C#: constructor of nested class makes “inaccessible due to protection level”

Question

I have this piece of code, and error is generated, just because I haved added into a constructor for its class.

class NestedClass
{
   class A
   {
      A() {}
   }

   class B
   {
       // no constructor
   }

   public static void run()
   {
     A a = new A();  // error
     B b = new B(); // no error
   }
}

And error is:

NestedExample.A is inaccessible due to protection level

Please help me explain this.

Thanks :)

Answer 1

Your constructor is private . Default access modifier for class members is private .

   class A
   {
      A() {}
   }

this is correct implementation

   class A
   {
      public A() {}
   }

Answer 2

Define your constructor as public

public A() { }

Your constructor for class A is private

Private Constructors (C# Programming Guide) - MSDN

Note that if you don't use an access modifier with the constructor it will still be private by default.

---

The reason it is working for B is that you haven't specified any constructor and for default constructor:

Constructor - MSDN

Unless the class is static, classes without constructors are given a public default constructor by the C# compiler in order to enable class instantiation

Answer 3

Define the constructor as public

public class A
{
    public A() {}
}

Answer 4

Your constructor of A is private. It cannot be accessed from outside of A. At the same time, B does not have a consuctor at all and therefore gets a default public constructor.

Answer 5

you need to specify, the default one is private and while in the case of B the compiler provides a public parameterless constructor for you., so you have to specify it for class A

class A
{
    public A() { }
}

Answer 6

Make your nested classes public and the problem will be solved. Your run method is public but the classes you want to use are not public and this gives problems.