NullReferenceException

Unity Engine
1

I get the error “Object reference not set to an instance of an object
Testprog.CastRay ()
(at Assets/TestProg.cs:38)
TestProg.Update () (at Assets/TestProg.cs:19)”

using UnityEngine;
using System.Collections;

public class ColorChanger : MonoBehaviour {

Color selectColor=Color.blue;
public Texture2D blueButton=null,greenButton=null;
//public GameObject red,red2,yellow,yellow2;
// Use this for initialization
void Start () {

}

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

if (Input.GetMouseButtonDown(0)) {
Debug.Log(“Pressed left click, casting ray.”);
CastRay();
}

}

private void OnGUI()
{
if (GUI.Button (new Rect (400, 30, 50, 75), blueButton))
selectColor = Color.blue;

if (GUI.Button (new Rect (450, 30, 50, 75), greenButton))
selectColor = Color.green;
}

void CastRay() {

RaycastHit2D hitInfo = Physics2D.Raycast(Camera.main.ScreenToWorldPoint(Input.mousePosition), Vector2.zero);
if (hitInfo != null) {
Debug.Log (hitInfo.collider.gameObject.name);
}

}

}

I spent a lot of time trying different things, but can’t figure out what is wrong. :frowning:

2

Go to your main camera and change the tag to “MainCamera”. Otherwise, “Camera.main” returns null and you get that error.

1 Like
3

I have MainCamera in my scene.

4

Is it tagged “MainCamera”, though? Would help if we had line numbers. Which line are you getting the error on?

Another thing. “if (hitInfo != null)” isn’t good. It’s just “if (hitInfo)”. RayCast doesn’t return null. So, you could be erroring out in the next line when no collider was hit.

5

I’m thinking the issue is on the line after that, actually. I don’t think “hitInfo != null” is equivalent to a guarantee that hitInfo has valid data - so hitInfo.collider might be null, in which case hitInfo.collider.gameObject would throw that error. You need to check if hitInfo.collider is null, instead. (as in the documentation’s example)

(Sidenote: I was thinking that Physics2D.Raycast worked the same way as Physics.Raycast, until I looked up the documentation in response to your code. It does not work the same - with Physics.Raycast, it returns a bool and passes out RaycastHit as an output parameter.)

6

Thanks. I eventually got it right.

public classClickTest:MonoBehaviour
{

voidStart()
{}// Update is called once per frame
void Update()
{
if(Input.GetMouseButtonDown(0))
{
Debug.Log(“Pressed left click, casting ray.”);
CastRay();}
}

void CastRay()
{
Ray ray =Camera.main.ScreenPointToRay(Input.mousePosition);RaycastHit2D hit =Physics2D.Raycast(ray.origin, ray.direction,Mathf.Infinity);

if(hit)
{
Debug.Log(hit.collider.gameObject.name);
}
}

}