Object.MemberwiseClone Method

定義

建立目前 Object 的淺層複本 (Shallow Copy)。 Creates a shallow copy of the current Object.

protected object MemberwiseClone ();
傳回

目前 Object 的淺層複本。 A shallow copy of the current Object.

範例

下列範例說明MemberwiseClone方法。The following example illustrates the MemberwiseClone method. 它會定義ShallowCopy方法,以呼叫MemberwiseClone方法來執行淺層複製作業Person物件。It defines a ShallowCopy method that calls the MemberwiseClone method to perform a shallow copy operation on a Person object. 它也會定義DeepCopy執行深層複製作業的方法Person物件。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

在此範例中,Person.IdInfo屬性會傳回IdInfo物件。In this example, the Person.IdInfo property returns an IdInfo object. 如輸出所範例所示,當Person物件會複製藉由呼叫MemberwiseClone方法中,複製Person物件是原始物件,而的獨立複本,不同之處在於它們會共用相同Person.IdInfo物件參考。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. 如此一來,修改 clonePerson.IdInfo屬性變更時,原始物件的Person.IdInfo屬性。As a result, modifying the clone's Person.IdInfo property changes the original object's Person.IdInfo property. 相反地,深層複製作業執行時,複製Person物件,包括其Person.IdInfo可以修改屬性,而不會影響原始物件。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.

備註

MemberwiseClone方法藉由建立新的物件,並再將目前物件的非靜態欄位複製到新的物件建立淺層複本。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. 如果欄位是實值型別,則會執行位元欄位的複本。If a field is a value type, a bit-by-bit copy of the field is performed. 如果欄位是參考型別,則會複製參考,但參考的物件不;因此,原始的物件和其複製品參考相同的物件。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,假設物件 x。 接著,參考物件 A 和 B 參考物件 c。X 的淺層複本建立新物件,X2,也會參考物件 A 和 b。相反地,X 的深層複本建立新物件 X2 A2 和 B2,也就是 A 的複本的新物件和 B.B2,則是參照新物件 C2,也就是一份 c。此範例說明 shallow 和深層複製作業之間的差異。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.

有多種方法來實作深層複製作業,如果藉由執行淺層複製作業MemberwiseClone方法不符合您的需求。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. 這些需求包括下列各項:These include the following:

  • 呼叫類別建構函式複製到使用取自第一個物件的屬性值中建立第二個物件的物件。Call a class constructor of the object to be copied to create a second object with property values taken from the first object. 這是假設物件的值完全由其類別建構函式。This assumes that the values of an object are entirely defined by its class constructor.

  • 呼叫MemberwiseClone建立物件的淺層複本,然後將指派其值會與原始物件的任何屬性或欄位的值是參考型別相同的新物件的方法。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. DeepCopy方法在此範例說明此方法。The DeepCopy method in the example illustrates this approach.

  • 序列化物件是深層複製,然後還原序列化的資料給不同的物件變數。Serialize the object to be deep copied, and then restore the serialized data to a different object variable.

  • 使用反映進行遞迴時,以執行深層複製作業。Use reflection with recursion to perform the deep copy operation.

適用於