Null reference exception when instantiating objects using a for loop.

Getting Started
1

Hello everybody , this is my first post so if I’m not on the right place I apologize.
My project is a shmup and I’m trying to instantiate some ‘fireball’ game objects giving each one of them a different angle. This happens when the prefab for a bigger fireball gets destroyed. The error I keep getting is
NullReferenceException: Object reference not set to an instance of an object
FireballController.ShootFireball (Single angle) (at Assets/Assets/Scripts/Player/FireballController.cs:22)
FireballSpecialController.DestroyFireballSpecial () (at Assets/Assets/Scripts/Player/FireballSpecialController.cs:43)
FireballSpecialController.OnTriggerEnter2D (UnityEngine.Collider2D other) (at Assets/Assets/Scripts/Player/FireballSpecialController.cs:34)

Edit: For some reason I can’t write the square brackets on fireballAngles, but in my code its got those with ‘i’ as the index.

This is my code:

void DestroyFireballSpecial(){
        for (int i = 0; i < fireballAngles.Length; i++) {
            //Instantiate the fireballs accordingly on right position with right rotation
            var fireballObject = Instantiate (fireballs,transform.position,Quaternion.AngleAxis(fireballAngles[i], Vector3.forward)) as GameObject;
            //Set their speed based on angle
            fireballObject.GetComponent<FireballController>().ShootFireball(fireballAngles[i]);
        }
        Destroy(gameObject,0.0f);
    }

And the public function on the fireball:
*_</em></em> <em><em><em>* //Shoot fireball public void ShootFireball(float angle){ rb.velocity = new Vector2(Mathf.Cos(angle*Mathf.Deg2Rad),Mathf.Sin(angle*Mathf.Deg2Rad))*speed; }*</em></em></em> <em><em>_*
Edit: In case you guys want to see the collision function
*_</em></em> <em><em><em>* //Damage enemy void OnTriggerEnter2D(Collider2D other){ if (other.CompareTag("Enemy")){ //Deal damage other.GetComponent<EnemyHealth>().TakeDamage(damage); //Destroy fireball DestroyFireballSpecial(); } }*</em></em></em> <em><em>_*
Thanks in advance :slight_smile:

2

Hi,

Which one is the actual error line of code?
Have you checked if the fireballs prefab has *FireballController-*script attached?

ps. here is info how to insert code into forum post,

3

Its the line on the ShootFireball function that sets the rigidbody’s velocity.
Thanks for the info, it should look alright now . And for the question , yes , each fireball has a FireballController script on it.

4

probably the “rb” variable is not yet set then, can you show the code where you assign it?

1 Like
5

Yea! sure, its on the start() function of each fireball , thats what i use for initializing references

//Initialize variables
    //Publics
    public float speed;
    //Privates
    private int damage;
    private Rigidbody2D rb;
    PlayerController playerController;

    // Use this for initialization
    void Start () {
        //Set damage from player object
        playerController = GameObject.FindWithTag("Player").GetComponent<PlayerController>();
        damage = playerController.attributes.damage;
        rb = GetComponent<Rigidbody2D> ();
    }
    //Shoot fireball
    public void ShootFireball(float angle){
        rb.velocity = new Vector2(Mathf.Cos(angle*Mathf.Deg2Rad),Mathf.Sin(angle*Mathf.Deg2Rad))*speed;
    }
6

Test with Awake() instead of Start() ?

but since you are instantiating it directly (not using pooling?),
in this case you could put that GetComponent inside ShootFireball(), if that fixes it…

1 Like
7

Yes , you are right . Changing Start to Awake fixes the problem.
Thanks!