无法通过嵌套类型访问外部类型的非静态成员

Question

I have error

Cannot access a non-static member of outer type 'Project.Neuro' via nested type 'Project.Neuro.Net'

with code like this (simplified):

class Neuro
{
    public class Net
    {
        public void SomeMethod()
        {
            int x = OtherMethod(); // error is here
        }
    }

    public int OtherMethod() // its outside Neuro.Net class
    {
        return 123;  
    }
}

I can move problematic method to Neuro.Net class, but I need this method outside.

Im kind of objective programming newbie.

Thanks in advance.

Answer 1

The problem is that nested classes are not derived classes, so the methods in the outer class are not inherited .

Some options are

1. Make the method static :

    class Neuro { public class Net { public void SomeMethod() { int x = Neuro.OtherMethod(); } } public static int OtherMethod() { return 123; } } 

2. Use inheritance instead of nesting classes:

    public class Neuro // Neuro has to be public in order to have a public class inherit from it. { public static int OtherMethod() { return 123; } } public class Net : Neuro { public void SomeMethod() { int x = OtherMethod(); } } 

3. Create an instance of Neuro :

    class Neuro { public class Net { public void SomeMethod() { Neuro n = new Neuro(); int x = n.OtherMethod(); } } public int OtherMethod() { return 123; } } 

Answer 2

you need to instantiate an object of type Neuro somewhere in your code and call OtherMethod on it, since OtherMethod is not a static method. Whether you create this object inside of SomeMethod , or pass it as an argument to it is up to you. Something like:

// somewhere in the code
var neuroObject = new Neuro();

// inside SomeMethod()
int x = neuroObject.OtherMethod();

alternatively, you can make OtherMethod static, which will allow you to call it from SomeMethod as you currently are.

Answer 3

Even though class is nested within another class, it is still not obvious which instance of outer class talks to which instance of inner class. I could create an instance of inner class and pass it to the another instance of outer class. Therefore, you need specific instance to call this OtherMethod() .

You can pass the instance on creation:

class Neuro
{
    public class Net
    {
        private Neuro _parent;
        public Net(Neuro parent)
        {
         _parent = parent;
        }
        public void SomeMethod()
        {
            _parent.OtherMethod(); 
        }
    }

    public int OtherMethod() 
    {
        return 123;  
    }
}

Answer 4

I think making an instance of outer class in inner class is not a good option because you may executing business logic on outer class constructor. Making static methods or properties is better option. If you insist making an instance of outer class than you should add another parameter to outer class contructor that not to execute business logic.