我认为这与好的面向对象设计有关。如果您是库的开发人员，则希望隐藏库的内部工作方式。这样，以后就可以修改库的内部工作方式。所以你把你的成员和辅助方法设为私有，只有接口方法是公共的。应该被覆盖的方法应该受到保护。

重新发布这个答案的精彩图表。

以下是维恩图中的所有访问修饰语，从更有限制的到更混杂的: 私人: private protected: c# 7.2新增 内部: 保护: 保护内部: 公众:

public means that it can be accessed by any class in any assembly, which includes the class itself. protected internal means it can be accessed by the class itself (in the class definition), and it can be accessed by any class in the current assembly, but outside of the assembly it can only be accessed by a class that inherits the class, or by the class itself (if it is a partial class) – basically it means internal inside the assembly and protected outside of the assembly. protected means it can only be accessed by the class itself, or accessed by a class that inherits it and that class can be in any assembly internal means it can be accessed by the class itself or by any class in the assembly but can't be accessed at all outside of the assembly unless by the class itself (i.e. it is a partial class) private protected means it can only be accessed by the class itself, or it can be accessed by a class that inherits it and only if that class is in the current assembly. Outside of the assembly, it can only be accessed by the class itself (i.e. it is a partial class) – basically combines internal and protected, or another way of putting it is it's private outside of the assembly and protected inside the assembly. private means that it can only be accessed by the class itself no access modifier: The default access for everything in C# is "the most restricted access you could declare for that member"., which is private for a member / method / nested class in a class and internal for a non-nested class.

In the above text 'accessed' means accessed via an object of the class type, which within a method of the class itself will be the implicit this object, or perhaps the method instantiates an explicit object of the current class type and accesses it through that object. Both are considered to be being accessed by the class itself and therefore the access rules are the same. This also applies to an access being performed from a static method, or when it is a static member / method being accessed, except the access is performed using the class scope and not and object. A member / method of a static class needs to be explicitly made static or it won't compile.

没有嵌套的类可以是公共的，也可以是内部的，默认情况下是内部的。嵌套的类可以是任何访问类型，如果父类是静态的，它就不需要是静态的，它的成员也不需要是静态的。内部类意味着只能实例化它或从当前程序集访问它的静态成员。

您可以在内部或私有嵌套类中拥有公共成员/方法/嵌套类——只有访问说明符(在正在进行的访问的完全限定名称中)低于当前正在进行的访问所需的级别才能阻止访问。

Inheritance in C# is always public unlike C++, which can privately or protectedly inherit, which then changes the access of all classes that then inherit from the class that is inheriting from this class, as well as the access via object / via class scope of type of the class that inheriting privately / protectedly from the class and the class that is inheriting from the class that is inheriting privately / protectedly form the class, and so on. The access is changed such that all access modifiers less restrictive than private or protected are made private and protected respectively.

Private状态表示变量只能被同一类的对象访问。受保护状态将这种访问权限扩展到该类的后代。

“从上表中我们可以看到隐私和受保护之间的区别……我认为两者是一样的....那么这两个单独的命令有什么用呢?

查看MSDN链接了解更多信息

当前访问修饰符的另一种可视化方法(c# 7.2)。希望这个模式能帮助你更容易地记住它 (请按此图片浏览。)

外内

如果你很难记住两个词的访问修饰符，记住由外而内。

Private protected:外部私有(相同程序集)内部受保护(相同程序集) 保内:保外(同一组件)保内(同一组件)

Public -如果你能看到类，那么你也能看到方法

Private -如果你是类的一部分，那么你可以看到这个方法，否则就不能。

Protected -与Private相同，加上所有后代也可以看到该方法。

静态(类)——还记得“类”和“对象”之间的区别吗?忘掉这些吧。“static”也是如此。类是自身的唯一实例。

静态(方法)——无论何时使用这个方法，它都有一个独立于它所属类的实际实例的参考框架。