Object.MemberwiseClone 方法

定义

创建当前 Object 的浅表副本。Creates a shallow copy of the current Object.

protected:
 System::Object ^ MemberwiseClone();
protected object MemberwiseClone ();
member this.MemberwiseClone : unit -> obj
Protected Function MemberwiseClone () As Object

返回

当前 Object 的浅表副本。A shallow copy of the current Object.

示例

下面的示例演示 MemberwiseClone 方法。The following example illustrates the MemberwiseClone method. 它定义了一个 ShallowCopy 方法,该方法调用 MemberwiseClone 方法对 Person 对象执行浅表复制操作。It defines a ShallowCopy method that calls the MemberwiseClone method to perform a shallow copy operation on a Person object. 它还定义了一个 DeepCopy 方法,该方法对 Person 对象执行深层复制操作。It also defines a DeepCopy method that performs a deep copy operation on a Person object.

using System;

public class IdInfo
{
    public int IdNumber;
    
    public IdInfo(int IdNumber)
    {
        this.IdNumber = IdNumber;
    }
}

public class Person 
{
    public int Age;
    public string Name;
    public IdInfo IdInfo;

    public Person ShallowCopy()
    {
       return (Person) this.MemberwiseClone();
    }

    public Person DeepCopy()
    {
       Person other = (Person) this.MemberwiseClone();
       other.IdInfo = new IdInfo(IdInfo.IdNumber);
       other.Name = String.Copy(Name);
       return other;
    }
}

public class Example
{
    public static void Main()
    {
        // Create an instance of Person and assign values to its fields.
        Person p1 = new Person();
        p1.Age = 42;
        p1.Name = "Sam";
        p1.IdInfo = new IdInfo(6565);

        // Perform a shallow copy of p1 and assign it to p2.
        Person p2 = p1.ShallowCopy();

        // Display values of p1, p2
        Console.WriteLine("Original values of p1 and p2:");
        Console.WriteLine("   p1 instance values: ");
        DisplayValues(p1);
        Console.WriteLine("   p2 instance values:");
        DisplayValues(p2);
        
        // Change the value of p1 properties and display the values of p1 and p2.
        p1.Age = 32;
        p1.Name = "Frank";
        p1.IdInfo.IdNumber = 7878;
        Console.WriteLine("\nValues of p1 and p2 after changes to p1:");
        Console.WriteLine("   p1 instance values: ");
        DisplayValues(p1);
        Console.WriteLine("   p2 instance values:");
        DisplayValues(p2);

        // Make a deep copy of p1 and assign it to p3.
        Person p3 = p1.DeepCopy();
        // Change the members of the p1 class to new values to show the deep copy.
        p1.Name = "George";
        p1.Age = 39;
        p1.IdInfo.IdNumber = 8641;
        Console.WriteLine("\nValues of p1 and p3 after changes to p1:");
        Console.WriteLine("   p1 instance values: ");
        DisplayValues(p1);
        Console.WriteLine("   p3 instance values:");
        DisplayValues(p3);
    }

    public static void DisplayValues(Person p)
    {
        Console.WriteLine("      Name: {0:s}, Age: {1:d}", p.Name, p.Age);
        Console.WriteLine("      Value: {0:d}", p.IdInfo.IdNumber);
    }
}
// The example displays the following output:
//       Original values of p1 and p2:
//          p1 instance values:
//             Name: Sam, Age: 42
//             Value: 6565
//          p2 instance values:
//             Name: Sam, Age: 42
//             Value: 6565
//       
//       Values of p1 and p2 after changes to p1:
//          p1 instance values:
//             Name: Frank, Age: 32
//             Value: 7878
//          p2 instance values:
//             Name: Sam, Age: 42
//             Value: 7878
//       
//       Values of p1 and p3 after changes to p1:
//          p1 instance values:
//             Name: George, Age: 39
//             Value: 8641
//          p3 instance values:
//             Name: Frank, Age: 32
//             Value: 7878
Public Class IdInfo
    Public IdNumber As Integer
    
    Public Sub New(IdNumber As Integer)
        Me.IdNumber = IdNumber
    End Sub
End Class

Public Class Person 
    Public Age As Integer
    Public Name As String
    Public IdInfo As IdInfo

    Public Function ShallowCopy() As Person
       Return DirectCast(Me.MemberwiseClone(), Person)
    End Function

    Public Function DeepCopy() As Person
       Dim other As Person = DirectCast(Me.MemberwiseClone(), Person) 
       other.IdInfo = New IdInfo(IdInfo.IdNumber)
       other.Name = String.Copy(Name)
       Return other
    End Function
End Class

Module Example
   Public Sub Main()
        ' Create an instance of Person and assign values to its fields.
        Dim p1 As New Person()
        p1.Age = 42
        p1.Name = "Sam"
        p1.IdInfo = New IdInfo(6565)

        ' Perform a shallow copy of p1 and assign it to p2.
        Dim p2 As Person = p1.ShallowCopy()

        ' Display values of p1, p2
        Console.WriteLine("Original values of p1 and p2:")
        Console.WriteLine("   p1 instance values: ")
        DisplayValues(p1)
        Console.WriteLine("   p2 instance values:")
        DisplayValues(p2)
        Console.WriteLine()
                
        ' Change the value of p1 properties and display the values of p1 and p2.
        p1.Age = 32
        p1.Name = "Frank"
        p1.IdInfo.IdNumber = 7878
        Console.WriteLine("Values of p1 and p2 after changes to p1:")
        Console.WriteLine("   p1 instance values: ")
        DisplayValues(p1)
        Console.WriteLine("   p2 instance values:")
        DisplayValues(p2)
        Console.WriteLine()
        
        ' Make a deep copy of p1 and assign it to p3.
        Dim p3 As Person = p1.DeepCopy()
        ' Change the members of the p1 class to new values to show the deep copy.
        p1.Name = "George"
        p1.Age = 39
        p1.IdInfo.IdNumber = 8641
        Console.WriteLine("Values of p1 and p3 after changes to p1:")
        Console.WriteLine("   p1 instance values: ")
        DisplayValues(p1)
        Console.WriteLine("   p3 instance values:")
        DisplayValues(p3)
   End Sub
   
    Public Sub DisplayValues(p As Person)
        Console.WriteLine("      Name: {0:s}, Age: {1:d}", p.Name, p.Age)
        Console.WriteLine("      Value: {0:d}", p.IdInfo.IdNumber)
    End Sub
End Module
' The example displays the following output:
'       Original values of m1 and m2:
'          m1 instance values:
'             Name: Sam, Age: 42
'             Value: 6565
'          m2 instance values:
'             Name: Sam, Age: 42
'             Value: 6565
'       
'       Values of m1 and m2 after changes to m1:
'          m1 instance values:
'             Name: Frank, Age: 32
'             Value: 7878
'          m2 instance values:
'             Name: Sam, Age: 42
'             Value: 7878
'       
'       Values of m1 and m3 after changes to m1:
'          m1 instance values:
'             Name: George, Age: 39
'             Value: 8641
'          m3 instance values:
'             Name: Frank, Age: 32
'             Value: 7878

在此示例中,Person.IdInfo 属性返回一个 IdInfo 对象。In this example, the Person.IdInfo property returns an IdInfo object. 如示例中的输出所示,当通过调用 MemberwiseClone 方法克隆 Person 对象时,克隆的 Person 对象是原始对象的独立副本,只不过它们共享相同的 Person.IdInfo 对象引用。As the output from the example shows, when a Person object is cloned by calling the MemberwiseClone method, the cloned Person object is an independent copy of the original object, except that they share the same Person.IdInfo object reference. 因此,修改克隆的 Person.IdInfo 属性会更改原始对象的 Person.IdInfo 属性。As a result, modifying the clone's Person.IdInfo property changes the original object's Person.IdInfo property. 另一方面,执行深层复制操作时,可以修改克隆的 Person 对象(包括其 Person.IdInfo 属性),而不会影响原始对象。On the other hand, when a deep copy operation is performed, the cloned Person object, including its Person.IdInfo property, can be modified without affecting the original object.

注解

MemberwiseClone 方法创建一个浅表副本,方法是创建一个新的对象,然后将当前对象的非静态字段复制到新的对象。The MemberwiseClone method creates a shallow copy by creating a new object, and then copying the nonstatic fields of the current object to the new object. 如果字段是值类型,则执行字段的逐位副本。If a field is a value type, a bit-by-bit copy of the field is performed. 如果字段是引用类型,则会复制引用,但不会复制引用的对象;因此,原始对象及其复本引用相同的对象。If a field is a reference type, the reference is copied but the referred object is not; therefore, the original object and its clone refer to the same object.

例如,假设有一个名为 X 的对象引用对象 A 和 B。对象 B 反过来引用对象 C。X 的浅表副本创建新的对象 X2,后者同时引用对象 A 和 B。与之相比,X 的深层副本会创建一个新的对象 X2,该对象引用作为 A 和 B 的副本的新对象 A2 和 B2,进而引用新的对象 C2,这是 C 的副本。该示例说明了浅层和深层复制操作之间的差异。For example, consider an object called X that references objects A and B. Object B, in turn, references object C. A shallow copy of X creates new object X2 that also references objects A and B. In contrast, a deep copy of X creates a new object X2 that references the new objects A2 and B2, which are copies of A and B. B2, in turn, references the new object C2, which is a copy of C. The example illustrates the difference between a shallow and a deep copy operation.

如果 MemberwiseClone 方法执行的浅层复制操作无法满足您的需要,则可以通过多种方式实现深层复制操作。There are numerous ways to implement a deep copy operation if the shallow copy operation performed by the MemberwiseClone method does not meet your needs. 这些存储包括以下各项:These include the following:

  • 调用要复制的对象的类构造函数,以创建具有从第一个对象获取的属性值的第二个对象。Call a class constructor of the object to be copied to create a second object with property values taken from the first object. 这假设对象的值由其类构造函数完全定义。This assumes that the values of an object are entirely defined by its class constructor.

  • 调用 MemberwiseClone 方法来创建对象的浅表副本,然后将新对象的值与原始对象的值与原始对象的值相同,以将其值作为引用类型的任何属性或字段。Call the MemberwiseClone method to create a shallow copy of an object, and then assign new objects whose values are the same as the original object to any properties or fields whose values are reference types. 该示例中的 DeepCopy 方法说明了这种方法。The DeepCopy method in the example illustrates this approach.

  • 序列化要深层复制的对象,然后将序列化的数据还原到其他对象变量。Serialize the object to be deep copied, and then restore the serialized data to a different object variable.

  • 使用带有递归的反射来执行深层复制操作。Use reflection with recursion to perform the deep copy operation.

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