如果对象的引用变量是超类类型，是否可以访问子类的属性？

Question

I am new to programming and to c# and I just wanna know if there is a way for me to initialize the subclass fields through property if my reference variable is a superclass type.

Example

Character test = new Archer();
test.Damage = 5; // Damage is from the Fighter Class

SuperClass Character

abstract class Character
{
//Superclass common
}

Class Fighter subclass of Character

abstract class Fighter : Character
{
    private int damage
    public int Damage {
        get
        {
            return damage;
        }
        set
        {
            damage = value;
        }
    }
}

Class Archer subclass of Fighter

class Archer : Fighter
{
//stuffs that only archers can do
}

Answer 1

I am new to programming and to c#

Welcome aboard. Let me start by encouraging you to get a good book, take a course, get a tutor, or whatever you do to learn a subject. StackOverflow is explicitly not a tutorial site .

is there is a way for me to initialize the subclass fields through property if my reference variable is a superclass type?

The beginner programmer answer is: no.

If you want to access a property of a more-derived type then the reference you have in hand has to be known to be of that more-derived type.

C# is what we call a "statically typed" language, meaning that there has to be "static" -- that is, known to the compiler -- type information that demonstrates that each expression is valid.

The advanced programmer answer is: yes, but do not do it.

C# has a "dynamic" mode; if you said

dynamic test = new Archer();
test.Damage = 123;

That would work. Do not do this . Two reasons. First, if you turn off static type checking, static type checking is turned off . You could write

dynamic test = new Archer();
test.Damaeg = 123;

and the compiler would allow it, and your program would crash at runtime. Static type checking is there to help you. Use it.

Second, we added dynamic so that people could write C# programs that interact with dynamic languages such as Python and JavaScript. Use it for that, when you need to, not as an end-run around static type checking.

Should I use the most specific class instead?

You should use a specific enough class. In this case, Fighter or Archer would do.

While we are looking at your code, a few other comments:

private int damage
public int Damage {
    get
    {
        return damage;
    }
    set
    {
        damage = value;
    }

That is correct, but that is how you'd write it in C# 1.0. In any version of C# from 3.0 on, you would typically write the much shorter form:

public int Damage { get; set; }

and let the compiler manage the backing field for you.

Consider also: *do you want the Damage property to be settable outside of the class hierarchy? If the answer is "no" then make it a protected set; property. Do you want it to be settable outside of the Fighter class? If no, make it private set; Do you want it to be settable at all after it is initially set? If no, then (in C# 7) omit the set entirely and it will be only settable in the constructor.

Also, this is probably too advanced for you right now, but it may also stop you from going down a bad path. I wrote a series of articles specifically about the problem space you are exploring, and common pitfalls that even advanced programmers fall into. It starts here: https://ericlippert.com/2015/04/27/wizards-and-warriors-part-one/ -- I talk more about abusing dynamic in that series as well.

Answer 2

Answering your question, you can set the value, you just have to cast before:

(test as Archer).Damage = 5; 
//Or
//(test as Fighter).Damage = 5;

Now, if you should do that, check Eric's answer and his blog.