VB.net 中的重载与覆盖 [英] Overloads Versus Overrides in VB.net

问题描述

Other1 和 Other2 类的 Previous 属性有什么行为差异.

What are the behavior differences for the Previous Property of Other1 and Other2 Class.

注意Other2的重载Previous属性的返回类型已更改为Other2，而它保持为Base 用于 Other1.

Note than the return type of the overloaded Previous Property of Other2 has been changed to Other2 while it stays as Base for Other1.

Public Class Base
    Private _Previous as Base

    Protected Overridable ReadOnly Property Previous As Base
         Get
             Return _Previous 
         End Get
    End Property

    Public Sub New(Previous as Base)
         _Previous = Previous 
    End Sub
End Class

Public Class Other1
    Inherits Base
    Private _Parent as SomeType

    Protected Overrides ReadOnly Property Previous As Base
         Get
             Return _Parent.Previous.Something
         End Get
    End Property

    Public Sub New(Parent as SomeType)
        MyBase.New(Nothing)
        _Parent = Parent 
    End Sub
End Class

Public Class Other2
    Inherits Base
    Private _Parent as SomeType

    Protected Overloads ReadOnly Property Previous As Other2
         Get
             Return _Parent.Previous.Something
         End Get
    End Property

    Public Sub New(Parent as SomeType)
        MyBase.New(Nothing)
        _Parent = Parent 
    End Sub
End Class

推荐答案

在我对 Jim Wooley 的回答，它看起来像是对重载的属性造成了阴影."我在这篇文章中看到了曙光.

After one of my comment to Jim Wooley's answer, "it look like it Shadows the overloaded property." I saw the light in this article.

因此，Other2 类中的重载更像是遮蔽而不是覆盖.文章中有一个评论特别有启发性:

So, the Overloads in the Other2 class act some more like shadowing than override. There is one of the comments in the article that is particularly instructive :

之所以会产生混淆，是因为关键字重载"并不是 C# 程序员认为的传统 OO 意义上的重载.这是一种特定于 VB.Net 的隐藏类型.在大多数情况下，您实际上可以将关键字 SHADOWS 与 OVERLOADS 交换，并且行为是相同的.不同之处在于当您有一个带有多个重载方法签名的基类时.如果您在子类中声明一个具有匹配名称和 SHADOWS 关键字的方法，它将隐藏基类中该方法的每个重载.如果您改用 OVERLOADS 关键字，它只会隐藏具有相同签名的基类方法.

The confusion arises because the keyword "Overloads" isn't what a C# programmer considers an overload in the traditional OO sense. It's a type of hiding that is specific to VB.Net. You can actually swap the keyword SHADOWS with OVERLOADS in most cases, and the behavior is the same. The difference is when you have a base class with multiple overloaded method signatures. If you declare a method in a subclass with a matching name, and the SHADOWS keyword, it will hide EVERY overload of that method in the base class. If you use the OVERLOADS keyword instead, it will only hide the base class method with an identical signature.

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