Returns NaN when referencing function from another script

Question

So I'm a beginner to unity. My first game i'm making is a top-down shooter game. The enemy chases the player and shoots bullets at him. I have a HealthSystem script that manages all the damages and heals and in it, I have a function called Damage(). Inside my projectile script, I reference the Damage() function in my projectile script. The problem is, when I try to Debug.Log my health, it returns NaN. The function works fine in my Game Handler script though. The GameHandeler and HealthSystem script are both on an empty gameobject and the projectile script is on a bullet prefab.

Ill include my GameHandler, HealthSystem, and Projectile Scripts.

Projectile

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Projectile : MonoBehaviour {
 
     public float speed;
 
     private Transform player;
     private Vector2 target;
 
     public HealthSystem healthSystem;
  
 
     public void Start()
     {
         player = GameObject.FindGameObjectWithTag("Player").transform;
 
         target = new Vector2(player.position.x, player.position.y);
 
         healthSystem = GameObject.Find("GameHandler").GetComponent<HealthSystem>();
 
     }
 
     public void Update()
     {
         transform.position = Vector2.MoveTowards(transform.position, target, speed * Time.deltaTime);
 
             if (transform.position.x == target.x && transform.position.y == target.y)
             {
                 DestroyProjectile();
             }
     }
 
     public void OnTriggerEnter2D(Collider2D other)
     {
             if (other.CompareTag("Player"))
             {
                 DestroyProjectile();
                 healthSystem.Damage(10);
                 Debug.Log("Health: " + healthSystem.GetHealthPercent());
             }
     }
     
      public void DestroyProjectile()
      {
             Destroy(gameObject);
      }
 }

Additional Question: I have to create reference to the script to use healthSystem.Damage(), but in the GameHandeler, I don't have to. Is it because they are on the same object?

GameHandeler

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class GameHandeler : MonoBehaviour {
 
     public Transform pfHealthBar;
     private Transform player;
 
     public void Start()
     {
         player = GameObject.FindGameObjectWithTag("Player").transform;
         HealthSystem healthSystem = new HealthSystem(100);
 
         Transform healthBarTransform = Instantiate(pfHealthBar, new Vector3(0, 1), Quaternion.identity);
         HealthBar healthBar = healthBarTransform.GetComponent<HealthBar>();
         healthBarTransform.transform.parent = player;
         healthBar.Setup(healthSystem);
 
 
         Debug.Log("Health: " + healthSystem.GetHealthPercent());
         healthSystem.Damage(10);
         Debug.Log("Health: " + healthSystem.GetHealthPercent());
         healthSystem.Heal(10);
         Debug.Log("Health: " + healthSystem.GetHealthPercent());
 
     }
 
 }

HealthSystem

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using System;
 
 public class HealthSystem : MonoBehaviour
 {
 
     public event EventHandler OnHealthChanged;
     private int health;
     private int healthMax;
 
     public HealthSystem(int healthMax)
     {
         this.healthMax = healthMax;
         health = healthMax;
     }
 
     public int GetHealth()
     {
         return health;
     }
 
     public float GetHealthPercent()
     {
         return (float)health / healthMax;
     }
 
     public void Damage(int damageAmount)
     {
         health -= damageAmount;
         if (health < 0) health = 0;
         if (OnHealthChanged != null) OnHealthChanged(this, EventArgs.Empty);
     }
 
     public void Heal(int healAmount)
     {
         health += healAmount;
         if (health > healthMax) health = healthMax;
         if (OnHealthChanged != null) OnHealthChanged(this, EventArgs.Empty);
     }
 
 
 }

I got the Projectile script from a blackthornprod tutorial and the HealthSystem + GameHandeler is from a Code Monkey tutorial. Sorry for the lengthy explanation and question. Thanks alot for the help. This has been driving me crazy for two days. alt text

Answer 1

Best Answer

Answer by Klarzahs · Jan 23, 2019 at 10:49 AM

Hi,

Appearently, your healhtMax is not set, which is why on GetHealthPercentage() your current health gets divided by 0 => NaN.

I think this is caused by two different health systems that you create. I cant say for sure, but I assume you already assigned a HealthSystem component to your GameHandler object in the editor, right? So, on starting the game, your GameHandler.Start() function creates a new HealthSystem with HealthSystem healthSystem = new HealthSystem(100);.

The problem now is that you look for the HealthSystem component in your Projectile on Start(). I again assume projectiles are created at runtime, so Projectile.Start() will be called later than GameHandler.Start(). Now, as you assigned a HealthSystem and created a new HealthSystem with your function call, the projectile only assigns the first one. Which has an unset MaxHealth, as only your second HealthSystem was initialized properly.

Takeaway: Don't create something deriving from MonoBehaviour with a "new XYZ()" call. If you are using VisualStudio, it should flag this. If you did not assign a HealthSystem in the Editor, so you dont create two, this is probably still the cause.

You should be using

 HealthSystem hs = AddComponent<HealthSystem>();
 hs.SetMaxHP(100);

instead (or add the component via the editor)

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blubbr · Jan 24, 2019 at 12:15 AM 0

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Im so confused about the solution you put, I understand why its not working but where should i put the code and how do I add HealthSystem as a component. I bet this is a stupid question

Klarzahs blubbr · Jan 24, 2019 at 08:27 AM 0

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You have two options for adding a component. You can either do it

1. in the Editor, by simply drag&drop the HealthSystem script onto the GameHandler object. You then don't call HealthSystem hs = AddComponent<HealthSystem>(); as you already did that by hand. You simply have to set the maxHP in the start function of the GameHandler.
2. By code. As you did not already create a component by dragging/dropping, you'll need to add one dynamically. That is, call HealthSystem hs = AddComponent<HealthSystem>();

Hope this makes it a little bit clearer :)

blubbr Klarzahs · Jan 25, 2019 at 01:08 AM 0

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Thanks so much man! You really helped with this problem!! Your reply didn't fix it, but i guided me toward the solution. My GameHandler object already had the HealthSystem component, so I used HealthSystem healthSystem = GetComponent(); instead of AddComponent. Thank you for such fast replies and good answer :) +rep

Solution I used for anyone who needs it.

As @Klarzahs said, use AddComponent if you don't have the HealthSystem script already on the object.

  private GameObject gameHandeler
         
 public void Start(){
     gameHandeler = GameObject.Find ("GameHandler");
     
         HealthSystem healthSystem = gameHandeler.AddComponent<HealthSystem>();
         
                 healthSystem.healthMax = 100;
                 healthSystem.health = 100;
     }

If you already have the HealthSystem script, use GetComponent

  public void Start(){
         HealthSystem healthSystem = GetComponent<HealthSystem>();
         
             healthSystem.healthMax = 100;
             healthSystem.health = 100;
 }

Basically reworded what he said XD.

Returns NaN when referencing function from another script

Projectile

GameHandeler

HealthSystem

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