C# 访问从 Base class 派生的 class 变量

Question

Given the following:

public class A
{
  public A()
  {
  
  }

}

public class B : A
{
  public int b;
  
  public B()
  {
    
  }
}

public A a = new B();
print(a.b); // I'd like to have many classes that inherit from A, and storing
// one of them on a single variable. Then access the variables that belong to the //derived class

My goal here is to create several classes that inherit from a base class. Then assign one of the classes to a variable (whose type must be of type "A") and access the variables of the derived class. Is it possible?

Answer 1

That is not how inheritance works.

A child can inherit from a parent, but a parent does not inherit from nor have access to anything that is only on the child level.

But you can test to see if it is the subtype, and then explicitly cast, or do the cast while checking.

 A one = new B();
 A two = new A();

 //Check if one is of type B
 if (one.GetType() == typeof(B))
 {
        //Now you can explicitly cast it.
        B newVar = (B)one; 
 }

if (two.GetType() == typeof(B))
{
        //False, will not reach this point
}

//Cast and check at same time to new variable called first
if(one is B first)
{
        //Logic here using first
}

if (two is B second)
{
        /False, will not reach this point
}