You've got the same variable in both superclass and subclass. You don't want to do that. Certainly Unity will only present one of them.

Superclass:

    using UnityEngine;
    using System.Collections;

    public class GUIObjectTemplate {

    public Texture2D texture;
    public Rect area;
    public int test = 1;

        public GUIObjectTemplate() {
            //Constructor
        }

        // Use this for initialization
        public virtual void Start () {

        }

        // Update is called once per frame
        public virtual void Update () {

        }

}

The class isn't used at all by itself (maybe I should make it an abstract class). "texture" and "texture_alt" are assigned in the subclass via inspector. "area" is assigned in the constructor of the subclass. To give some perspective on what I'm trying to do, I'm drawing elements (tabs in this case) for a GUI. The specific problem I'm having is in the Draw() method of the subclass. The GUI.DrawTexture() calls crash the program with a NullReferenceException. I think this is caused by the derived class not holding it's instance variables properly.

thanks for the help so far : 3

Subclass:

using UnityEngine;
using System.Collections;

public class GUITab : GUIObjectTemplate {

public Texture2D texture_alt;
public bool selected = false;
public int test1;

    // Use this for initialization
    public override void Start () {
        //Debug.Log(test1);
    }

    // Update is called once per frame
    void Update () {

    }

    //Constructor
    public GUITab(Rect _area) {
        area = _area;
    }


    public void Draw() {
        if (MouseOver()) {
            if (MouseDown()) {selected = true;}         
        }

        if (selected || MouseOver()) {
            GUI.DrawTexture(area, texture);
        }
        else {
            GUI.DrawTexture(area, texture_alt);
        }
    }


    /*These methods are used for simplifying talking to the mouse*/
    bool MouseOver() {
        if (area.Contains(new Vector2(Input.mousePosition.x, Screen.height - Input.mousePosition.y))) {
            return true;
        }
        return false;
    }

    bool MouseDown() {
        if (Input.GetMouseButtonDown(0)) {return true;} return false;
    }

}

also mouse should be Input.GetMouseButtonDown(0) or Input.GetMouseButtonup(0)

The problem is probably because that variable is set on the prefab or gameObject as 0 in the inspector. The assignment that goes with the declaration is some kind of default, and will be the value before it is changed in the inspector.

Usually, the correct thing to do is to change the value in the inspector to 0 (on the prefab or gameObject, as desired).

If you need to assign it from script, make the variable protected, and set the value in Start, like this:

public void Start()
{
   test1 = 0;
}

That should also work for any inheritance scheme as expected.

Here is the full code:

class SuperClass : MonoBehaviour
{
    protected int test1;   

    Start()
    {
        test1 = "12345"; //make it something that is easy to spot for testing
    } 
}

//-----

class SubClass : SuperClass
{
    //do not redefine test1 here!
    public void Start()
    {
        base.Start();
        Debug.Log(test1);
    }
}