Instantiated object gives NullReferenceException

Questions & Answers
1

Hi,

We have an event system that spawns Goblins via a GoblinManager like this:

using UnityEngine;
using System.Collections;

public class EventGoblinWave : EventT {
	
	private GoblinManager mManager;

	public EventGoblinWave(GoblinManager aManager) : base("Goblin Wave")
	{		
		mManager = aManager;
		//spawn 3 goblins here
		for (int i = 0; i < 3; i++)
		{
			mManager.SpawnGoblin(new Vector3(5, 47, -7));
		}
	}
	
	public void Update()
	{
		base.Update();
	}
}

now we want to spawn some from an object that is on the scene via the same GoblinManager and we do it like this:

using UnityEngine;
using System.Collections;
public class GoblinHut : MonoBehaviour
{
	public int HitPoints;
	
	private GoblinManager mManager;
	private MainGameLoop mMainGameLoop;
	private float mSpawnTimer;
	
	// Use this for initialization
	void Start () {
		HitPoints = 200;
		mSpawnTimer = -1;
		
		mMainGameLoop = GameObject.Find("MainGameLoop").GetComponent("MainGameLoop") as MainGameLoop;
		mManager = mMainGameLoop.GetGoblinManager();
	}
	
	// Update is called once per frame
	void Update ()
	{
		if (mManager == null)
		{
			mManager = mMainGameLoop.GetGoblinManager();
		}
		
		if (mSpawnTimer >= 2)
		{
			mManager.SpawnGoblin(transform.position);
			mSpawnTimer = 0;
		}
		else
		{
			mSpawnTimer += Time.deltaTime;
		}
	}
	
	public void GetHit(int aHitPointLoss)
	{
		if (HitPoints > 0)
		{
			HitPoints -= aHitPointLoss;
		}
	}
}

when we spawn the object from the GoblinHut via the GoblinManager we get a NullReferenceException when the GoblinManager check if the goblin spawned is dead. It seems it’s because the Start() has not been called when called from the GoblinHut. The thing I don’t understand is that Start() is called when the event spawn them.

Here is the GoblinManager class:

using UnityEngine;
using System.Collections;

public class GoblinManager : MonoBehaviour {
	
	private ArrayList mGoblins;
	public GameObject GoblinPrefab;
	private Object mMainLoop;
	
	public void SetMainLoop(Object aMainLoop)
	{
		mMainLoop = aMainLoop;
	}
	
	// Use this for initialization
	void Start () 
	{
		mGoblins = new ArrayList();
	}
	
	public void SpawnGoblin(Vector3 aPos)
	{
		GameObject newGoblin = Instantiate(GoblinPrefab, aPos, Quaternion.identity) as GameObject;
		newGoblin.active = true;
		if (newGoblin != null)
		{
			mGoblins.Add(newGoblin);
		}
	}
	
	// Update is called once per frame
	public void Update () 
	{
		for (int i = 0; i < mGoblins.Count; i++)
		{
			GameObject obj = (GameObject)mGoblins*;*

  •  	if (obj.active)*

  •  	{*

  •  		EnemyGoblin goblin = obj.GetComponent<EnemyGoblin>();*

  •  		if (goblin != null)*

  •  		{*

  •  			if (goblin.IsDead())*

  •  			{*

_ Destroy((Object)mGoblins*);_
_ mGoblins.RemoveAt(i);_
_ break;_
_ }_
_ }_
_ }_
_ }_
_ }_
_}*_
Thanks for you help

2

Finally, I am getting this error because my loop is trying to access it before it is really created by Unity. I tried to used the “active” property but it is already set to true.