Lost reference after method execution

Unity Engine
1

I followed this video on how to create health bars automatically for units. This is my HealthBar class.

using System.Collections;
using UnityEngine;
using UnityEngine.UI;

public class HealthBar : MonoBehaviour
{
   #region SerializeFields

   [SerializeField] private Image foregroundImage;
   [SerializeField] private float updateSpeedInSec = 0.5f;
   [SerializeField] private float positionOffset = 1f;

   #endregion

   #region NonSerializeFields

   private Health health;

   #endregion

   public void SetHealth(Health healthToSet)
   {
       health = healthToSet;
       healthToSet.OnHealthPctChanged += HandleHealthChanged;
   }

   private void HandleHealthChanged(float pct)
   {
       StartCoroutine(ChangeToPct(pct));
   }

   private IEnumerator ChangeToPct(float pct)
   {
       float preChangedPct = foregroundImage.fillAmount;
       float elapsedTime = 0f;

       while (elapsedTime < updateSpeedInSec)
       {
           elapsedTime += Time.deltaTime;
           foregroundImage.fillAmount = Mathf.Lerp(preChangedPct, pct, elapsedTime / updateSpeedInSec);
           yield return null;
       }

       foregroundImage.fillAmount = pct;
   }

   private void LateUpdate()
   {
       var worldToScreenPoint = Camera.main
           .WorldToScreenPoint(health.transform.position + (Vector3) Vector2.up * positionOffset);
       transform.position = worldToScreenPoint;
   }

   private void OnDestroy()
   {
       health.OnHealthPctChanged -= HandleHealthChanged;
   }
}

The problem I’m having is in the lateupdate method, the health field is null, even though in the SetHealth method, it was set properly. I tried logging the health field in the update method, and it was also null.

2

When do you call the Set Health method? It is probably being called after the first lateupdate call. You could add;

if(health == null)
{
    Debug.Log("Health Null in LateUpdate()");
    return;
}

to the start of the LateUpdate method therefore catching it and not trying to run code on a null reference.

3

I tried your suggestion, and it keeps on logging that health null.
So this is my HealthBarController class on a canvas.

using System.Collections.Generic;
using UnityEngine;

public class HealthBarController : MonoBehaviour
{
    #region SerializeFields

    [SerializeField] private HealthBar healthBar;

    #endregion

    #region NonSerializeFields

    private Dictionary<Health, HealthBar> healthBars = new Dictionary<Health, HealthBar>();

    #endregion

    private void Awake()
    {
        Health.OnHealthAdded += AddHealthBar;
        Health.OnHealthRemoved += RemoveHealthBar;
    }

    private void AddHealthBar(Health health)
    {
        if (healthBars.ContainsKey(health)) return;

        var newHealthBar = Instantiate(healthBar, transform);
        healthBars.Add(health, newHealthBar);
        healthBar.SetHealth(health);
    }

    private void RemoveHealthBar(Health health)
    {
        if (!healthBars.ContainsKey(health)) return;

        Destroy(healthBars[health].gameObject);
        healthBars.Remove(health);
    }
}

And this is my Health class on a player character.

using System;
using UnityEngine;

public class Health : MonoBehaviour, IDamageable
{
    #region SerializeFields

    [SerializeField] protected int maxHealth = 100;
  
    public static event Action<Health> OnHealthAdded = delegate {  };
    public static event Action<Health> OnHealthRemoved = delegate {  };
    public event Action<float> OnHealthPctChanged = delegate {  };

    #endregion

    #region NonSerializeFields

    protected int currentHealth;

    #endregion
  
    private void OnEnable()
    {
        currentHealth = maxHealth;
        OnHealthAdded(this);
    }

    public void TakeDamage(int damage)
    {
        currentHealth -= damage;
        float currentHealthPct = (float) currentHealth / maxHealth;
        OnHealthPctChanged(currentHealthPct);
      
        if (currentHealth <= 0)
        {
            Die();
        }
    }

    protected void Die()
    {
        OnHealthRemoved(this);
        Destroy(gameObject);
    }
}