答案具体取决于您想要在克隆方法中实现的目标。
如果您想创建当前类的新实例而不实际复制任何属性(听起来您可能有兴趣根据示例代码和描述进行操作),那么简单的解决方案是:
Public Class Foo
Implements ICloneable
Public Function Clone() As Object Implements System.ICloneable.Clone
Return Activator.CreateInstance(Me.GetType)
End Function
End Class
您可以通过在 Bar 中添加消息(或某种调试或输出)来测试是否调用了此函数:
Public Class Bar
Inherits Foo
Public Sub New()
MsgBox("Test")
End Sub
End Class
如果你有Option Strict On
,我强烈推荐,main 中的代码是:
Sub Main()
Dim x As New Bar
Dim y As Bar = DirectCast(x.Clone, Bar)
End Sub
但是,如果您有兴趣从当前类复制成员值,则可以使用会员克隆 http://msdn.microsoft.com/en-us/library/system.object.memberwiseclone.aspx:
Public Class Foo
Implements ICloneable
Public Function Clone() As Object Implements System.ICloneable.Clone
Return Me.MemberwiseClone
End Function
End Class
然而,这只会创建一个浅拷贝,将复制引用,并且不会调用 Bar 上的构造函数。当我们以这种方式使用 MemberwiseClone 时,我们总是添加一个可重写的方法,继承者可以使用该方法来执行克隆后清理:
Public Class Foo
Implements ICloneable
Public Function Clone() As Object Implements System.ICloneable.Clone
Dim oObject As Foo
oObject = DirectCast(Me.MemberwiseClone, Foo)
oObject.PostCloneCleanup()
Return oObject
End Function
Protected Overridable Sub PostCloneCleanup()
End Sub
End Class
Public Class Bar
Inherits Foo
Public Sub New()
MsgBox("Test")
End Sub
Protected Overrides Sub PostCloneCleanup()
MsgBox("PostCloneCleanup")
End Sub
End Class
最后,如果浅复制或处理复制的引用不符合您的喜好,您可以使用一种廉价但非常有效的技巧来执行深复制:使用 BinaryFormatter 进行序列化和反序列化:
Public Function CreateDeepCopy(Of T)(ByVal oRecord As T) As T
If oRecord Is Nothing Then
Return Nothing
End If
If Not oRecord.GetType.IsSerializable Then
Throw New ArgumentException(oRecord.GetType.ToString & " is not serializable")
End If
Dim oFormatter As New System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
Using oStream As IO.MemoryStream = New IO.MemoryStream
oFormatter.Serialize(oStream, oRecord)
oStream.Position = 0
Return DirectCast(oFormatter.Deserialize(oStream), T)
End Using
End Function
这要求类是可序列化的,但这很容易做到。