为什么我需要一个通过公共属性公开的私有字段? [英] Why do I need a private field that is exposed via public property?

问题描述

我主要来自 Java 世界.所以，C# 属性看起来不错.

I'm comming from Java world mainly. So, C# properties do look nice.

我知道使用 C# 3.0 或更高版本我可以使用自动属性.我更喜欢它:)

I know that with C# 3.0 or above I can use Automatic Properties. I like it even more :).

我的问题是关于一个(可能较旧的)代码，我可以在其中看到:

My question is about a (maybe older) code where I can see this:

   private int age;

   public int Age {

     get { return age; }
     set { age = value; }     
   }

为什么我需要私有字段年龄?我到底在藏什么?

Why do I need the private field age? What I'm I really hiding here?

我完全理解对 getter 和 setter 的需求.我提到我来自 Java 世界并一直在做这件事.

I completely understand the need for the getter and setter. I mentioned that I'm comming from Java world and doing this all the time.

我确实理解 C# 3.0 或更高版本中的自动属性是语法糖.但也许我的问题有一个更简单的答案.这是否意味着(低于 C# 3.0)该属性没有任何价值.那么它必须从其他字段获取值吗?

I do understand that Automatic Properties in C# 3.0 or above are syntatic sugar. But maybe my question has a simpler answer. Does it means that (bellow C# 3.0) the property doesn't hold any value. So it must get the value from some other field?

推荐答案

旧版本的 C# 没有自动属性，因此您必须像在您的示例中一样声明属性所作用的变量.现在，相同的代码可以表示为:

Older versions of C# didn't have automatic properties, so you had to declare your variables that the properties acted upon like in your example. These days, the same code could be expressed as:

public int Age { get; set; }

我认为这回答了您的问题.但是，如果您要问为什么不直接使用 public int Age；而让程序员直接在字段上设置值?"，那么:

I think that answers your question. However, if you are asking "why not just have public int Age; and let programmers set the value on the field directly?", then:

首先要记住的是，属性访问器被编译成方法.这意味着它具有与仅读取/写入类成员变量不同的 ABI，即使它在语法上看起来与您拥有的相同:

First thing to keep in mind is that property accessors are compiled into methods. This means that it has a different ABI from just reading/writing to a class member variable, even though it may syntactically look the same as if you had:

class Fu {
  public int Age;
}

所以，这意味着，如果在未来的某个时刻，您需要添加一些关于 Age 字段已更改的通知 - 如果您正在使用属性，则可以轻松地将此通知逻辑添加到属性设置器中，而无需打破 ABI.

So, what this means is that if, at some point down the road, you need to add some notification that the Age field has changed - if you are using properties, you can easily add this notification logic to the property setter without breaking ABI.

public int Age {
  get { return age; }
  set { age = value; NotifySomeOtherCode (); }
}

如果您从公共字段开始，那么稍后将其更改为属性将更改 ABI，这对于可能依赖于您的程序集的任何程序都是不利的.所以最好从属性入手.

If you start off with a public field, then later changing it to a property will change the ABI which is bad for any program(s) that may depend on your assembly. So it's better to start off with properties.

希望我说的有道理...

Hopefully I'm making sense...

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