C# Need Help Finding Where Null Reference Exception Is

Question

I have a script that generates a rope down the y axis. For some reason I'm getting a null reference exception and I can't figure out where it's coming from. When I click on it sends me to random lines on my code. Any help would be appreciated.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 public class RopeController : MonoBehaviour
 {
     public GameObject fragmentPrefab;
     
     public  List<GameObject> fragments = new List<GameObject>();
     private Vector3 interval = new Vector3(0f, -0.5f, 0f);
 
     private float[] xPositions;
     private float[] yPositions;
     private float[] zPositions;
     
     private CatmullRomSpline splineX;
     private CatmullRomSpline splineY;
     private CatmullRomSpline splineZ;
     
     private int splineFactor = 4;
     
     void Start()
     {
 
     }
     
     void Update()
     {
         Vector3 position = transform.position;
         
         for (int i = 0; i < (int)gameObject.transform.position.y; i++) {
         if(fragments.Count <= (int)gameObject.transform.position.y){
             fragments.Add(null);
             fragments[i] = (GameObject) Instantiate(fragmentPrefab, position, Quaternion.identity);
             fragments[i].transform.parent = transform;
             
             SpringJoint joint = fragments[i].GetComponent<SpringJoint>();
             if (i > 0) {
                 joint.connectedBody = fragments[i - 1].rigidbody;
             }
             
             position += interval;
             }
         }
         
         LineRenderer renderer = GetComponent<LineRenderer>();
         renderer.SetVertexCount((fragments.Count - 1) * splineFactor + 1);
         
         xPositions = new float[fragments.Count];
         yPositions = new float[fragments.Count];
         zPositions = new float[fragments.Count];
         
         splineX = new CatmullRomSpline(xPositions);
         splineY = new CatmullRomSpline(yPositions);
         splineZ = new CatmullRomSpline(zPositions);
         
         float activeFragmentNum = (float)fragments.Count;
         float vy = Input.GetAxisRaw("Vertical") * 20f * Time.deltaTime;
         activeFragmentNum = Mathf.Clamp(activeFragmentNum + vy, 0, fragments.Count);
         
         for (int i = 0; i < fragments.Count; i++) {
             if (i <= fragments.Count - activeFragmentNum) {
                 fragments[i].rigidbody.position = transform.position;
                 fragments[i].rigidbody.isKinematic = true;
             } else {
                 fragments[i].rigidbody.isKinematic = false;
             }
         }
     }
     
     void LateUpdate()
     {
         LineRenderer renderer = GetComponent<LineRenderer>();
         
         for (int i = 0; i < fragments.Count; i++) {
             Vector3 position = fragments[i].transform.position;
             xPositions[i] = position.x;
             yPositions[i] = position.y;
             zPositions[i] = position.z;
         }
         
         for (int i = 0; i < (fragments.Count - 1) * splineFactor + 1; i++) {
             renderer.SetPosition(i, new Vector3(
                 splineX.GetValue(i / (float) splineFactor), 
                 splineY.GetValue(i / (float) splineFactor), 
                 splineZ.GetValue(i / (float) splineFactor)));
         }
     }
 }

Answer 1

You have error, because your logic in loop "for" is not correct. You write:

  for (int i = 0; i < (int)gameObject.transform.position.y; i++) {
   if(fragments.Count <= (int)gameObject.transform.position.y){
    fragments.Add(null);
     fragments[i] = ...

For, example, List of fragments is not empty (for example, have 5 elements). Then in condition "if" (for i == 0) you add null object. Last object have index 5, but you work with index 0. I think, you must modify last element of List. Try this:

  void Update() {
   Vector3 position = transform.position;
      
   for (int i = 0; i < (int)gameObject.transform.position.y; i++) {
    if(fragments.Count <= (int)gameObject.transform.position.y){
     fragments.Add(null);
     //Use not "i", but last index
     fragments[fragments.Count-1] = (GameObject) Instantiate(fragmentPrefab, position, Quaternion.identity);
     fragments[fragments.Count-1].transform.parent = transform;
     
     SpringJoint joint = fragments[fragments.Count-1].GetComponent<SpringJoint>();
     if (fragments.Count-1 > 0) {
      //Connect to prelast element
      joint.connectedBody = fragments[fragments.Count - 2].rigidbody;
     }
          
     position += interval;
    }
   }

   //Not use names matches with method, change "renderer" on "myrenderer"
   LineRenderer myrenderer = GetComponent<LineRenderer>();
   //Check counts:
   if(fragments.Count > 0) {
    myrenderer.SetVertexCount((fragments.Count - 1) * splineFactor + 1);

    //Not correct index, for example list have 7 elements (Count), but last index is 6
    xPositions = new float[fragments.Count - 1];
    yPositions = new float[fragments.Count - 1];
    zPositions = new float[fragments.Count - 1];
      
    splineX = new CatmullRomSpline(xPositions);
    splineY = new CatmullRomSpline(yPositions);
    splineZ = new CatmullRomSpline(zPositions);
      
    float activeFragmentNum = (float)fragments.Count;
    float vy = Input.GetAxisRaw("Vertical") * 20f * Time.deltaTime;
    activeFragmentNum = Mathf.Clamp(activeFragmentNum + vy, 0, fragments.Count);
      
    for (int i = 0; i < fragments.Count; i++) {
     if (i <= fragments.Count - activeFragmentNum) {
      fragments[i].rigidbody.position = transform.position;
      fragments[i].rigidbody.isKinematic = true;
     } else {
      fragments[i].rigidbody.isKinematic = false;
     }
    }
   }
  }

In LateUpdate() changing name LineRenderer too. I hope that it will help you.

Answer 2

Answer by Tamir1989 · Dec 08, 2014 at 08:19 AM

you set some parameters as public,(fragmentPrefab...) go to the inspector for that script, check if you have assigned the public parameters.

Tamir.

Add comment · Share

C# Need Help Finding Where Null Reference Exception Is

2 Replies

Your answer

Follow this Question

Related Questions