Unity C# NullReferenceException: Object reference not set to an instance of an object

Question

using UnityEngine;

using System.Collections;

public class GameHandler : MonoBehaviour {

public GameObject playerPrefab;
public GameObject playerCameraPrefab;
public GameObject player;
public GameObject playerCamera;
// Use this for initialization
void Awake () {
    player = Instantiate(playerPrefab,new Vector3(5,1,5),Quaternion.identity) as GameObject;
    playerCamera = Instantiate(playerCameraPrefab,Vector3.up,Quaternion.identity) as GameObject;
}

// Update is called once per frame
void Update () {

}

}

using UnityEngine;

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

public class EarthMagic : MonoBehaviour {

public GameHandler gameHandler;

public GameObject EarthMagicWall;
public PlayerMovement PM;
public UIControls UI;
public Transform spinner;

public List<Transform> circleStones = new List<Transform>();

// Use this for initialization
void Start () {
    //connect to the gameHandler
    gameHandler = GameObject.Find ("WorldHandler").GetComponent("GameHandler") as GameHandler;
    PM = transform.GetComponent("PlayerMovement") as PlayerMovement;
    UI = transform.GetComponent("UIControls") as UIControls;
}

// Update is called once per frame
void Update () {
    if(UI.gamePaused == false) {
        if(Input.GetButtonDown("Channel")) {
            if(PM.isGrounded == true) {
                Vector3 checkPosition = transform.position + (transform.forward * 3);

            //  Debug.DrawRay(transform.position, checkPosition, Color.blue, 20);
            //  Debug.DrawRay(checkPosition, transform.TransformDirection (Vector3.down), Color.red, 20);

                RaycastHit hit;
                if (Physics.Raycast(checkPosition, transform.TransformDirection (Vector3.down), out hit, 5)) {
                    if(hit.collider.name == "Terrain") {
                        Instantiate(EarthMagicWall, hit.point, transform.rotation);
                    }
                }
            }
        }

        if(Input.GetMouseButtonDown(0)) {
            if(circleStones.Count > 0) {
                Transform temp = circleStones[0].transform;
                circleStones.RemoveAt(0);
                temp.parent = null;
                temp.rigidbody.AddForce(Camera.main.transform.up * 20);
            }
        }
        ControlRocks ();
    }
}

void ControlRocks() {
    foreach(Transform circleStone in circleStones) {
        switch(circleStones.Count) {
        case 1: case 2:
            if(circleStones.IndexOf(circleStone) == 1) {
                circleStone.transform.localPosition = new Vector3(0,0, 2); 
            } else {
                circleStone.transform.localPosition = new Vector3(0,0, -2);
            }
            break;
        case 3:
            if(circleStones.IndexOf(circleStone) == 1) {
                circleStone.transform.localPosition = new Vector3(0,0, 2); 
            } else if(circleStones.IndexOf(circleStone) == 2) {
                circleStone.transform.localPosition = new Vector3(Mathf.Sqrt(2),0, (Mathf.Sqrt(2) * -1));
            } else {
                circleStone.transform.localPosition = new Vector3((Mathf.Sqrt(2) * -1),0, (Mathf.Sqrt(2) * -1));
            }
            break;
        case 4:
            if(circleStones.IndexOf(circleStone) == 1) {
                circleStone.transform.localPosition = new Vector3(Mathf.Sqrt(2),0, Mathf.Sqrt(2));  
            } else if(circleStones.IndexOf(circleStone) == 2) {
                circleStone.transform.localPosition = new Vector3(Mathf.Sqrt(2),0, (Mathf.Sqrt(2) * -1));
            } else if(circleStones.IndexOf(circleStone) == 3){
                circleStone.transform.localPosition = new Vector3((Mathf.Sqrt(2) * -1),0, (Mathf.Sqrt(2) * -1));
            } else {
                circleStone.transform.localPosition = new Vector3((Mathf.Sqrt(2) * -1),0, Mathf.Sqrt(2));
            }
            break;
        case 5:
            if(circleStones.IndexOf(circleStone) == 1) {
                circleStone.transform.localPosition = new Vector3(0,0, 2); 
            } else if(circleStones.IndexOf(circleStone) == 2) {
                circleStone.transform.localPosition = new Vector3(1.9f,0, 0.62f);
            } else if(circleStones.IndexOf(circleStone) == 3){
                circleStone.transform.localPosition = new Vector3(1.18f,0, -1.61f);
            } else if(circleStones.IndexOf(circleStone) == 4){
                circleStone.transform.localPosition = new Vector3(-1.18f,0, -1.61f);
            } else {
                circleStone.transform.localPosition = new Vector3(-1.9f,0, 0.62f);
            }
            break;
        }

        Stone stone = circleStone.gameObject.GetComponent("Stone") as Stone;
        if(!stone.isRigid) {
            Rigidbody shardRigidBody = stone.gameObject.AddComponent<Rigidbody>();
            shardRigidBody.mass = 5;
            stone.isRigid = true;
        }
    }
}

}

So the error above occurs at line 63 in EarthMagic. I've solved this type of error before but I don't really understand it this time. This code was working before and I did not change that entire function. I did however start to instantiate my player and camera rather than simply place them in the editor. I'm sure this is the cause of the problem but I don't really know how to fix this. Any ideas?

Answer 1

You have a null element in your list. It is a lot of code and you should debug it yourself, it will help you.

For now you can implement this simple Hack.

foreach(Transform circleStone in circleStones) 
{
    if(circleStone == null)
       continue;       

    switch(circleStones.Count) 
    {
     . 
     .
     .
    }
 }

This code will check for null, if found then it will just skip that element.