C# inheritance and Object reference

Question

I am new to C# and trying to figure out how inheritance works. I'm getting the following error. Why must the parent parameters be static?

Severity Code Description Project File Line Suppression State Error CS0120 An object reference is required for the non-static field, method, or property 'Rectangle.name' PurrS PATH\Sign.cs 15 Active

Parent:

namespace PurrS.Maps
{
public class Rectangle
{
    protected string name;
    protected int id;
    protected float a;
    protected float b;
    protected float c;
    protected float d;
    protected int posX;
    protected int posY;
    //A----B
    //|    | 
    //C----D

    public Rectangle(string name, int id, float a, float b, float c, float d, int posX, int posY)
    {
        this.name = name;
        this.id = id;
        this.a = a;
        this.b = b;
        this.c = c;
        this.d = d;
    }

}
}

Child:

namespace PurrS.Maps
{

public class Sign : Rectangle
{
    string message;

    public Sign(string message) 
        : base(name, id, a, b, c, d, posX, posY) { //This is where it fails.
        this.message = message;

    }
}
}

Jonesopolis · Accepted Answer · 2016-02-29 21:42:51Z

2

The problem you are seeing stems from the fact that Rectangle has a single constructor - the only way to create an instance of Rectangle is to pass it your 8 parameters.

When you create a Sign that inherits from Rectangle - because it is a Rectangle - it needs to be able to call its Rectangle constructor to be able to successfully construct itself.

Therefore, it needs all the parameters available to call a constructor on Rectangle (you have only one), at the time that its constructor is called.

You can ask for the parameters in Sign, or hardcode them in the Sign constructor:

 public Sign(string message, string name, int id, float a, float b, float c, float d, int posX, int posY) 
     :base(name,id,a,b,c,d,posX,poxY)

 public Sign(string message) : base("a name", 1, 1, 2, 3, 4, 10, 10)

for example.

answered Feb 29, 2016 at 21:42

Jonesopolis

25.4k12 gold badges72 silver badges115 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Evert · Accepted Answer · 2016-02-29 21:35:04Z

2

You must either pass the parameters from a constructor with some more arguments

public Sign(string name, int id, float a, float b, float c, float d, int posX, int posY, string message)
                : base(name, id, a, b, c, d, posX, posY)
            { //This is where it fails.
                this.message = message;

            }

or provide some default fixed values:

        public Sign(string message)
            : base("foo", 1, 0, 0, 0, 0, 1, 1)
        { //This is where it fails.
            this.message = message;

        }

answered Feb 29, 2016 at 21:35

Evert

3542 silver badges8 bronze badges

1 Comment

Theletos Over a year ago

And here I thought the parameters would automagically be passed on to the parent class. Thank you.

lintmouse · Accepted Answer · 2016-02-29 21:33:50Z

1

You need to expand on this:

public Sign(string message) 
    : base(name, id, a, b, c, d, posX, posY) { //This is where it fails.
    this.message = message;
}

To pass the parameters to the base class as follows:

public Sign(string message, string name, int id, etc...) 
    : base(name, id, a, b, c, d, posX, posY) { 
    this.message = message;
}

answered Feb 29, 2016 at 21:33

lintmouse

5,1598 gold badges40 silver badges56 bronze badges

Comments

ProgrammingDude · Accepted Answer · 2016-02-29 21:37:52Z

0

Inheritance means that you child class (the Sign class) will have all of the fields and methods that are in the parent class. Therefore, you can say

public Sign(string name, int id, float a, float b, float c, float d, int posX, int posY)
    {
        this.name = name;
        this.id = id;
        this.a = a;
        this.b = b;
        this.c = c;
        this.d = d;
    }

And not have to declare any of the fields that you are using because they are inherited from the parent class.

answered Feb 29, 2016 at 21:37

ProgrammingDude

5951 gold badge5 silver badges25 bronze badges

Collectives™ on Stack Overflow

C# inheritance and Object reference

4 Answers 4

Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related