C＃：在类之间传递值（错误CS0120）

Question

In the code below I get an error when I try to call the array from an other class. What went wrong?

Error CS0120: An object reference is required to access non-static member `learningcsharp.Wall.Ar' (CS0120)

using System;

namespace learningcsharp
{
    public class Wall
    {
        private int[] _ar;
        public int[] Ar
        {
            get
            {
                return _ar;
            }
            set
            {
                _ar = value;
            }   
        }

        public void build()
        {
            Ar = new int[] { 0, 0, 1, 0, 0 };
        }
    }

    public class Draw
    {
        public void draw()
        {
            Console.WriteLine (Wall.Ar[1]);   // ERROR CS0120
        }
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            Wall wall = new Wall ();
            wall.build ();
            Draw draw = new Draw ();
            draw.draw ();
        }
    }
}

Answer 1

You need to pass an instance of Wall to draw method as parameter

public class Draw
{
    public void draw(Wall wall)
    {
        Console.WriteLine (wall.Ar[1]);
    }
}

And you can call it like:

 public static void Main (string[] args)
    {
        Wall wall = new Wall ();
        wall.build ();
        Draw draw = new Draw ();
        draw.draw (wall);
    }

Answer 2

The error litterally explained what to do, but here is a example from Jamie Dixon's post: Object in C#

This is from the Offical MSDM page: Creating objects/classes I think that is exactly what you need.

I hope this helps you out.

Good luck

Answer 3

Or simply mark array as static:

private static int[] _ar;

also with property.