[Part 9] NullReferenceException error when using the Done button

[ThatOneGuy]

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I keep getting the error “NullReferenceException: Object reference not set to an instance of an object EnemyStats.OnDestroy () (at Assets/Scripts/Enemy/EnemyStats.cs:68)” when clicking the Done button when trying to return to the menu. (Line 68 is “EnemySpawner es = FindObjectOfType<EnemySpawner>();”

public class EnemyStats : MonoBehaviour
{
    public EnemyScriptableObject enemyData;

    //Current stats
    [HideInInspector]
    public float currentMoveSpeed;
    [HideInInspector]
    public float currentHealth;
    [HideInInspector]
    public float currentDamage;

    public float despawnDistance = 20f;
    Transform player;

    void Awake()
    {
        currentMoveSpeed = enemyData.MoveSpeed;
        currentHealth = enemyData.MaxHealth;
        currentDamage = enemyData.Damage;
    }

    void Start()
    {
        player = FindObjectOfType<PlayerStats>().transform;
    }

    void Update()
    {
        if (Vector2.Distance(transform.position, player.position) >= despawnDistance)
        {
            ReturnEnemy();
        }

    }

    public void TakeDamage(float dmg)
    {
        currentHealth -= dmg;

        if (currentHealth <= 0) 
        {
            Kill();
        }
    }

    public void Kill()
    {
        Destroy(gameObject);
    }

    private void OnCollisionStay2D(Collision2D collision)
    {
        //references the script from collided collider and deal damage using TakeDamage()
        if (collision.gameObject.CompareTag("Player"))
        {
            PlayerStats player = collision.gameObject.GetComponent<PlayerStats>();
            player.TakeDamage(currentDamage); //make sure to use currentDamage instead of weaponData.damage in case any damage multipliers
        }
    }

    private void OnDestroy()
    {
        EnemySpawner es = FindObjectOfType<EnemySpawner>();
        es.OnEnemyKilled();
    }

    void ReturnEnemy()
    {
        //references the EnemySpawner Script
        EnemySpawner es = FindObjectOfType<EnemySpawner>();
        //moves the enemy to a random spawn location
        transform.position = player.position + es.relativeSpawnPoints[Random.Range(0, es.relativeSpawnPoints.Count)].position;
    }
}

[Terence]

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Guy, this happens because OnDestroy() fires when you change scenes, as all the enemies are deleted.

In such a case, the function will not be able to find the EnemySpawner, so es.OnEnemyKilled() cannot fire.

just add a check so that es.OnEnemyKilled() only fires when an enemy spawner can be found (i.e. the es variable is not null):

private void OnDestroy()
{
  EnemySpawner es = FindObjectOfType<EnemySpawner>();
  if(es) es.OnEnemyKilled();
}

[ThatOneGuy]

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Thank you so much for the detailed explanation.

• Terence

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