如何在 .NET 中对对象进行深层复制？ [复制]

Question

我想要一个真正的深拷贝。在 Java 中，这很容易，但在 C# 中如何做到这一点？

Answer 1

重要提示

BinaryFormatter 已被弃用，2023 年 11 月后将不再在 .NET 中可用。请参阅 BinaryFormatter Obsoletion Strategy

---

我已经看到了几种不同的方法，但我使用了一个通用的实用方法：

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);
 }
}

注意事项：

• 您的班级必须标记为 [Serializable] 才能正常工作。

• 您的源文件必须包含以下代码：

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

Answer 2

我wrote a deep object copy extension method，基于递归“MemberwiseClone”。它速度很快（比 BinaryFormatter 快三倍），并且适用于任何对象。您不需要默认构造函数或可序列化的属性。

源代码：

using System.Collections.Generic;
using System.Reflection;
using System.ArrayExtensions;

namespace System
{
    public static class ObjectExtensions
    {
        private static readonly MethodInfo CloneMethod = typeof(Object).GetMethod("MemberwiseClone", BindingFlags.NonPublic | BindingFlags.Instance);

        public static bool IsPrimitive(this Type type)
        {
            if (type == typeof(String)) return true;
            return (type.IsValueType & type.IsPrimitive);
        }

        public static Object Copy(this Object originalObject)
        {
            return InternalCopy(originalObject, new Dictionary<Object, Object>(new ReferenceEqualityComparer()));
        }
        private static Object InternalCopy(Object originalObject, IDictionary<Object, Object> visited)
        {
            if (originalObject == null) return null;
            var typeToReflect = originalObject.GetType();
            if (IsPrimitive(typeToReflect)) return originalObject;
            if (visited.ContainsKey(originalObject)) return visited[originalObject];
            if (typeof(Delegate).IsAssignableFrom(typeToReflect)) return null;
            var cloneObject = CloneMethod.Invoke(originalObject, null);
            if (typeToReflect.IsArray)
            {
                var arrayType = typeToReflect.GetElementType();
                if (IsPrimitive(arrayType) == false)
                {
                    Array clonedArray = (Array)cloneObject;
                    clonedArray.ForEach((array, indices) => array.SetValue(InternalCopy(clonedArray.GetValue(indices), visited), indices));
                }

            }
            visited.Add(originalObject, cloneObject);
            CopyFields(originalObject, visited, cloneObject, typeToReflect);
            RecursiveCopyBaseTypePrivateFields(originalObject, visited, cloneObject, typeToReflect);
            return cloneObject;
        }

        private static void RecursiveCopyBaseTypePrivateFields(object originalObject, IDictionary<object, object> visited, object cloneObject, Type typeToReflect)
        {
            if (typeToReflect.BaseType != null)
            {
                RecursiveCopyBaseTypePrivateFields(originalObject, visited, cloneObject, typeToReflect.BaseType);
                CopyFields(originalObject, visited, cloneObject, typeToReflect.BaseType, BindingFlags.Instance | BindingFlags.NonPublic, info => info.IsPrivate);
            }
        }

        private static void CopyFields(object originalObject, IDictionary<object, object> visited, object cloneObject, Type typeToReflect, BindingFlags bindingFlags = BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.FlattenHierarchy, Func<FieldInfo, bool> filter = null)
        {
            foreach (FieldInfo fieldInfo in typeToReflect.GetFields(bindingFlags))
            {
                if (filter != null && filter(fieldInfo) == false) continue;
                if (IsPrimitive(fieldInfo.FieldType)) continue;
                var originalFieldValue = fieldInfo.GetValue(originalObject);
                var clonedFieldValue = InternalCopy(originalFieldValue, visited);
                fieldInfo.SetValue(cloneObject, clonedFieldValue);
            }
        }
        public static T Copy<T>(this T original)
        {
            return (T)Copy((Object)original);
        }
    }

    public class ReferenceEqualityComparer : EqualityComparer<Object>
    {
        public override bool Equals(object x, object y)
        {
            return ReferenceEquals(x, y);
        }
        public override int GetHashCode(object obj)
        {
            if (obj == null) return 0;
            return obj.GetHashCode();
        }
    }

    namespace ArrayExtensions
    {
        public static class ArrayExtensions
        {
            public static void ForEach(this Array array, Action<Array, int[]> action)
            {
                if (array.LongLength == 0) return;
                ArrayTraverse walker = new ArrayTraverse(array);
                do action(array, walker.Position);
                while (walker.Step());
            }
        }

        internal class ArrayTraverse
        {
            public int[] Position;
            private int[] maxLengths;

            public ArrayTraverse(Array array)
            {
                maxLengths = new int[array.Rank];
                for (int i = 0; i < array.Rank; ++i)
                {
                    maxLengths[i] = array.GetLength(i) - 1;
                }
                Position = new int[array.Rank];
            }

            public bool Step()
            {
                for (int i = 0; i < Position.Length; ++i)
                {
                    if (Position[i] < maxLengths[i])
                    {
                        Position[i]++;
                        for (int j = 0; j < i; j++)
                        {
                            Position[j] = 0;
                        }
                        return true;
                    }
                }
                return false;
            }
        }
    }

}

Answer 3

基于 Kilhoffer 的解决方案...

使用 C# 3.0，您可以按如下方式创建扩展方法：

public static class ExtensionMethods
{
    // Deep clone
    public static T DeepClone<T>(this T a)
    {
        using (MemoryStream stream = new MemoryStream())
        {
            BinaryFormatter formatter = new BinaryFormatter();
            formatter.Serialize(stream, a);
            stream.Position = 0;
            return (T) formatter.Deserialize(stream);
        }
    }
}

使用 DeepClone 方法扩展任何标记为 [Serializable] 的类

MyClass copy = obj.DeepClone();

Answer 4

您可以使用 Nested MemberwiseClone 进行深层复制。它与复制值结构的速度几乎相同，并且比 (a) 反射或 (b) 序列化快一个数量级（如本页其他答案中所述）。

请注意，如果您使用 Nested MemberwiseClone 进行深层复制，您必须为类中的每个嵌套级别手动实现 ShallowCopy，以及调用所有的 DeepCopy表示创建完整克隆的 ShallowCopy 方法。这很简单：总共只有几行，见下面的演示代码。

这是显示相对性能差异的代码输出（深度嵌套的 MemberwiseCopy 为 4.77 秒，序列化为 39.93 秒）。使用嵌套的 MemberwiseCopy 几乎与复制结构一样快，并且复制结构非常接近 .NET 能够达到的理论最大速度，这可能非常接近 C 或 C++ 中相同事物的速度（但会必须运行一些等效的基准来检查此声明）。

    Demo of shallow and deep copy, using classes and MemberwiseClone:
      Create Bob
        Bob.Age=30, Bob.Purchase.Description=Lamborghini
      Clone Bob >> BobsSon
      Adjust BobsSon details
        BobsSon.Age=2, BobsSon.Purchase.Description=Toy car
      Proof of deep copy: If BobsSon is a true clone, then adjusting BobsSon details will not affect Bob:
        Bob.Age=30, Bob.Purchase.Description=Lamborghini
      Elapsed time: 00:00:04.7795670,30000000
    Demo of shallow and deep copy, using structs and value copying:
      Create Bob
        Bob.Age=30, Bob.Purchase.Description=Lamborghini
      Clone Bob >> BobsSon
      Adjust BobsSon details:
        BobsSon.Age=2, BobsSon.Purchase.Description=Toy car
      Proof of deep copy: If BobsSon is a true clone, then adjusting BobsSon details will not affect Bob:
        Bob.Age=30, Bob.Purchase.Description=Lamborghini
      Elapsed time: 00:00:01.0875454,30000000
    Demo of deep copy, using class and serialize/deserialize:
      Elapsed time: 00:00:39.9339425,30000000

要了解如何使用 MemberwiseCopy 进行深度复制，以下是演示项目：

// Nested MemberwiseClone example. 
// Added to demo how to deep copy a reference class.
[Serializable] // Not required if using MemberwiseClone, only used for speed comparison using serialization.
public class Person
{
    public Person(int age, string description)
    {
        this.Age = age;
        this.Purchase.Description = description;
    }
    [Serializable] // Not required if using MemberwiseClone
    public class PurchaseType
    {
        public string Description;
        public PurchaseType ShallowCopy()
        {
            return (PurchaseType)this.MemberwiseClone();
        }
    }
    public PurchaseType Purchase = new PurchaseType();
    public int Age;
    // Add this if using nested MemberwiseClone.
    // This is a class, which is a reference type, so cloning is more difficult.
    public Person ShallowCopy()
    {
        return (Person)this.MemberwiseClone();
    }
    // Add this if using nested MemberwiseClone.
    // This is a class, which is a reference type, so cloning is more difficult.
    public Person DeepCopy()
    {
            // Clone the root ...
        Person other = (Person) this.MemberwiseClone();
            // ... then clone the nested class.
        other.Purchase = this.Purchase.ShallowCopy();
        return other;
    }
}
// Added to demo how to copy a value struct (this is easy - a deep copy happens by default)
public struct PersonStruct
{
    public PersonStruct(int age, string description)
    {
        this.Age = age;
        this.Purchase.Description = description;
    }
    public struct PurchaseType
    {
        public string Description;
    }
    public PurchaseType Purchase;
    public int Age;
    // This is a struct, which is a value type, so everything is a clone by default.
    public PersonStruct ShallowCopy()
    {
        return (PersonStruct)this;
    }
    // This is a struct, which is a value type, so everything is a clone by default.
    public PersonStruct DeepCopy()
    {
        return (PersonStruct)this;
    }
}
// Added only for a speed comparison.
public class MyDeepCopy
{
    public static T DeepCopy<T>(T obj)
    {
        object result = null;
        using (var ms = new MemoryStream())
        {
            var formatter = new BinaryFormatter();
            formatter.Serialize(ms, obj);
            ms.Position = 0;
            result = (T)formatter.Deserialize(ms);
            ms.Close();
        }
        return (T)result;
    }
}

然后，从 main 调用演示：

    void MyMain(string[] args)
    {
        {
            Console.Write("Demo of shallow and deep copy, using classes and MemberwiseCopy:\n");
            var Bob = new Person(30, "Lamborghini");
            Console.Write("  Create Bob\n");
            Console.Write("    Bob.Age={0}, Bob.Purchase.Description={1}\n", Bob.Age, Bob.Purchase.Description);
            Console.Write("  Clone Bob >> BobsSon\n");
            var BobsSon = Bob.DeepCopy();
            Console.Write("  Adjust BobsSon details\n");
            BobsSon.Age = 2;
            BobsSon.Purchase.Description = "Toy car";
            Console.Write("    BobsSon.Age={0}, BobsSon.Purchase.Description={1}\n", BobsSon.Age, BobsSon.Purchase.Description);
            Console.Write("  Proof of deep copy: If BobsSon is a true clone, then adjusting BobsSon details will not affect Bob:\n");
            Console.Write("    Bob.Age={0}, Bob.Purchase.Description={1}\n", Bob.Age, Bob.Purchase.Description);
            Debug.Assert(Bob.Age == 30);
            Debug.Assert(Bob.Purchase.Description == "Lamborghini");
            var sw = new Stopwatch();
            sw.Start();
            int total = 0;
            for (int i = 0; i < 100000; i++)
            {
                var n = Bob.DeepCopy();
                total += n.Age;
            }
            Console.Write("  Elapsed time: {0},{1}\n", sw.Elapsed, total);
        }
        {               
            Console.Write("Demo of shallow and deep copy, using structs:\n");
            var Bob = new PersonStruct(30, "Lamborghini");
            Console.Write("  Create Bob\n");
            Console.Write("    Bob.Age={0}, Bob.Purchase.Description={1}\n", Bob.Age, Bob.Purchase.Description);
            Console.Write("  Clone Bob >> BobsSon\n");
            var BobsSon = Bob.DeepCopy();
            Console.Write("  Adjust BobsSon details:\n");
            BobsSon.Age = 2;
            BobsSon.Purchase.Description = "Toy car";
            Console.Write("    BobsSon.Age={0}, BobsSon.Purchase.Description={1}\n", BobsSon.Age, BobsSon.Purchase.Description);
            Console.Write("  Proof of deep copy: If BobsSon is a true clone, then adjusting BobsSon details will not affect Bob:\n");
            Console.Write("    Bob.Age={0}, Bob.Purchase.Description={1}\n", Bob.Age, Bob.Purchase.Description);                
            Debug.Assert(Bob.Age == 30);
            Debug.Assert(Bob.Purchase.Description == "Lamborghini");
            var sw = new Stopwatch();
            sw.Start();
            int total = 0;
            for (int i = 0; i < 100000; i++)
            {
                var n = Bob.DeepCopy();
                total += n.Age;
            }
            Console.Write("  Elapsed time: {0},{1}\n", sw.Elapsed, total);
        }
        {
            Console.Write("Demo of deep copy, using class and serialize/deserialize:\n");
            int total = 0;
            var sw = new Stopwatch();
            sw.Start();
            var Bob = new Person(30, "Lamborghini");
            for (int i = 0; i < 100000; i++)
            {
                var BobsSon = MyDeepCopy.DeepCopy<Person>(Bob);
                total += BobsSon.Age;
            }
            Console.Write("  Elapsed time: {0},{1}\n", sw.Elapsed, total);
        }
        Console.ReadKey();
    }

再次注意，如果您使用 Nested MemberwiseClone 进行深层复制，您必须为类中的每个嵌套级别手动实现一个 ShallowCopy，以及一个 DeepCopy调用所有所说的 ShallowCopy 方法来创建一个完整的克隆。这很简单：总共只有几行代码，见上面的演示代码。

请注意，在克隆对象时，“结构”和“类”之间存在很大差异：

• 如果你有一个“结构”，它是一个值类型，所以你可以复制它，内容将被克隆。
• 如果你有一个“类”，它是一个引用类型，所以如果你复制它，你所做的就是复制指向它的指针。要创建真正的克隆，您必须更有创意，并使用一种方法在内存中创建原始对象的另一个副本。
• 错误地克隆对象会导致非常难以确定的错误。在生产代码中，我倾向于实施校验和来仔细检查对象是否已正确克隆，并且没有被另一个引用破坏。可以在发布模式下关闭此校验和。
• 我发现这种方法非常有用：通常，您只想克隆对象的一部分，而不是整个对象。对于修改对象，然后将修改后的副本送入队列的任何用例，这也是必不可少的。

更新

可能使用反射来递归遍历对象图以进行深度复制。 WCF 使用这种技术来序列化一个对象，包括它的所有子对象。诀窍是使用使其可发现的属性注释所有子对象。但是，您可能会失去一些性能优势。

更新

引用独立速度测试（见下面的 cmets）：

我已经使用 Neil 的序列化/反序列化运行了我自己的速度测试 扩展方法，Contango 的 Nested MemberwiseClone，Alex Burtsev 的 基于反射的扩展方法和Aut​​oMapper，100万次 每个。序列化-反序列化最慢，耗时 15.7 秒。然后 AutoMapper 来了，耗时 10.1 秒。更快的是 基于反射的方法，耗时 2.4 秒。到目前为止最快的是 嵌套的 MemberwiseClone，耗时 0.1 秒。归结为性能 与向每个类添加代码以克隆它的麻烦相比。如果性能 Alex Burtsev 的方法不是问题。 ——西蒙·图西

Answer 5

我相信 BinaryFormatter 方法相对较慢（这让我感到惊讶！）。如果某些对象满足 ProtoBuf 的要求，您也许可以对某些对象使用 ProtoBuf .NET。来自 ProtoBuf 入门页面 (http://code.google.com/p/protobuf-net/wiki/GettingStarted)：

有关支持类型的说明：

自定义类：

• 被标记为数据合同
• 有一个无参数的构造函数
• 对于 Silverlight：公开
• 许多常见的原语等
• 单维数组：T[]
• 列表 / IList
• 字典 / IDictionary
• 任何实现 IEnumerable 并具有 Add(T) 方法的类型

The code assumes that types will be mutable around the elected members.因此，不支持自定义结构，因为它们应该是不可变的。

如果您的班级满足这些要求，您可以尝试：

public static void deepCopy<T>(ref T object2Copy, ref T objectCopy)
{
    using (var stream = new MemoryStream())
    {
        Serializer.Serialize(stream, object2Copy);
        stream.Position = 0;
        objectCopy = Serializer.Deserialize<T>(stream);
    }
}

这确实非常快......

编辑：

这是对此进行修改的工作代码（在 .NET 4.6 上测试）。它使用 System.Xml.Serialization 和 System.IO。无需将类标记为可序列化。

public void DeepCopy<T>(ref T object2Copy, ref T objectCopy)
{
    using (var stream = new MemoryStream())
    {
        var serializer = new XS.XmlSerializer(typeof(T));

        serializer.Serialize(stream, object2Copy);
        stream.Position = 0;
        objectCopy = (T)serializer.Deserialize(stream);
    }
}

Answer 6

你可以试试这个

    public static object DeepCopy(object obj)
    {
        if (obj == null)
            return null;
        Type type = obj.GetType();

        if (type.IsValueType || type == typeof(string))
        {
            return obj;
        }
        else if (type.IsArray)
        {
            Type elementType = Type.GetType(
                 type.FullName.Replace("[]", string.Empty));
            var array = obj as Array;
            Array copied = Array.CreateInstance(elementType, array.Length);
            for (int i = 0; i < array.Length; i++)
            {
                copied.SetValue(DeepCopy(array.GetValue(i)), i);
            }
            return Convert.ChangeType(copied, obj.GetType());
        }
        else if (type.IsClass)
        {

            object toret = Activator.CreateInstance(obj.GetType());
            FieldInfo[] fields = type.GetFields(BindingFlags.Public |
                        BindingFlags.NonPublic | BindingFlags.Instance);
            foreach (FieldInfo field in fields)
            {
                object fieldValue = field.GetValue(obj);
                if (fieldValue == null)
                    continue;
                field.SetValue(toret, DeepCopy(fieldValue));
            }
            return toret;
        }
        else
            throw new ArgumentException("Unknown type");
    }

感谢代码项目中的 DetoX83 article。

Answer 7

最好的办法是：

    public interface IDeepClonable<T> where T : class
    {
        T DeepClone();
    }

    public class MyObj : IDeepClonable<MyObj>
    {
        public MyObj Clone()
        {
            var myObj = new MyObj();
            myObj._field1 = _field1;//value type
            myObj._field2 = _field2;//value type
            myObj._field3 = _field3;//value type

            if (_child != null)
            {
                myObj._child = _child.DeepClone(); //reference type .DeepClone() that does the same
            }

            int len = _array.Length;
            myObj._array = new MyObj[len]; // array / collection
            for (int i = 0; i < len; i++)
            {
                myObj._array[i] = _array[i];
            }

            return myObj;
        }

        private bool _field1;
        public bool Field1
        {
            get { return _field1; }
            set { _field1 = value; }
        }

        private int _field2;
        public int Property2
        {
            get { return _field2; }
            set { _field2 = value; }
        }

        private string _field3;
        public string Property3
        {
            get { return _field3; }
            set { _field3 = value; }
        }

        private MyObj _child;
        private MyObj Child
        {
            get { return _child; }
            set { _child = value; }
        }

        private MyObj[] _array = new MyObj[4];
    }

Answer 8

也许你只需要一个浅拷贝，在这种情况下使用Object.MemberWiseClone()。

MemberWiseClone() 的文档中有很好的深度复制策略建议：-

http://msdn.microsoft.com/en-us/library/system.object.memberwiseclone.aspx

Answer 9

    public static object CopyObject(object input)
    {
        if (input != null)
        {
            object result = Activator.CreateInstance(input.GetType());
            foreach (FieldInfo field in input.GetType().GetFields(Consts.AppConsts.FullBindingList))
            {
                if (field.FieldType.GetInterface("IList", false) == null)
                {
                    field.SetValue(result, field.GetValue(input));
                }
                else
                {
                    IList listObject = (IList)field.GetValue(result);
                    if (listObject != null)
                    {
                        foreach (object item in ((IList)field.GetValue(input)))
                        {
                            listObject.Add(CopyObject(item));
                        }
                    }
                }
            }
            return result;
        }
        else
        {
            return null;
        }
    }

这种方式比BinarySerialization 快几倍，并且不需要[Serializable] 属性。

Answer 10

MSDN 文档似乎暗示 Clone 应该执行深层复制，但从未明确说明：

ICloneable 接口包含一个成员 Clone，它旨在支持超出 MemberWiseClone 提供的克隆……MemberwiseClone 方法创建一个浅拷贝……

你会发现我的帖子很有帮助。

http://pragmaticcoding.com/index.php/cloning-objects-in-c/