C# accesing non static member in a static function

Question

So I have a function:

List<string> names = new string();

private static void getName(string name)
{
    names.add(name);
}

When I attempt to compile I get a: 'object reference is required for the non-static field' notice. What do I have to do to make this member (names) compatible with getName?

I need it to be non static or converted because I want to put the results into other non static functions and forms.

Answer 1

You need to tell the system which list of names you're interested in. It's part of the state of an object, an instance of the class... but which one? Maybe you've created several instances of the class - maybe you've created no instances of the class. The static method has no visibility of that - so which instance do you want it to fetch the names variable value from?

To put it in another example, suppose we had a class like this:

public class Person
{
    public double MassInGrams { get; set; }
    public double HeightInMetres { get; set; }

    public static double ComputeBodyMassIndex()
    {
        // Which person are we interested in?
    }
}

Person p1 = new Person { MassInGrams = 76203, HeightInMetres = 1.8 };
Person p2 = new Person { MassInGrams = 65000, HeightInMetres = 1.7 };

double bmi = Person.ComputeBodyMassIndex();

What would you expect the result to be? You've asked the Person class to compute "the BMI" but without telling it whose BMI to compute. You need to give it that information.

Some options for your situation:

• Change names to be static instead
• Change the method to be an instance method
• Pass in an instance of the class
• Create an instance of the class, possibly returning it
• Fetch an instance of the class some other way

By the way, that's a very strange method name for something which adds a name. It's also somewhat unconventional...

Answer 2

You need to make names static if you want to use it from inside of a static method:

 // If this is static, you can use it from your static method
 static List<string> names = new List<string>();

The issue is that getName is defined on your type, not on an instance of the type. However, names is defined so each instance of your type gets its own value.