C# 中的受保护方法 inheritance

Question

I have a simple C# code written after reading documentation about protected access modifier, but I am recieving a lot of illogical errors. I cant find any solutions to them.

using System;

public class WeaponController
{
    protected void Reload()
    {
        Console.WriteLine("Reload");
    }

    protected virtual void Shoot()
    {

    }
}

public class SMGController : WeaponController
{

    private override void Shoot()
    {
        Console.WriteLine("Shoot");
    }
}

public class Test
{
    public static void Main()
    {
        var test = new SMGController();
        test.Shoot();
        test.Reload();
    }
}

And I am recieving following errors:

prog.cs(19,27): error CS0621: SMGController.Shoot()': virtual or abstract members cannot be private prog.cs(19,27): error CS0507: SMGController.Shoot()': cannot change access modifiers when overriding protected' inherited member WeaponController.Shoot()' prog.cs(10,25): (Location of the symbol related to previous error) Compilation failed: 2 error(s), 0 warnings

If I will change access modifier of Shoot() method in SMGController to protected I recieve even more errors:

prog.cs(30,8): error CS1540: Cannot access protected member WeaponController.Shoot()' via a qualifier of type SMGController'. The qualifier must be of type Test' or derived from it prog.cs(10,25): (Location of the symbol related to previous error) prog.cs(30,8): error CS0122: WeaponController.Shoot()' is inaccessible due to its protection level prog.cs(10,25): (Location of the symbol related to previous error) prog.cs(31,8): error CS1540: Cannot access protected member WeaponController.Reload()' via a qualifier of type SMGController'. The qualifier must be of type Test' or derived from it prog.cs(5,17): (Location of the symbol related to previous error) prog.cs(31,8): error CS0122: WeaponController.Reload()' is inaccessible due to its protection level prog.cs(5,17): (Location of the symbol related to previous error) Compilation failed: 4 error(s), 0 warnings

What is wrong with my code?

Answer 1

You can't call protected methods from outside the class, ie call WeaponController.Shoot from Test .

Also, if you override a protected method, it has to be protected , too.

Obviously, you want Reload and Shoot to be public , so you can call them from Test.Main .

Answer 2

The protected modifier means that only the class itself or a subclass can access Shoot .

You are trying to access it from some other class Test that has no inheritance relation with both SMGController and WeaponController , and such access is forbidden by the protected modifier.

For reference, see https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/protected , especially this line in the first section:

A protected member is accessible within its class and by derived class instances.

You can fix this by making Shoot public . Or if you insist on keeping it protected , then you would need to add a method eg public PublicShoot() that then calls the protected method.