VB.Net 克隆层次结构，其中父级引用了子级，反之亦然 ->循环引用

Question

情况如下：

Class A 
    Implements ICloneable
    Public Property Children As List(Of Child)
    Public Function Clone() As Object Implements ICloneable.Clone
        Return New A With {
            .Children = Children.Select(Function(c) DirectCast(c.Clone(), Child)).ToList()
        }
    End Function
End Class
Class Child 
    Implements ICloneable
    Public Property Parent As A
    Public Function Clone() As Object Implements ICloneable.Clone
        Return New Child With {
            .Parent = DirectCast(Parent.Clone(), A)
        }
    End Function
End Class

实际对象更为复杂，有几个层次。我不知道如何解决这个问题，因为目前，无论何时在父A类上调用Clone，都会得到一个循环引用。

我该如何避免这种情况？我应该创建自己的Clone函数并传递参数吗？

Answer 1

最简单的解决方案是让Child类根本不克隆Parent属性。当Child克隆自己时，它可以保持Parent属性不变，也可以将其留空。例如：

Class Child 
    Implements ICloneable
    Public Property Parent as A
    Public Function Clone() As Object Implements ICloneable.Clone
        Return New Child() With { .Parent = Me.Parent }
    End Function
End Class

然后，当父A类克隆自己时，它可以设置所有克隆子类的Parent属性，如下所示：

Class A 
    Implements ICloneable
    Public Property Children As List(Of Child)
    Public Function Clone() As Object Implements ICloneable.Clone
        Return New A() With 
            {
            .Children = Me.Children.Select(
                Function(c)
                    Dim result As Child = DirectCast(c.Clone(), Child))
                    result.Parent = Me
                    Return result
                End Function).ToList()
            }
    End Function
End Class

或者，正如您所建议的，您可以创建自己的Clone方法，该方法将父对象作为参数：

Class Child 
    Public Property Parent as A
    Public Function Clone(parent As A) As Object
        Return New Child() With { .Parent = parent }
    End Function
End Class

它不会实现ICloneable，但只要您不需要它与其他类型的ICloneable对象可互换，那就无关紧要了。类似地，您可以重载您的构造函数：

Class Child 
    Public Property Parent as A
    Public Sub New()
    End Sub
    Public Sub New(childToClone As Child, parent As A)
        ' Copy other properties from given child to clone
        Me.Parent = parent
    End Sub
End Class