如何在.NET中对对象进行深层复制（特别是C＃）？ [重复]-Java 学习之路

507

这个问题在这里已有答案：

Deep cloning objects 41答案

我想要一个真正的深层复制品 . 在Java中，这很容易，但是你如何在C＃中做到这一点？

11 回答

我已经看到了一些不同的方法，但我使用了一个通用的实用方法：

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

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

笔记：

您的 class 必须标记为 [Serializable] 才能生效 .
您的源文件必须包含以下代码：

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

回复于 2024-04-24T07:39:02+08:00

266

我wrote a deep object copy extension method，基于递归 "MemberwiseClone" . 它比BinaryFormatter快（ three times faster ），适用于任何对象 . 您不需要默认构造函数或可序列化属性 .

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;
            }
        }
    }

}

回复于 2024-04-24T07:39:02+08:00

以Kilhoffer的解决方案为基础......

使用C＃3.0，您可以创建一个扩展方法，如下所示：

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);
        }
    }
}

它扩展了使用DeepClone方法标记为[Serializable]的任何类

MyClass copy = obj.DeepClone();

回复于 2024-04-24T07:39:02+08:00

你可以使用 Nested MemberwiseClone to do a deep copy . 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（如本页其他答案中所述）快一个数量级 .

请注意 if 您使用 Nested MemberwiseClone for a deep copy ，您必须为类中的每个嵌套级别手动实现ShallowCopy，并使用DeepCopy调用所有所述ShallowCopy方法来创建完整克隆 . 这很简单：总共只有几行，请参阅下面的演示代码 .

以下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，复制结构非常接近.NET能够达到的理论最大速度 .

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执行深层复制，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demo：

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();
    }

同样，请注意 if 您使用 Nested MemberwiseClone for a deep copy ，您必须为类中的每个嵌套级别手动实现ShallowCopy，并使用DeepCopy调用所有所述ShallowCopy方法来创建完整的克隆 . 这很简单：总共只有几行，请参阅上面的演示代码 .

请注意，在克隆对象时，“struct”和“class”之间存在很大差异：

如果您有一个"struct"，它是一个值类型，因此您可以复制它，并且将克隆内容 .
如果你有"class"，它是一个引用类型，所以如果你复制它，你所做的只是将指针复制到它 . 要创建真正的克隆，您必须更具创造性，并使用在内存中创建原始对象的另一个副本的方法 .
错误地克隆对象可能导致非常难以确定的错误 . 在生产环境代码中，我倾向于实现校验和以仔细检查对象是否已正确克隆，并且没有被另一个对它的引用破坏 . 可以在释放模式下关闭此校验和 .
我发现这种方法非常有用：通常，你只想克隆对象的一部分，而不是整个事物 . 对于修改对象，然后将修改后的副本提供到队列中的任何用例，它也是必不可少的 .

Update

可能使用反射来递归遍历对象图以进行深层复制 . WCF使用此技术序列化对象，包括其所有子对象 . 诀窍是使用使其可被发现的属性来注释所有子对象 . 但是，您可能会失去一些性能优势 .

Update

引用独立速度测试（见下面的评论）：

我使用Neil的序列化/反序列化扩展方法，Contango的嵌套MemberwiseClone，Alex Burtsev的基于反射的扩展方法和AutoMapper，每次100万次运行我自己的速度测试 . Serialize-deserialize最慢，耗时15.7秒 . 然后是AutoMapper，耗时10.1秒 . 基于反射的方法要快2.4秒，速度要快得多 . 到目前为止，最快的是嵌套的MemberwiseClone，耗时0.1秒 . 归结为性能与为每个类添加代码以克隆它的麻烦 . 如果表现不是问题，请选择Alex Burtsev的方法 . - Simon Tewsi

回复于 2024-04-24T07:39:02+08:00

552
我相信BinaryFormatter方法相对较慢（这让我感到惊讶！） . 如果符合ProtoBuf的要求，您可以将ProtoBuf .NET用于某些对象 . 从ProtoBuf入门页面（http://code.google.com/p/protobuf-net/wiki/GettingStarted）：

Notes on types supported:

自定义类：
- 被标记为数据 Contract
- 有一个无参数构造函数
- 对于Silverlight：是公开的
- 许多常见的原语等
- 单维数组：T []
- List <T> / IList <T>
- Dictionary <TKey，TValue> / IDictionary <TKey，TValue>
- 任何实现IEnumerable <T>并具有Add（T）方法的类型
该代码假定类型将在当选成员周围变化 . 因此，不支持自定义结构，因为它们应该是不可变的 .

如果你的 class 遇到这些您可以尝试的要求：
```
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);
    }
}
```
哪个确实非常快......

Edit:

这是修改此代码的工作代码（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);
    }
}
```
回复于 2024-04-24T07:39:02+08:00

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DetoX83 article代码项目 .

回复于 2024-04-24T07:39:02+08:00

153

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

有关深层复制策略的文档中有很好的建议 MemberWiseClone() ：

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

回复于 2024-04-24T07:39:02+08:00

最好的方法是：

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];
    }

回复于 2024-04-24T07:39:02+08:00

0

MSDN文档似乎暗示克隆应该执行深层复制，但它从未明确说明：

ICloneable接口包含一个成员Clone，它旨在支持除MemberWiseClone提供的克隆之外的克隆... MemberwiseClone方法创建一个浅拷贝...

你可以找到我的帖子 .

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

回复于 2024-04-24T07:39:02+08:00

-5

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，并且这不需要 [Serializable] 属性 .

回复于 2024-04-24T07:39:02+08:00

我有一个更简单的想法 . 使用LINQ进行新选择 .

public class Fruit
{
  public string Name {get; set;}
  public int SeedCount {get; set;}
}

void SomeMethod()
{
  List<Fruit> originalFruits = new List<Fruit>();
  originalFruits.Add(new Fruit {Name="Apple", SeedCount=10});
  originalFruits.Add(new Fruit {Name="Banana", SeedCount=0});

  //Deep Copy
  List<Fruit> deepCopiedFruits = from f in originalFruits
              select new Fruit {Name=f.Name, SeedCount=f.SeedCount};
}

回复于 2024-04-24T07:39:02+08:00

如何在.NET中对对象进行深层复制（特别是C＃）？ [重复]

11 回答

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