List search gives null

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Hello, i've got an issue here and might need some help with it. First my code: using UnityEngine; using System.Collections;

 public class AttackTowerAimAndShoot : MonoBehaviour {
     
     public float reload = 1F;
     public float firePause = 0.25F;
     public GameObject effect;
     public float amount = 0.001F;
     Transform target;
     Transform[] muzzlePositions;
     Transform turretTurnPoint;
     float newFireTime;
     float newMoveTime;
     private Quaternion rotation;
     private float aimError;
     GameObject projectile;
     public float range = 500F;
     // Use this for initialization
     void Start () {
         Transform muzzle1 = transform.FindChild("MuzzlePos1");
         Transform muzzle2 = transform.FindChild("MuzzlePos2");
         turretTurnPoint = transform.FindChild("Turret");
     }
     
     // Update is called once per frame
     void Update () {
         if (target == null)
             return;
         if (target != null)
         {
             transform.LookAt(target);
             newFireTime = Time.time + (reload * 0.5F);
             if (Time.time >= newFireTime)
             {
                 Fire ();    
             }
         }
         GetTargetEnemy();
     }
     
     void Fire ()
     {
         newFireTime = Time.time + reload;
         newMoveTime = Time.time + firePause;
         //CalculateAimError();
         for (int i = 0; i < muzzlePositions.Length; i++) 
         {
             projectile = Instantiate (Resources.Load("Bullet"), muzzlePositions[i].position, muzzlePositions[i].rotation) as GameObject;
             effect = Instantiate (Resources.Load("FireMuzzle"), muzzlePositions[i].position, muzzlePositions[i].rotation) as GameObject;
         }
     }
     void GetTargetEnemy()
     {
         for (int i = 0; i < StaticVariables.enemies.Count; i++)
         {
             if(StaticVariables.enemies[i].transform == null)
             {
                 StaticVariables.enemies.Remove(StaticVariables.enemies[i]);
                 continue;
             }
             
             if(Vector3.Distance (StaticVariables.enemies[i].position, transform.position) < range)
             {
                 //Debug.Log(Vector3.Distance (StaticVariables.enemies[i].position, transform.position));
                 target = StaticVariables.enemies[i];
                 break;
             }
         }

The problem is with the last part: The void GetTargetEnemy(). I want my towers to search through a list for a target. Though, the enemies[i] always returns 'null', so my towers don't get a new target. I don't understand any of it and I get a NullReferenceException at the Vector3.Distance check all the time. Any help or word of advice is welcome. Thanks in advance!

Answer 1

Answer by whydoidoit · Jan 21, 2013 at 02:38 PM

My guess is that you enemies are getting nulled as they are destroyed.

Given you didn't format your code quite right it's hard to see if your enemy list is

   List<Transform> enemies = new List<Transform>();

Presuming it is then I would suggest that you change you loop to look like this:

   for(int i = StaticVariables.enemies.Count-1; i>= 0; i--)
   {
        if(StaticVariables.enemies[i] == null) //Not .transform
        {
             enemies.RemoveAt(i);
             continue;
        }
        //distance check etcetera

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Malfegor · Jan 21, 2013 at 04:25 PM 0

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Yes, this does make sense, it's still not working propperly, though... My NullReferenceException is gone (and I think I also get the logic behind this For loop) but my 'towers' still don't get a target through... I don't know if this is because I tell the script to look at the distance of the [i] instead of pointing to a Transform object in the first place, but i don't know how to fix this... Is there any way to fix this, or can you give me a hint for another option? Or should i ask this in another question? Anyway: thank you for letting me know the secret behind the NullReference mystery! :D

Answer 2

Answer by Malfegor · Jan 30, 2013 at 08:35 AM

Fixed the problem: I spawned the enemies as Transforms and (I don't know why this happened) they where made null as soon as they entered the list. All i had to do was modify this part:

 public Transform enemy;
 enemy = Instantiate (Resources.Load("FastEnemy"), spawnPoints[i].position, spawnPoints[i].rotation)

To this:

 GameObject newEnemy = Instantiate (Resources.Load("FastEnemy"), spawnPoints[i].position, spawnPoints[i].rotation) as GameObject;
             enemy = newEnemy.transform;

And then add it to the list :)

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List search gives null

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