vb.net - 如何使派生类可克隆？

Question

我正在尝试创建一个基类和一个派生类，它们都实现了 ICloneable .在我看来，基类 Clone方法应该处理所有基类属性和派生类 Clone方法所有派生类属性并使用基类的 Clone方法。结果是这样的:-

Public Class MyBaseClass
    Implements ICloneable

    Private my_base_var As Integer

    Public Function Clone() As Object Implements System.ICloneable.Clone
        Dim new_base_class As MyBaseClass = New MyBaseClass
        new_base_class.my_base_var = my_base_var
        Return new_base_class
    End Function

End Class

Public Class MySubClass
    Inherits MyBaseClass
    Implements ICloneable

    Private my_sub_var As Integer

    Public Overloads Function Clone() As Object Implements System.ICloneable.Clone
        Dim new_sub_class As MySubClass = CType(MyBase.Clone, MySubClass)    ' (1)
        new_sub_class.my_sub_var = Me.my_sub_var
        Return new_sub_class
    End Function

End Class

这会导致运行时异常 Unable to cast object of type MyBaseClass to type MySubClass在第 (1) 行，我承认这并没有让我感到惊讶。将该行替换为

    Dim new_sub_class As MySubClass = MyBase.Clone

产生了编译错误。在我看来，我需要某种方式来转换 MyBaseClass至 MySubClass为了让基类的成员设置基类的 Clone .一个不太吸引人的替代方法是在子类的 Clone 中复制基类的成员。 .有谁知道在这里做什么？

我看过问题 here但不能将其翻译成 VB.Net。如果给出的解决方案 here有必要，那我就放弃这个想法了。在时间充足的情况下，我计划制作基类 MustInherit ，如果这有什么区别的话。

Answer 1

一个可能的实现可能是这样的:

Public Class MyBaseClass
    Implements ICloneable
    Private my_base_var As Integer = 1

    Public Overridable Function Clone() As Object implements ICloneable.Clone
        Dim theClone = Create()
        theClone.my_base_var = my_base_var
        Return theClone
    End Function

    Protected Overridable Function Create() As MyBaseClass
        Return New MyBaseClass()
    End Function
End Class

Public Class MySubClass
    Inherits MyBaseClass
    Private my_sub_var As Integer = 1

    Public Overrides Function Clone() As Object
        Dim theClone = DirectCast(MyBase.Clone(), MySubClass)
        theClone.my_sub_var = Me.my_sub_var
        Return theClone
    End Function

    Protected Overrides Function Create() As MyBaseClass
        Return New MySubClass()
    End Function
End Class