Static instance variables in classes with C#

Question

I am trying to teach myself C#. From the book I am using, I created a Color class and a Ball class. Here is the pertinent code:

public class Color
{
    public int Red;
    public int Blue;
    public int Green;
    public int Alpha;

    public Color(int red, int blue, int green, int alpha)
    {
        this.Red = red;
        this.Blue = blue;
        this.Green = green;
        this.Alpha = alpha;
    }
  }

This creates the Color class and allows me to assign values to the standard RGB color spectrum we are used to using the Color constructor.

Then I have a method called GetRed(), also within the Color class, which returns the value I set for Red when I create the color in the constructor.

public int GetRed()
    {
        return Red;
    }

Finally, I have another class called Ball, where I declare an instance variable color1 to get the Red value from the Color class.

class Ball
{
    public int color1 = Color.GetRed();
}

The error I get with the color1 declaration in the Ball class is An object reference is required for the non-static field, method, or property "Color.GetRed()". The fix that Visual Studio suggested was to reference the namespace and the class in the variable declaration, so in my case,public int color1 = Hello_World.Color.GetRed() and to make the color variables I created in my Color class and the GetRed() method static. This fixes my problem, but I'm wondering if there is another way to fix this, where I don't have to make the variables or the method static. I'm sorry if I didn't explain this very well. I'm just starting out in C#, so if you need clarification, please tell me in a response. Thanks.

Answer 1

You should really create a MCVE. Without one we are left guessing. So I guess this is what your books wants you to do:

class Color
{
   // ...
}

class Ball
{
    Color SurfaceColor = new Color(/*...*/);
}

Well, heck, why not, let's go the extra mile. Here is how I would implement the Color - Ball models:

public static class Colors
{   
    public static readonly Color Red   = new Color(255, 0, 0);
    public static readonly Color Green = new Color(0, 255, 0);
    public static readonly Color Blue  = new Color(0, 0, 255);

    public static readonly Color White = new Color(255, 255, 255);
    public static readonly Color Black = new Color(0, 0, 0);
}

public class Color
{
    public int R;
    public int G;
    public int B;

    public Color() : this(Colors.Black) {}

    public Color(Color other) : this(other.R, other.G, other.B) {}

    public Color(int red, int green, int blue)
    {
        R = red;
        G = blue;
        B = blue;
    }
}

public class Ball
{
    public Color SurfaceColor { get; private set; }

    public Ball(Color surfaceColor)
    {
        SurfaceColor = surfaceColor;
    }
}

public class Program
{
    public static void Main()
    {
        Ball blueBall /* huh */ = new Ball(Colors.Blue);
        Ball redBall            = new Ball(Colors.Red);
        Ball maroonBall         = new Ball(new Color(128, 0, 0));
    }
}

Answer 2

public int color1 = Color.GetRed(); <- accessing static method from class Color.

public int color1 = new Color().GetRed(); <- accessing instance method from instance of class Color.

or

public class Ball
{
    private Color _color;

    public Ball(Color color)
    {
        _color = color;
    }

    public int GetColorRedValue()
    {
        return _color.GetRed();
    }
}

and

var color = new Color();
var ball = new Ball(color);

Console.WriteLine(ball.GetColorRedValue()); <- print red color value