C# NullReferenceException in unity3d

Question

I have this class:

using UnityEngine;
using System.Collections;

public class Monster1 : MonoBehaviour {

    private GameObject monster_;
    // Use this for initialization

    public Monster1(){
        monster_ = (GameObject)Instantiate(Resources.Load("Monster1"));
        float height = Random.Range(0, Screen.height);
        Vector2 monster1position = new Vector2(Screen.width, height);
        monster1position = camera.ScreenToWorldPoint(monster1position);
        monster_.transform.position = monster1position;
    }
    void Start () {

    }

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

    }

When I am trying to instantiate an object of that class there is a NullReferenceException.

void Start () {
        Monster1 monster1 = new Monster1();

    }

Any idea why this is happening and how can I fix it?

possible duplicate of What is a NullReferenceException and how do I fix it? — Sriram Sakthivel
– Sriram Sakthivel, Commented Mar 2, 2014 at 18:48
@Daniel that was the error, I changed it to Camera.main. Thank you. — Avraam Mavridis
– Avraam Mavridis, Commented Mar 2, 2014 at 18:58

pek · Accepted Answer · 2014-03-03 06:04:42Z

3

2 things: You should never use constructors in your MonoBehaviours. Use Awake instead. So replace

public Monster1(){

with

public void Awake(){

Second, you never instantiate a MonoBehaviour with "new". You need to add it to a game object:

GameObject myGameObject = ...
myGameObject.AddComponemt<Momster1>();

answered Mar 3, 2014 at 6:04

pek

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2 Comments

Avraam Mavridis Over a year ago

thanx for the tips. I tried to do that and I am getting `Cannot implicity convert..."

pek Over a year ago

Could you print the line that contains the error you are getting? I have a feeling you are instantiating a GameObject where you want to instantiate a Monster1

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