</param>
    /// <returns>A deep copy of the object.</returns>
    public static T Clone<T>(T source)
    {
        if (!typeof(T).IsSerializable)
        {
            throw new ArgumentException("The type must be serializable.", nameof(source));
        }

        // Don't serialize a null object, simply return the default for that object
        if (ReferenceEquals(source, null)) return default;

        using var Stream stream = new MemoryStream();
        IFormatter formatter = new BinaryFormatter();
        formatter.Serialize(stream, source);
        stream.Seek(0, SeekOrigin.Begin);
        return (T)formatter.Deserialize(stream);
    }
}

In case of you prefer to use the new extension methods of C# 3.0, change the method to have the following signature:

public static T Clone<T>(this T source)
{
   // ...
}

Now the method call simply becomes objectBeingCloned.Clone();.

/// <summary>
/// Perform a deep Copy of the object, using Json as a serialization method. NOTE: Private members are not cloned using this method.
/// </summary>
/// <typeparam name="T">The type of object being copied.</typeparam>
/// <param name="source">The object instance to copy.</param>
/// <returns>The copied object.</returns>
public static T CloneJson<T>(this T source)
{            
    // Don't serialize a null object, simply return the default for that object
    if (ReferenceEquals(source, null)) return default;

    // initialize inner objects individually
    // for example in default constructor some list property initialized with some values,
    // but in 'source' these items are cleaned -
    // without ObjectCreationHandling.Replace default constructor values will be added to result
    var deserializeSettings = new JsonSerializerSettings {ObjectCreationHandling = ObjectCreationHandling.Replace};

    return JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(source), deserializeSettings);
}

deep clone a List of object in c#

Warning: The BinaryFormatter type is dangerous when used with untrusted input. Whilst the usage below should be safe, Microsoft recommend avoiding BinaryFormatter altogether due to its potential for misuse, and will remove it from .NET 7–8. Consider using another serializer or approach for your deep clones.

First off, you can define a utility method for deep-cloning any object (root):

public static T DeepClone<T>(T obj)
{
    using (var stream = new MemoryStream())
    {
        var formatter = new BinaryFormatter();
        formatter.Serialize(stream, obj);
        stream.Position = 0;
        return (T)formatter.Deserialize(stream);
    }
}

If you want to deep-clone myList, all you need to do is pass it as parameter to the method above:

List<SmallClass> myListClone = DeepClone(myList);

The most important consideration you need to pay attention to is that all your classes must be marked as serializable, typically through the [SerializableAttribute].

[SerializableAttribute]
public class SmallClass
{
    // …
}

How to Do a Deep Copy of an Object in .Net

How do you do a deep copy of an object in .NET?

Important Note

Deep Copy of a C# Object

Deep cloning objects

Deep cloning objects

deep clone a List of object in c#

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