是否有更好的方式在C＃中创建深层和浅层克隆？
我一直在为一个项目创建对象，并且有一些实例需要为这个对象创建一个深层副本，我想出了使用MemberwiseClone（）的C＃内置函数。 困扰我的问题是每当有一个新的类创建时，我将不得不编写一个像下面的代码一样的函数来获得浅拷贝。可以请某人帮我改进这部分，并给我一个更好的浅拷贝比第二行代码。 谢谢 ：）
浅拷贝：
public static RoomType CreateTwin(RoomType roomType)
{
return (roomType.MemberwiseClone() as RoomType);
}
深度复制：
public static T CreateDeepClone<T>(T source)
{
if (!typeof(T).IsSerializable)
{
throw new ArgumentException("The type must be serializable.", "source");
}
if (Object.ReferenceEquals(source, null))
{
return default(T);
}
IFormatter formatter = new BinaryFormatter();
Stream stream = new MemoryStream();
using (stream)
{
formatter.Serialize(stream, source);
stream.Seek(0, SeekOrigin.Begin);
return (T)formatter.Deserialize(stream);
}
}
MemberwiseClone不是执行深层复制（MSDN）的好选择：
MemberwiseClone方法通过创建一个新对象来创建一个浅表副本，然后将当前对象的非静态字段复制到新对象中。 如果某个字段是值类型，则会执行该字段的逐位副本。 如果一个字段是一个引用类型，则引用被复制，但引用的对象不是 ; 因此，原始对象及其克隆涉及同一个对象。
这意味着如果克隆对象具有引用类型的公共字段或属性，它们会拒绝与原始对象的字段/属性相同的内存位置，因此克隆对象中的每个更改都会反映到初始对象中。 这不是真正的深层复制。
您可以使用BinarySerialization创建一个完全独立的对象实例，请参阅BinaryFormatter类的MSDN页面以获取序列化示例。
示例和测试线束：
使用扩展方法创建给定对象的深层副本：
public static class MemoryUtils
{
/// <summary>
/// Creates a deep copy of a given object instance
/// </summary>
/// <typeparam name="TObject">Type of a given object</typeparam>
/// <param name="instance">Object to be cloned</param>
/// <param name="throwInCaseOfError">
/// A value which indicating whether exception should be thrown in case of
/// error whils clonin</param>
/// <returns>Returns a deep copy of a given object</returns>
/// <remarks>Uses BInarySerialization to create a true deep copy</remarks>
public static TObject DeepCopy<TObject>(this TObject instance, bool throwInCaseOfError)
where TObject : class
{
if (instance == null)
{
throw new ArgumentNullException("instance");
}
TObject clonedInstance = default(TObject);
try
{
using (var stream = new MemoryStream())
{
BinaryFormatter binaryFormatter = new BinaryFormatter();
binaryFormatter.Serialize(stream, instance);
// reset position to the beginning of the stream so
// deserialize would be able to deserialize an object instance
stream.Position = 0;
clonedInstance = (TObject)binaryFormatter.Deserialize(stream);
}
}
catch (Exception exception)
{
string errorMessage = String.Format(CultureInfo.CurrentCulture,
"Exception Type: {0}, Message: {1}{2}",
exception.GetType(),
exception.Message,
exception.InnerException == null ? String.Empty :
String.Format(CultureInfo.CurrentCulture,
" InnerException Type: {0}, Message: {1}",
exception.InnerException.GetType(),
exception.InnerException.Message));
Debug.WriteLine(errorMessage);
if (throwInCaseOfError)
{
throw;
}
}
return clonedInstance;
}
}
NUnit测试：
public class MemoryUtilsFixture
{
[Test]
public void DeepCopyThrowWhenCopyInstanceOfNonSerializableType()
{
var nonSerializableInstance = new CustomNonSerializableType();
Assert.Throws<SerializationException>(() => nonSerializableInstance.DeepCopy(true));
}
[Test]
public void DeepCopyThrowWhenPassedInNull()
{
object instance = null;
Assert.Throws<ArgumentNullException>(() => instance.DeepCopy(true));
}
[Test]
public void DeepCopyThrowWhenCopyInstanceOfNonSerializableTypeAndErrorsDisabled()
{
var nonSerializableInstance = new CustomNonSerializableType();
object result = null;
Assert.DoesNotThrow(() => result = nonSerializableInstance.DeepCopy(false));
Assert.IsNull(result);
}
[Test]
public void DeepCopyShouldCreateExactAndIndependentCopyOfAnObject()
{
var instance = new CustomSerializableType
{
DateTimeValueType =
DateTime.Now.AddDays(1).AddMilliseconds(123).AddTicks(123),
NumericValueType = 777,
StringValueType = Guid.NewGuid().ToString(),
ReferenceType =
new CustomSerializableType
{
DateTimeValueType = DateTime.Now,
StringValueType = Guid.NewGuid().ToString()
}
};
var deepCopy = instance.DeepCopy(true);
Assert.IsNotNull(deepCopy);
Assert.IsFalse(ReferenceEquals(instance, deepCopy));
Assert.That(instance.NumericValueType == deepCopy.NumericValueType);
Assert.That(instance.DateTimeValueType == deepCopy.DateTimeValueType);
Assert.That(instance.StringValueType == deepCopy.StringValueType);
Assert.IsNotNull(deepCopy.ReferenceType);
Assert.IsFalse(ReferenceEquals(instance.ReferenceType, deepCopy.ReferenceType));
Assert.That(instance.ReferenceType.DateTimeValueType == deepCopy.ReferenceType.DateTimeValueType);
Assert.That(instance.ReferenceType.StringValueType == deepCopy.ReferenceType.StringValueType);
}
[Serializable]
internal sealed class CustomSerializableType
{
public int NumericValueType { get; set; }
public string StringValueType { get; set; }
public DateTime DateTimeValueType { get; set; }
public CustomSerializableType ReferenceType { get; set; }
}
public sealed class CustomNonSerializableType
{
}
}
你也可以使用反射来创建对象的副本，这应该是最快的方法，因为序列化也使用反射。
这里有一些代码（测试过）：
public static T DeepClone<T>(this T original, params Object[] args)
{
return original.DeepClone(new Dictionary<Object, Object>(), args);
}
private static T DeepClone<T>(this T original, Dictionary<Object, Object> copies, params Object[] args)
{
T result;
Type t = original.GetType();
Object tmpResult;
// Check if the object already has been copied
if (copies.TryGetValue(original, out tmpResult))
{
return (T)tmpResult;
}
else
{
if (!t.IsArray)
{
/* Create new instance, at this point you pass parameters to
* the constructor if the constructor if there is no default constructor
* or you change it to Activator.CreateInstance<T>() if there is always
* a default constructor */
result = (T)Activator.CreateInstance(t, args);
copies.Add(original, result);
// Maybe you need here some more BindingFlags
foreach (FieldInfo field in t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy | BindingFlags.Instance))
{
/* You can filter the fields here ( look for attributes and avoid
* unwanted fields ) */
Object fieldValue = field.GetValue(original);
// Check here if the instance should be cloned
Type ft = field.FieldType;
/* You can check here for ft.GetCustomAttributes(typeof(SerializableAttribute), false).Length != 0 to
* avoid types which do not support serialization ( e.g. NetworkStreams ) */
if (fieldValue != null && !ft.IsValueType && ft != typeof(String))
{
fieldValue = fieldValue.DeepClone(copies);
/* Does not support parameters for subobjects nativly, but you can provide them when using
* a delegate to create the objects instead of the Activator. Delegates should not work here
* they need some more love */
}
field.SetValue(result, fieldValue);
}
}
else
{
// Handle arrays here
Array originalArray = (Array)(Object)original;
Array resultArray = (Array)originalArray.Clone();
copies.Add(original, resultArray);
// If the type is not a value type we need to copy each of the elements
if (!t.GetElementType().IsValueType)
{
Int32[] lengths = new Int32[t.GetArrayRank()];
Int32[] indicies = new Int32[lengths.Length];
// Get lengths from original array
for (int i = 0; i < lengths.Length; i++)
{
lengths[i] = resultArray.GetLength(i);
}
Int32 p = lengths.Length - 1;
/* Now we need to iterate though each of the ranks
* we need to keep it generic to support all array ranks */
while (Increment(indicies, lengths, p))
{
Object value = resultArray.GetValue(indicies);
if (value != null)
resultArray.SetValue(value.DeepClone(copies), indicies);
}
}
result = (T)(Object)resultArray;
}
return result;
}
}
private static Boolean Increment(Int32[] indicies, Int32[] lengths, Int32 p)
{
if (p > -1)
{
indicies[p]++;
if (indicies[p] < lengths[p])
{
return true;
}
else
{
if (Increment(indicies, lengths, p - 1))
{
indicies[p] = 0;
return true;
}
else
{
return false;
}
}
}
return false;
}
更新
增加了一些代码，现在你可以使用该方法来复制复杂的对象（甚至是具有多个维度的数组）。 请注意，代表仍未实现。
如果你想要一个完整的实现，你需要处理ISerializable接口，这不是很难，但需要一些时间来反映现有的代码。 这是否曾经用于远程实施？
正如sll所建议的那样，使用序列化的解决方案是最简单的，但如果您尝试克隆的类型不可序列化，则不起作用。
Felix K.的代码是一个很好的选择，但我发现了一些问题。 这是修正了我发现的一些问题的修订版本。 我还删除了一些我不需要的功能（例如构造函数参数）。
/// <summary>
/// A DeepClone method for types that are not serializable.
/// </summary>
public static T DeepCloneWithoutSerialization<T>(this T original)
{
return original.deepClone(new Dictionary<object, object>());
}
static T deepClone<T>(this T original, Dictionary<object, object> copies)
{
return (T)original.deepClone(typeof(T), copies);
}
/// <summary>
/// Deep clone an object without using serialisation.
/// Creates a copy of each field of the object (and recurses) so that we end up with
/// a copy that doesn't include any reference to the original object.
/// </summary>
static object deepClone(this object original, Type t, Dictionary<object, object> copies)
{
// Check if object is immutable or copy on update
if (t.IsValueType || original == null || t == typeof(string) || t == typeof(Guid))
return original;
// Interfaces aren't much use to us
if (t.IsInterface)
t = original.GetType();
object tmpResult;
// Check if the object already has been copied
if (copies.TryGetValue(original, out tmpResult))
return tmpResult;
object result;
if (!t.IsArray)
{
result = Activator.CreateInstance(t);
copies.Add(original, result);
// Maybe you need here some more BindingFlags
foreach (var field in t.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy | BindingFlags.Instance))
{
var fieldValue = field.GetValue(original);
field.SetValue(result, fieldValue.deepClone(field.FieldType, copies));
}
}
else
{
// Handle arrays here
var originalArray = (Array)original;
var resultArray = (Array)originalArray.Clone();
copies.Add(original, resultArray);
var elementType = t.GetElementType();
// If the type is not a value type we need to copy each of the elements
if (!elementType.IsValueType)
{
var lengths = new int[t.GetArrayRank()];
var indicies = new int[lengths.Length];
// Get lengths from original array
for (var i = 0; i < lengths.Length; i++)
lengths[i] = resultArray.GetLength(i);
var p = lengths.Length - 1;
/* Now we need to iterate though each of the ranks
* we need to keep it generic to support all array ranks */
while (increment(indicies, lengths, p))
{
var value = resultArray.GetValue(indicies);
if (value != null)
resultArray.SetValue(value.deepClone(elementType, copies), indicies);
}
}
result = resultArray;
}
return result;
}
static bool increment(int[] indicies, int[] lengths, int p)
{
if (p > -1)
{
indicies[p]++;
if (indicies[p] < lengths[p])
return true;
if (increment(indicies, lengths, p - 1))
{
indicies[p] = 0;
return true;
}
}
return false;
}
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