Object Reference Not Set to an instance of an Object

Questions & Answers
1

I have created a class which is supposed to store 4 vairables. A second class is supposed to store a list of the previous class. I have attached the code I have written below.

However, When I run this I get the following error:

NullReferenceException: Object reference not set to an instance of an object
testScript+engagement.addSpawnObj (.spawnOBJ newSpawnOBJ) (at Assets/Scripts/testScript.cs:28)
testScript.CreateRandomEngagement () (at Assets/Scripts/testScript.cs:61)
testScript.Start () (at Assets/Scripts/testScript.cs:46)

Could anyone explain what I have done wrong?

Thanks

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class testScript : MonoBehaviour {

public class spawnOBJ {
	public float cost;
	public int sp;
	public int eType;
	public int num;

	public spawnOBJ (int spawnPoint, int numToBeCreated, int enemyType, float spawnCost) {
		sp = spawnPoint;
		num = numToBeCreated;
		eType = enemyType;
		cost = spawnCost;
	}
}

public class engagement {
	public float totalCost;
	public List<spawnOBJ> spawnOBJlist;
	
	public void addSpawnObj(spawnOBJ newSpawnOBJ) {
		spawnOBJlist.Add (newSpawnOBJ);
		calcTotal ();
	}

	public void calcTotal() {
		totalCost = 0;
		for (int i = 0; i < spawnOBJlist.Count; i++) {
			totalCost += spawnOBJlist*.cost;*

  •   	}*

  •   }*

  • }*

  • //public GameObject spawner;*

  • // Use this for initialization*

  • void Start () {*

  •   CreateRandomEngagement ();*

  • }*

  • // Update is called once per frame*

  • void Update () {*

  • }*

  • void CreateRandomEngagement () {*

  •   spawnOBJ blah = new spawnOBJ (9, 3, 5, 3.0f);*

  •   print ("hello1");*

  •   engagement engage = new engagement ();*

  •   print ("hello2");*

  •   engage.addSpawnObj (blah);*

  •   print (engage.totalCost);*

  • }*
    }

2

You didn’t instantiated your list of spawnOBJ at line 17;
You must instantiate it before you use it:

 public List<spawnOBJ> spawnOBJlist = new List<spawnOBJ>();