关于虚无的问题

默认情况下，命名空间类型是内部的 默认情况下，包括嵌套类型在内的任何类型成员都是私有的

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.

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:

图形概述(简要总结)

实际上，情况要比这复杂一些。 现在(从c# 7.2开始)，也有private protected，派生类是否在同一个程序集中也很重要。

因此，需要扩展概述:

请参阅有关此主题的c# -dotnet-docs。

因为静态类是密封的，所以它们不能被继承(除非是从Object继承)，所以关键字protected在静态类上是无效的。

对于默认情况，如果你在前面不放访问修饰符，请参见这里: c#类和成员(字段，方法等)的默认可见性?

Non-nested

enum                              public
non-nested classes / structs      internal
interfaces                        internal
delegates in namespace            internal
class/struct member(s)            private
delegates nested in class/struct  private

嵌套:

nested enum      public
nested interface public
nested class     private
nested struct    private

此外，还有seal -关键字，它使类不可继承。 同样，在VB中。NET，关键字有时是不同的，所以这里有一个小抄:

类型或成员可以被同一程序集中的任何其他代码或引用它的另一个程序集中的任何其他代码访问。类型的公共成员的可访问性级别由类型本身的可访问性级别控制。

该类型或成员只能被相同类或结构中的代码访问。

内部类型或成员只能在同一程序集中的文件中访问。

protected类型或成员只能被同一类中的代码或从该类派生的类中的代码访问。 internal:类型或成员可以被同一程序集中的任何代码访问，但不能从另一个程序集中访问。换句话说，内部类型或成员可以从属于同一编译的代码中访问。 protected internal:类型或成员可以由声明它的程序集中的任何代码访问，也可以从另一个程序集中的派生类中访问。

类型或成员可以由在其包含程序集中声明的类派生的类型访问。

受保护的内部成员可从当前程序集或从包含类派生的类型访问。

静态修饰符用于声明静态成员，该成员属于类型本身，而不属于特定对象。静态修饰符可用于声明静态类。在类、接口和结构中，可以向字段、方法、属性、操作符、事件和构造函数添加静态修饰符。

在c# 11中，您还可以使用文件访问修饰符。

文件修饰符将顶级类型的作用域和可见性限制在声明顶级类型的文件中。文件修饰符通常应用于源生成器编写的类型。文件-本地类型为源生成器提供了一种方便的方法来避免所生成类型之间的名称冲突。

// In File1.cs:
file interface IWidget
{
    int ProvideAnswer();
}

file class HiddenWidget
{
    public int Work() => 42;
}

public class Widget : IWidget
{
    public int ProvideAnswer()
    {
        var worker = new HiddenWidget();
        return worker.Work();
    }
}

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)