NullReferenceException using GetComponent(script).function;

Unity Engine
1

So, i have this problem that I really don’t know how to fix.

Basicly, a prefab is istantiated on the game using this script:

var Zombie : Transform;
private var time = 300;
var Spawner : Transform;


function Istantiate()
{
    Instantiate(Zombie, Spawner.position, Quaternion.identity);

}

function Update(){
time +=1;
    
    if(time > 300){
    Istantiate();
    time = 0;
}
}

and it works pretty well, then I have this Enemy AI script

var VitaNemico = 300;
var velocity = 0.3;
var Player : Transform;

function Start () {
Player = GameObject.FindWithTag("Player").transform;
}

function Damage() {

VitaNemico -=10;

}

function Run() {
transform.position = Vector3.MoveTowards(transform.position, Player.position, velocity);
transform.LookAt(Player);
}

function Die() {
Destroy (gameObject);
}

function Update() {
Run();

if (VitaNemico == 0){
Die();
	}
}

And again, it works pretty well.

but then, I use this Gun script:

var hit :  RaycastHit;
public var otherClip: AudioClip;
private var Clip = 30;
private var Ammo = 10;
private var time = 60;
var Ammotex : Texture2D;
var enemy : GameObject;

function Start(){
 enemy = GameObject.FindWithTag("Zombie");
}

function shoot()
{
    if(Input.GetButtonDown("Fire1"))
	if(time > 60)
    {
    	audio.clip = otherClip;
    	audio.Play();
    	Clip -=1;
    	time = 0;
    	
        if(Physics.Raycast(transform.position, transform.forward, hit, range))
        {           
            if(hit.collider.transform.tag == "Zombie")
            {
                return true;
            }
            else
            {
                return false;
            }

        }
    }
}

function Update()
{
	time +=1;
    if(shoot() == true)
    {
        print("HIT");
        enemy.GetComponent(EnemyAI).Damage();
        GameObject.FindWithTag("Player").GetComponent(ScoreManager).AddScore();

    }
    
    if(Clip == 0){
	Reload();
    }
   
}

function Reload()
{
    yield WaitForSeconds (1);
    Clip = 30;
    Ammo =9;
    }
    
    function OnGUI () {
	GUI.Label (Rect (900,60,20,20), Ammotex);
	GUI.Box (Rect (915,60,25,25), Clip.ToString());
	GUI.Box (Rect (940,60,25,25), Ammo.ToString());
}

and It works well too, but when I hit the zombie and it should use:

enemy.GetComponent(EnemyAI).Damage();

there’s a NullReferenceException, what should I do?

2

From my point of view it doesn’t make sense to initialize the enemy variable in Start, because it can be instantiated at all time. What I would do is, that if you hit something, check if it has the Zombie tag. In that case, get the component.

3

Thank you soooo much! I followed your hint and now it works pretty well! Here’s the final script:

var hit :  RaycastHit;
public var otherClip: AudioClip;
private var Clip = 30;
private var Ammo = 10;
private var time = 60;
var Ammotex : Texture2D;
var enemy : GameObject;

function Control(){
 enemy = GameObject.FindWithTag("Zombie");
}

function shoot()
{
    if(Input.GetButtonDown("Fire1"))
	if(time > 60)
    {
    	audio.clip = otherClip;
    	audio.Play();
    	Clip -=1;
    	time = 0;
    	
        if(Physics.Raycast(transform.position, transform.forward, hit, range))
        {           
            if(hit.collider.transform.tag == "Zombie")
            {
                return true;
            }
            else
            {
                return false;
            }

        }
    }
}

function Update(){
Control();
time +=1;
    
    if(shoot() == true)
    {
        print("HIT");
        enemy.GetComponent(EnemyAI).Damage();
        GameObject.FindWithTag("Player").GetComponent(ScoreManager).AddScore();

    }
    
    if(Clip == 0){
	Reload();
    }
   }

function Reload()
{
    yield WaitForSeconds (1);
    Clip = 30;
    Ammo =9;
    }
    
    function OnGUI () {
	GUI.Label (Rect (900,60,20,20), Ammotex);
	GUI.Box (Rect (915,60,25,25), Clip.ToString());
	GUI.Box (Rect (940,60,25,25), Ammo.ToString());
}