为什么虚拟元素必须是 public 并且在 C# 中不能被保护？

Question

我是 C# 新手，目前正在学习 OOP。我正在尝试了解所有这些关键字的工作原理。我正在学习 virtual 关键字，我做了这个 class :

    // Animal class
    public class Animal
    {
        // Class propreties
        public string name { get; set; }
        public int age { get; set; }
        public double happiness { get; set; }

        public static int AnimalCounter = 0;

        // Class constructor
        public Animal(string name_ = "Spotty", int age_ = 4, double happiness_ = 3)
        {
            this.name = name_;
            this.age = age_;
            this.happiness = happiness_;
        } 

        // Virtual methods
        public virtual void Print() { }
        public virtual void Woof () { }
        public virtual void Meow () { }
    }

我不明白的是为什么当我使用虚拟。例如在

public virtual void Print() {}

写的时候报错

protected virtual void Print() {}

据我所知，protected 意味着属性只能在基 class 和所有其他由基 class 构成的 class 中访问=80=].

所以我有一个新的 class 叫做：Dog 它是由基地 class 动物

// Dog class
    public class Dog : Animal
    {
        /* Class Propreties */
        protected double SpotCount_ { get; set; }
        protected double woof_happinessIncrease_ { get; set; }

        // SpotCount = > get and set // GET returns SpotCount // SET 20 if bigger or equal to 20 . SET 0 if less or equal to 0 . otherwise set it to the given value
        public double SpotCount
        {
            get
            {
                return SpotCount_;
            }
            set
            {
                if(value >= 20)
                {
                    SpotCount_ = 20;
                }
                else if(value <= 0)
                {
                    SpotCount_ = 0;
                }
                else
                {
                    SpotCount_ = value;
                }
            }
        }
        // woof_happinessIncrease = > get and set // GET returns woof_happinessIncrease // SET 100 if bigger or equal to 100. SET 0 if less or equal to 0 . otherwise set it to the given value
        public double woof_happinessIncrease
        {
            get
            {
                return woof_happinessIncrease_;
            }
            set
            {
                if(value >= 100)
                {
                    woof_happinessIncrease_ = 100;
                }
                else if(value <= 0)
                {
                    woof_happinessIncrease_ = 0;    
                }
                else
                {
                    woof_happinessIncrease_ = value;
                }
            }
        }

        /* Class Constructor */
        public Dog(string name_ = "Spotty", int age_ = 4, double happiness_ = 3, double SpotCount_=3, double woof_happinessIncrease_=2) : base(name_, age_, happiness_)
        {
            this.SpotCount_ = SpotCount_;
            this.woof_happinessIncrease = woof_happinessIncrease_;
        }

        /* Class Override Methods */
        public override void Print()
        {
            Console.WriteLine(String.Format("Name : {0}", this.name.ToString()));
            Console.WriteLine(String.Format("Age : {0}", this.age.ToString()));
            Console.WriteLine(String.Format("Happiness : {0}", this.happiness.ToString()));
            Console.WriteLine(String.Format("Spot count : {0}", this.SpotCount.ToString()));

            Animal.AnimalCounter++; // Increase the animal counter size by 1 every time we have a new instance of the class Dog.
        }
        public override void Woof()
        {
            // Woof and increase happiness
            this.happiness += woof_happinessIncrease;
            Console.WriteLine(String.Format("{0} woofed. His happiness increased by {1}. His happiness now is : {2}", this.name.ToString(), this.woof_happinessIncrease.ToString(), this.happiness.ToString()));
        }
    }

我使用 override 来覆盖 virtual 的方法在基地 class。但是，如果我在基础 class 中使用 protected for virtual 方法它给我一个错误。

有谁知道为什么？

编译错误：CS0507： 'function1' : 覆盖 'access' 继承成员时无法更改访问修饰符 'function2'

试图在方法覆盖中更改访问规范。

Answer 1

public 虚拟方法应该没有问题。

确保基本方法是 public virtual 并且扩展类（覆盖该方法）将其标记为 public virtual。

public class Animal
{
    public virtual void Print() { }
}

public class Cat : Animal
{
    public override void Print() { Console.WriteLine("Meow"); }
}

不支持：

public class Animal
{
    protected virtual void Print() { }
}

public class Cat : Animal
{
    public override void Print() { Console.WriteLine("Meow"); } // Base is protected, so this doesn't make sense.
}

为什么虚拟元素必须是 public 并且在 C# 中不能被保护？

Why must virtual elements be public and can't be protected in C#?

c#

overriding

virtual

public

protected