Does Unity support Inheritance and Subclassing?

Question

If I have a few different characters/objects in my game that all share some common behavior, can I use inheritance to centralize the common behavior into a base class? Or do you recommend another approach?

To give a simple example, I might want to have a character controlled by the player, and other characters with similar behavior that are controlled by an AI routine.

If inheritance is possible, do the base class and subclasses go in separate files? Do I only have to attach the relevant subclass file to a particular game object, or the base class file as well?

Finally, is inheritance possible in both C# and UnityScript?

Answer 1

Best Answer

Answer by flaminghairball · Oct 23, 2009 at 08:28 PM

Subclassing (inheritance) is available in the Unity flavor of JavaScript as well as in C#. See MSDN for how to use inheritance in C#. To have an inheritance chain in JavaScript:

Create a new JavaScript

Put in this code:

class MyCoolObject extends MonoBehaviour {
    var myCoolInt : int;
    var myCoolFloat : float
}

Now you have a new class that implements all the methods of MonoBehaviour(such as Update() and FixedUpdate()). If you want to create a subclass of MyCoolObject, just:

class MyCoolerObject extends MyCoolObject {
    var myCoolerInt : int;
    var myCoolerFloat : float;
}

Now if you reference MyCoolerObject in a script, both the cooler variables and the cool variables will show up in the inspector.

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Ricardo · Oct 30, 2009 at 09:02 PM 0

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Fla$$anonymous$$gHairball answers the question quite well - since $$anonymous$$yCoolerObject descends from $$anonymous$$yCoolObject, it already contains all its members - you only need to attach the descendant and you will get the parent's properties and methods.

AngryAnt ♦♦ · Nov 05, 2009 at 03:26 PM 1

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C# does support inheritance in the same way as well, yes.

MountDoomTeam · Dec 30, 2012 at 11:40 AM 0

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about part .4 oh the above answer-

How do you reference $$anonymous$$yCoolerObject class in a script?

Golan2781 · Dec 30, 2012 at 12:34 PM 0

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Seeing how these are derived from $$anonymous$$onobehavior, you'd use them just like every other component - add them to an object in your scene. You can then reference them from other components, on events (like a collision) or if another object uses a method to interface with this object.

The generic GetComponent.() function would be a good start if you want to get into using custom modules.

Chronos-L · May 12, 2013 at 08:21 AM 1

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@newbprofi2, would you kindly explain your opinion?

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Answer 2

Answer by Peter Alexander · Dec 28, 2009 at 05:50 AM

Unity does support subclassing, but it does NOT support dynamic dispatch for "Unity" method calls.

For example:

public class MyBehaviour : MonoBehaviour { private void Start() { Debug.Log("MyBehaviour created"); } }

public class DerivedBehaviour : MyBehaviour
{

If you attach a DerivedBehaviour script to a GameObject, it will NOT call MyBehaviour.Start() on startup. If you want to do that then you have to do it manually:

public class MyBehaviour : MonoBehaviour { private virtual void Start() { Debug.Log("MyBehaviour created"); } }

public class DerivedBehaviour : MyBehaviour
{
    private virtual void Start()
    {
        base.Start();
    }
}

Note that making the methods virtual in the first example would not fix the problem.

This applies to all "Unity" calls (e.g. Awake, Start, Update, LateUpdate, OnLevelLoaded etc.). "Normal" method calls work correctly like you would expect in any .NET app.

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AngryAnt ♦♦ · Jan 04, 2010 at 01:55 PM 3

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The reason why you're seeing this is that Awake, Start etc. are not actually methods on the $$anonymous$$onoBehaviour class, but rather messages sent to derivatives of it. You'll therefore see the same behaviour from Send$$anonymous$$essage use.

Bunny83 · May 03, 2011 at 03:12 PM 9

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That's not true. You have it just a little bit wrong. You should get a CS0621 because virtual methods can't be private! It wouldn't make much sense either. Furthermore you have to override the method in the derived class, otherwise you reimplement it and you would hide the base method. I did what you did but use protected for both methods and override in the derived class and it works as expected.

sacredgeometry · Aug 09, 2011 at 05:22 PM 0

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Thank you so much.

steinbitglis · Sep 27, 2011 at 11:04 AM 0

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I don't have the reputation to vote, but this answer is very confusing. (+1 for comments, if I could)

mark.mckenna · Sep 17, 2012 at 01:02 AM 1

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@Bunny83, your complaint is a bit confusing because it addresses only syntactic problems in the answer and not the core of the answer. C# will toss a compiler error for both of these points, so I think they're pretty self explanatory. -- Also, as a potentially interesting aside, there is a conceptually valid interpretation for a virtual private method (which you correctly state that C# doesn't allow). Consider a situation where your parent class has a private abstract virtual method (still not legal in C#, but legal in C++). This specification dictates to an inheriting class that a function must be implemented for use by the parent; that the parent does not itself supply a default implementation for this function; and that this function need not be exposed for use by inheritors of the inheriting class. Forbidding the virtual private member requires the inheriting class to expose its implementation of the function to further inheritors, which isn't strictly necessary in this case, because the only reference to the v.p. member that should functionally exist already knows that a function of that name is accessible (via its own abstraction version of the member). -- Admittedly obscure, but I thought it interesting when I found out about it.

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Answer 3

Answer by Ricardo · Oct 24, 2009 at 04:10 AM

Every script that you add to an object is itself a subclass of MonoBehavior, and from then on it's .Net all the way down (or up, actually). Here are two examples:

As a really straightforward example, you could take a look at the code for Rock'n'Roll dice. As you can see, there's a DieController MonoBehavior, which contains most of the general code, and then there are some subclasses for the various types of die, which override a few relevant properties.
You could also take a look at the behaviors included in UnitySteer, some of which inherit from a very basic VehicleBehavior and also implement particular interfaces.

In short, any language feature that would apply to a regular .Net class applies to your Unity scripts as well, since they are simply .Net classes.

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Simon-O · Sep 03, 2015 at 08:48 PM 0

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Just to be a pedant, they're not simply .Net classes (I challenge you to get this == null to evaluate to True in stock .Net without some seriously sloppy coding)

Dave-Carlile · Sep 03, 2015 at 09:19 PM 0

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I assume you're referring to Unity's custom == operator? Still .NET :)

Answer 4

I just wanted to add that when using Inheritance for MonoBehaviour objects, the GetComponent() function on the GameObject class will return derived objects as well. This wasn't immediately obvious to me, but is very useful for deriving MonoBehaviours to share functionality and write abstract code in Unity.

Using your scenario, here's a very simple example:

public class CharacterBehaviour : MonoBehaviour { void Start() { CharacterBehaviour behaviour = gameObject.GetComponent<CharacterBehaviour>();

     print("Behaviour Type: " + behaviour.GetType().Name);
 }

public class PlayerCharacterBehaviour : CharacterBehaviour {

public class AICharacterBehaviour : CharacterBehaviour {

}

With a GameObject that has a PlayerCharacterBehaviour attached, you will see:

Behaviour Type: PlayerCharacterBehaviour

With a GameObject that has an AICharacterBehaviour attached, you will see:

Behaviour Type: AICharacterBehaviour

This lets you write generic code against all objects with a CharacterBehaviour attached.

Answer 5

Answer by bill · Feb 06, 2010 at 07:50 AM

Inheriting from GameObject seems to crash unity. It would be nice to do to make it easier to interface with other code.

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yoyo · Dec 24, 2010 at 10:49 PM 3

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In Unity 3.0 GameObject is a sealed class, so you can no longer even attempt to derive from it. The same is true of other internal classes such as $$anonymous$$esh.

Does Unity support Inheritance and Subclassing?

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