使用 new 和 override 在 DerivedClass 中将 BaseClass 属性更改为只读 [英] Change BaseClass property to readonly in DerivedClass with new and override

问题描述

我有一种情况，我想让普通属性在派生类中使用默认值只读.为此，我通过以下方式使用关键字 new:

I have a situation where I want to make normal property to be readonly in derived class with default value. I am using keyword new for that purpose in the following way:

public abstract class BaseClass
{
    public virtual string SomeInfo { get; set; }
}
public class DerivedClass1 : BaseClass
{
    public new string SomeInfo => "ChildInfo1"; // C# 6.0 equivalent of { get { return "ChildInfo1"; } }
}

它工作正常，并且 new DerivedClass1().SomeInfo 不能分配给 - 它是只读的.我知道可以通过基类访问它:

It works fine, and new DerivedClass1().SomeInfo cannot be assigned to -- it is readonly. I'm aware that one could access it through base class:

BaseClass b1 = new DerivedClass1();
b1.SomeInfo = "ChildInfo1 changed";

我只是想让用户无法意外更改它，并且通过基类它会是故意的，在这种情况下它是可以接受的.

I just want to unable user to change it accidentally, and through base class it would be on purpose in which case it's acceptible.

但是，如果派生类是这样的:

However if Derived class would be like this:

public class DerivedClass2 : BaseClass
{
    public override string SomeInfo => "ChildInfo2";
}

那么这个属性将是可访问的，您似乎可以更改它，但它不会被更改，我想了解为什么?

Then this property would be accessible and you could seemingly change it but it would not be changed, and I would like to understand why?

var d2 = new DerivedClass2();
d2.SomeInfo = "ChildInfo2 changed";
Console.WriteLine(d2.SomeInfo); // output: ChildInfo2

更新:
我添加了新答案作为第三个选项，可能是最好的.

UPDATE:
I have added new answer as third option, probably the best.

推荐答案

在你的基类中你有

public virtual string SomeInfo { get; set; }

这只是一个很好的定义:

It's just a nice definition of:

private string _someInfo;
public string SomeInfo
{
  get {return _someInfo;}
  set {_someInfo = value;}
}

如果您使用 Expression-Bodied 属性覆盖它，您将使用

if you override it with an Expression-Bodied property you override the get property with

public string SomeInfo
{
  get {return "ChildInfo2";}
}

但是您没有覆盖 set 属性，因此您仍然可以设置私有变量，但它不会更改任何其他内容.

But you don't override set property, so you could still set the private variable, but it doesn' change anything else.

如果您查看第一个示例:

if you look on your first example:

BaseClass b1 = new DerivedClass1();
b1.SomeInfo = "ChildInfo1 changed";

发生完全相同的事情，您可以设置属性，因为基类确实有 setter 并设置了一个私有变量，但是如果您尝试输出 SomeProperty 的值，您会看到它没有更改并且仍然是ChildInfo1"

it happens exact the same thing, you could set property, because base class does have setter and sets a private variable, but if you try to output value of SomeProperty, you see, that it is not changed and is still "ChildInfo1"

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