Inheritance is hard. Give me a hand, please?

So, I have this class:

Code (CSharp):

1. public class MobileUnit : Unit {
2.     AidansMovementScript moveConductor;
3.  
4.     void Awake () {
5.         string prefab = gameObject.name;
6.         prefab = prefab.Remove(prefab.IndexOf("("));
7.         prefab = "Sprites/" + prefab;
8.         if (photonView.Owner.ActorNumber == 1) {
9.             GetComponent<SpriteRenderer>().sprite = Resources.Load<Sprite>(prefab + "_white");
10.         }
11.         else if (photonView.Owner.ActorNumber == 2) {
12.             GetComponent<SpriteRenderer>().sprite = Resources.Load<Sprite>(prefab + "_orange");
13.         }
14.         if (this.GetType() == typeof(MobileUnit)) {
15.             if (photonView.IsMine) {
16.                 gameObject.AddComponent<MobileUnit_local>();
17.             }
18.             else {
19.                 gameObject.AddComponent<MobileUnit_remote>();
20.             }
21.             Destroy(this);    
22.         }
23.     }
24.  
25.     private void Start() {
26.         gameState = GameObject.Find("Goliad").GetComponent<GameState>();
27.         MeatReadout = transform.GetChild(0).GetChild(0).GetChild(0).gameObject;
28.         moveConductor = gameObject.GetComponent<AidansMovementScript>();
29.     }
30.  
31.     public virtual void move (Vector3 target, Transform movingTransform = null) {
32.         moveConductor.setDestination(target, movingTransform);
33.     }
34.  
35. }

...and then I have this subordinate class:

Code (CSharp):

1. public class MobileUnit_local : MobileUnit {
2.     AidansMovementScript moveConductor;
3.  
4.     void Start () {
5.         gameState = GameObject.Find("Goliad").GetComponent<GameState>();
6.         MeatReadout = transform.GetChild(0).GetChild(0).GetChild(0).gameObject;
7.         moveConductor = GetComponent<AidansMovementScript>();
8.         gameState.enlivenUnit(gameObject);
9.     }
10.  
11.     public override void activate () {
12.         gameState.activateUnit(gameObject);
13.         gameObject.transform.GetChild(0).gameObject.SetActive(true);
14.         transform.GetChild(0).GetChild(0).GetComponent<RectTransform>().localScale = new Vector3(1,1,1) * (Camera.main.orthographicSize / 5);
15.     }
16.  
17.     public override void deactivate () {
18.         gameObject.transform.GetChild(0).gameObject.SetActive(false);
19.         gameState.deactivateUnit(gameObject);
20.     }
21.  
22. }

... and I call "move" in the subordinate class like so:

Code (CSharp):

1. unit.GetComponent<MobileUnit>().move(destination, optionalTransform);

~~~~~~~~~~~~~~~~~~~~
I get a null reference exception: moveConductor hasn't been defined. After probing around, I discovered that the MobileUnit.move call goes to a MobileUnit class, not a MobileUnit_local class. This happens even if I call this.move() from in the MobileUnit_local Start() function. I'm not great at inheritance, but I'm pretty sure that I should be able to define methods in parent methods and have them implicitly present in child methods.

What am I not understanding?

 

I don't believe this issue has anything to do with inheritance, rather it's just that your

moveConductor

script reference is null.
You're trying to assign it via

GetComponent

:

Code (CSharp):

1. moveConductor = gameObject.GetComponent<AidansMovementScript>();

Does your GameObject have an

AidansMovementScript

component attached onto it?

A different issue I'm seeing involving inheritance here is that you have two

Start

methods.

MobileUnit

defines a

Start

method, and

MobileUnit_local

inherits

MobileUnit

, while also defining its own

Start

method.
If you want to extend the

Start

method from

MobileUnit

, just mark it as

protected virtual

, so that child-classes can access and override it:

Code (CSharp):

1. public class MobileUnit : Unit {
2.    protected virtual void Start() {
3.       //Initialization stuff for MobileUnit here...
4.    }
5. }
6.  
7. public class MobileUnit_local : MobileUnit {
8.    protected override void Start() {
9.       base.Start(); //This calls the Start method in the parent MobileUnit class, so that its initialization logic can also run.
10.  
11.       //Initialization stuff for MobileUnit_local here...
12.    }
13. }

In the same vein, you can also remove the duplicate

moveConductor

reference defined in

MobileUnit_Local

, since there's already one defined in the parent

MobileUnit

anyway, as well as these three duplicate lines in

MobileUnit_Local

's

Start

method...

Code (CSharp):

1. gameState = GameObject.Find("Goliad").GetComponent<GameState>();
2. MeatReadout = transform.GetChild(0).GetChild(0).GetChild(0).gameObject;
3. moveConductor = GetComponent<AidansMovementScript>();

...Because they're already defined in

MobileUnit

's

Start

method, and will run when calling

base.Start()

from

MobileUnit_Local

.

Did you mean to override the

move

method in the

MobileUnit_Local

class? That will do what you're describing here.
Otherwise, this is the intended behaviour. Child-classes do implicitly have the methods of parent-classes, but unless they're overridden, it's the method implementation in the parent class that will run, since the method doesn't actually exist in the child class explicitly.

 

@Vryken Thank you for the thorough response. So, help me understand this: here's another case of inheritance in my project:

Code (CSharp):

1. public class Unit : MonoBehaviourPun {
2.     protected GameState gameState;
3.     protected GameObject MeatReadout;
4.     public int maxMeat = 30;
5.     public int meat = 10;
6.     int meatCost = 10;
7.  
8.     void Awake () {
9.     ...
10.     }
11.    
12.     void Start() {
13.         gameState = GameObject.Find("Goliad").GetComponent<GameState>();
14.         MeatReadout = transform.GetChild(0).GetChild(0).GetChild(0).gameObject;
15.     }
16.  
17.     [PunRPC]
18.     public virtual void die() {
19.         gameState.deadenUnit(gameObject);
20.         GameObject orb = (GameObject)Resources.Load("Orb");
21.         for (; meat > 0; --meat) {
22.             Vector3 place = new Vector3(transform.position.x + Random.Range(-.1f, 0.1f), transform.position.y + Random.Range(-.5f, 0.5f), 0);
23.             GameObject lastOrb = Instantiate(orb, place, transform.rotation);
24.             lastOrb.GetComponent<Rigidbody2D>().AddForce((lastOrb.transform.position - transform.position).normalized * 2);
25.         }
26.         Destroy(gameObject);
27.     }
28. }

Code (CSharp):

1. public class Unit_local : Unit {
2.  
3.     void Start() {
4.         gameState = GameObject.Find("Goliad").GetComponent<GameState>();
5.         gameState.enlivenUnit(gameObject);
6.         MeatReadout = transform.GetChild(0).GetChild(0).GetChild(0).gameObject;
7.     }
8.  
9.     public override void activate () {
10.         gameState.activateUnit(gameObject);
11.         gameObject.transform.GetChild(0).gameObject.SetActive(true);
12.         transform.GetChild(0).GetChild(0).GetComponent<RectTransform>().localScale = new Vector3(1,1,1) * (Camera.main.orthographicSize / 5);
13.     }
14.  
15.     public override void deactivate () {
16.         gameObject.transform.GetChild(0).gameObject.SetActive(false);
17.         gameState.deactivateUnit(gameObject);
18.     }
19.  
20. }

So, same deal as before:

• Virtual method die() in the base class is not overridden in child class.
• die() refers to things that aren't defined in the base class.
• die() called in an instance of child class (not pictured, but I tested it)

This works! What is different here than in the case of move()?

 

SOLVED: I just forget to name moveConductor as a Public or Protected object. Sorry @Vryken for taking your time with this one; I'm sure you understand that sometimes big dialogues are needed to spot small errors. I guess the real mystery is why VS Code didn't highlight the error last night, and Unity allowed the scripts to run.