how do I extend a class from another script in c# Unity

Question

I'm trying to extend a base class on my player object.
player has damage script that looks like this

using UnityEngine;
using System.Collections;

public class Damage : MonoBehaviour 
{

    public int health = 100;

    public virtual void ReceiveDamage(int damageAmount)
    {
        Debug.Log ("Original");
    }
}

And then the same player has another script like this :

using UnityEngine;
using System.Collections;

public class playerDamage : Damage 
{
    public override void ReceiveDamage(int damageAmount)
    {
        Debug.Log ("Extended");     
    }
}

But when I call the script from a 3rd scrip on another object like this:

var damageScript = collision.gameObject.GetComponent<Damage>();
if( damageScript)
{
    damageScript.ReceiveDamage(damageAmount);
}

the only response to the log is "Original" Shouldn't the child be called and "Extended" written to the log?

Are you sure the instance returned is actually a playerDamage? — Preston Guillot
– Preston Guillot, Commented Oct 23, 2014 at 3:43
Please be aware the Unity tag refers to the Unity application block not the Unity3D game engine. — Dour High Arch
– Dour High Arch, Commented Oct 23, 2014 at 3:50

axwcode · Accepted Answer · 2014-10-23 05:50:32Z

There are several ways to do this. The easiest one is to SendMessage.

collision.gameObject.SendMessage("ReceiveDamage", damageAmount);

Whatever implementation of ReceivedDamage that the collision GameObject has, that will be the one that is called. This is awesome because you don't need to specify the type yourself nor use GetComponent.

Important Extra Information

In any implementation that you choose the key step is to make sure that the right script is attached to the collision.gameObject. If you attach both scripts then you are playing with fire.

To avoid playing with fire please make Damage an abstract class.

public abstract class Damage : MonoBehaviour 
{
    public int health = 100;

    public virtual void ReceiveDamage(int damageAmount)
    {
       Debug.Log ("Original");
    }
}

Abstract will give you the same functionality you want, except that Unity3d won't let you attach Damage to the GameObjects, which is good to avoid mistakes. You will always have the option to have the original ReceiveDamage and the choice to override it on future classes that inherit from Damage, like this:

public class Example : Damage
{
    // This one still has ReceiveDamage but it happens in the base class.
}

or

public class PlayerDamage : Damage 
{
    public override void ReceiveDamage(int damageAmount)
    {
       Debug.Log("Extended");
    }
}

JanR · Accepted Answer · 2014-10-23 06:20:33Z

1

I think when you call this line:

var damageScript = collision.gameObject.GetComponent<Damage>();

It gets the component by name, which in this case would be the Damage script, not the playerDamage script.

In you script it should be:

   var damageScript = collision.gameObject.GetComponent<playerDamage>();
   if( damageScript)
   {
       damageScript.ReceiveDamage(damageAmount);

   }

edited Oct 23, 2014 at 6:20

answered Oct 23, 2014 at 4:33

JanR

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3 Comments

axwcode Over a year ago

You are close, but It instantiates the Damage class is not correct.

JanR Over a year ago

From memory, does it just grab the component by name?

axwcode Over a year ago

Yup, that's what it does.

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