Must declare a body becase it is not marked abstract, extern or partial

Question

Hello all.

I'm a tool, tired and completely out of my depth!!

I have created the following class based on some old code so one has kindly given me. However, I cannae get past the error as described in the title.

The classe is as follows

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Runtime.CompilerServices;

namespace VDSORDAL
{
        public abstract class ObjectComparer<T> : IComparer<T>
        {
            public ObjectComparer(string compareField, string direction);

            private string compareField; 

            public string CompareField 
            { 
                get { return compareField; } 
                set { compareField = value; } 
            }

            public string Direction
            { 
                get { return compareField; } 
                set { compareField = value;} 
            }

            public abstract int Compare(T x, T y);
        }
}

Can someone point out the error in my ways and also give me a brief explanation as to what I am doing wrong and why it is throwing this error?

Any help gratefully received.

Answer 1

You need to add a method body for

public ObjectComparer(string compareField, string direction);

I'd suggest that you do some research into abstract classes. MSDN is a good starting point, but a quick Google search will find you many sources of in depth information.

---

Since the question has been reasonably answered I'll add some extra comments as the code you have been given looks quite broken.

using System.Web;
using System.Runtime.CompilerServices;

These seem to be a odd couple of namespaces to be using in a comparer (especially the second), is this class from a larger file and you haven't got all of it, or is it just left over legacy code?

---

public ObjectComparer(string compareField, string direction);

I'm guessing the constructor should be setting up the properties like this?

public ObjectComparer(string compareField, string direction)
{
    CompareField = compareField;
    Direction = direction;
}

---

public string Direction
{ 
    get { return compareField; } 
    set { compareField = value;} 
}

I think this should have it's own backing field. Seems strange that it will always be the same as CompareField.

---

I don't mean to be rude, but just getting past that error won't make this class work. You really need to understand what it is you are trying to do and how a class like this may help you do it. (If you know all this and just didn't understand the error then I apologise)

Answer 2

You have declared the constructor without a body:

public ObjectComparer(string compareField, string direction);

If you don't want the constructor to do anything, you can still put an empty body ({ }) there.

As a side note, it doesn't make sense to have an abstract class with a public constructor -- the constructor should be protected, because the constructor can only be "called" by classes deriving from it anyway.