NullReferenceException Issue

Unity Engine
1

Hey all, I’m having trouble with something that feels like it should be really simple, but I can’t for the life of me track down what’s wrong.

I have two scripts that need to talk to each other. One controls a couple of timers, mouse functionality, and the general management of the game; the other controls the movement of a beam when the mouse is clicked and dragged. I have a “NRE: Object reference not set to an instance of an object” issue on line 35 of Laser.cs, which I feel like is coming from something I didn’t do in LaserMove.cs.

I know the NRE issue is one that pops up a lot on here, and I spent a couple of days crawling through answers here and on everyone’s favorite search engine, but nothing seems to help. Would anyone be able to help me out?

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

public class Laser : MonoBehaviour {
 
    public GameObject laserBeam;

    public float beamTime = 2.0f;
    public float laserCoolDownTime = 10.0f;
    private bool laserAvailable = true;

    public static Vector3 mousePos;
    public static List<Vector3> mousePosList;
 
    void Update ()
    {
        LaserRecord();
    }

    //record the mouse position every frame while LMB is down
    void LaserRecord()
    {
        if (Input.GetMouseButton(0))
        {
            if (laserAvailable)
            {
                beamTime -= Time.deltaTime;
                Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
                RaycastHit hit;

                if (Physics.Raycast(ray, out hit, Mathf.Infinity))
                {
                    mousePosList.Add(hit.point);
                }

                if (beamTime <= 0)
                {
                    beamTime = 0;
                    laserAvailable = false;
                }
            }
        }

        //run a cooldown timer & beam movement after the mouse button is released and the laser is flagged unavailable
        if (!Input.GetMouseButton(0) && !laserAvailable)
        {
            LaserCoolDown();
            laserBeam.GetComponent<LaserMove>().BeamMovement();
        }
    }

    void LaserCoolDown()
    {
        laserCoolDownTime -= Time.deltaTime;
        if (laserCoolDownTime <= 0)
        {
            laserCoolDownTime = 10.0f;
            beamTime = 2.0f;
            laserAvailable = true;
        }
    }

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

public class LaserMove : MonoBehaviour {

    private Vector3 targetPos;
    public int moveSpeed = 3;
    private Vector3 startPos = Laser.mousePos;
    private List<Vector3> coordsArray = Laser.mousePosList;
    public GameObject gameObject;

 
    public void BeamMovement()
    {
        for (int i = 0; i > coordsArray.Count; i++)
        {
            startPos = coordsArray[i];
            targetPos = coordsArray[i + 1];
            float step = moveSpeed*Time.deltaTime;
            gameObject.transform.position = Vector3.MoveTowards(startPos, targetPos, step);
        }
    }
}

Feedback on code is also appreciated. I’m not terribly experienced in programming.

2

Couple of things I noticed:

  1. When you declare ‘List mousePosList’ you need to actually construct it - all you’re doing there currently is telling the compiler what ‘mousePosList’ is. e.g.

List mousePosList = new List< Vector3 >();

  1. In this code ‘for (int i = 0; i > coordsArray.Count; i++)’ it looks like the ‘>’ should be an ‘<’??
3

Thanks! This helped, but now I get the same error at line 49.

4

You could add a check before line 49… i.e

if ( laserBeam != null )
{
laserBeam.GetComponent<LaserMove>().BeamMovement();
}else{
Debug.Log("Laser Beam object not found");
}

Also you should only find the laserMove component once,

if ( laserBeam != null )
{
if ( moveBeam == null )
moveBeam=laserBeam.GetComponent<LaserMove>();

moveBeam.BeamMovement();
}else{
Debug.Log("Laser Beam object not found");
}
5

It doesn’t display the debug check message when added. Here is the new code using your suggestions, and it now states that the same error exists on line 9 of this code:

if (!Input.GetMouseButton(0) && !laserAvailable)
        {
            LaserCoolDown();
            if(laserBeam!=null)
            {
                if (moveBeam == null)
                {
                    moveBeam = laserBeam.GetComponent<LaserMove>();
                    moveBeam.BeamMovement();
                }
                else
                {
                    Debug.Log("Laser Beam Object Not Found!");
                }
            }
        }