C#：基 class 中的受保护方法；无法使用来自另一个 class 的派生 class 对象进行访问

Question

继承自基 class 的 class 是否应该可以访问基 class 的受保护成员？

我正在尝试使用来自另一个 class 的派生 class 的对象访问基 class 的受保护方法，但我收到此错误消息

the base class method is inaccessible due to protection level

我做错了什么？

Program.cs

class Program
{
    static void Main(string[] args)
    {
        DerivedClass dc = new DerivedClass();
        dc.DisplayValue();

    }
}

BaseClass.cs

class BaseClass
{
    private int value = 3;

    protected void DisplayValue()
    {
        Console.WriteLine(this.value);
    }
}

DerivedClass.cs

class DerivedClass : BaseClass{}

Answer 1

DerivedClass 中的代码可以访问 BaseClass 的受保护成员，但只能通过 DerivedClass 类型或子类型的表达式。

您的 Main 函数在 Derived Class 之外，这就是您出现异常的原因。

来自 C# 5 规范的第 3.5.3 节（强调我的）：

When a protected instance member is accessed outside the program text of the class in which it is declared, and when a protected internal instance member is accessed outside the program text of the program in which it is declared, the access must take place within a class declaration that derives from the class in which it is declared. Furthermore, the access is required to take place through an instance of that derived class type or a class type constructed from it.

您可以将代码更改为此代码，例如使用基的受保护函数 class

    public class Program
    {
        public static void Main(string[] args)
        {
            DerivedClass dc = new DerivedClass();
            dc.Display();
        }
    }
    public class BaseClass
    {
        private int value = 3;

        protected void DisplayValue()
        {
            Console.WriteLine(this.value);
        }
    }
    public class DerivedClass : BaseClass
    {
        public void Display()
        {
            DisplayValue();
        }
    }

Answer 2

受保护的成员确实在派生的 classes 中可见。但是在您的示例中，您不会从派生的 class 访问 DisplayValue。您从 Program 访问它， 而不是 从 BaseClass 派生。您需要让该成员 public.

C#：基 class 中的受保护方法；无法使用来自另一个 class 的派生 class 对象进行访问

C#: Protected method in base class; unable to access using derived class object from another class

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