NullReferenceException problems

Questions & Answers
1

So I am working on a gravity simulation in 3D, and I have been getting some really strange NullReferenceExceptions. The errors for now are occurring on line 107, it reads:

tSeparationVector = objects[j].transform.position - objects*.transform.position;*

Here is the rest of the code:



var objectList = new Array();

private var objects : GameObject[] = new GameObject[10];

var masses = new Array();


var locX:int; var locY:int;

var worldSizeX:int = 50;

var worldSizeY:int = 50;

var prefab:Transform;

var prefab1:Transform;

var index:int = 0;

var index1:int = 0;

var sunExists:System.Boolean = false;

var bodyScale;

var sun : Transform;


//physics variables;

private var _COM : Vector3 = Vector3.zero;

private var _GravConstant : float = 6.673 * Mathf.Pow(10.0, -11.0); // Units: m3 kg-1 s-2

private var _SimTime : float = 0.0; // D (Days)

private var _Mass : float = 0.0;


private var _DistanceConversion : float = 6.68458712 * Mathf.Pow(10.0, -12.0); // m → AU (Astronomical Units)

private var _MassConversion : float = 1.67403241 * Mathf.Pow(10.0, -25.0); // kg → E (Earth masses)

private var _TimeConversion : float = 1.15740741 * Mathf.Pow(10.0, -5.0); // s → D (Days)

var nextPlanet : Transform;


function Update(){

  • if(index <= 9){*

  •  //generates a random position on the horizontal plane that is inside the world size values.*

  •  var position: Vector3 = Vector3(Random.Range(-worldSizeY, worldSizeX), 0, Random.Range(-worldSizeY, worldSizeY));*

  •  objectList.push(position);*

  •  index1++;*

  •  }*

  • //if there is a sun, dont make another. If not, create a sun.*

  • if(sunExists == false){*

  •   sun = GameObject.Instantiate(prefab1, new Vector3(0,0,0), Quaternion.identity);*

  •   objects[0] = GameObject.sun;*

  •   masses[0] = 100;*

  •   sunExists = true;*

  • }*

  • //makes nine bodies to orbit the sun.*

  • if(index <= 9){*

  • //creates the scale of the next body*

  • bodyScale = Random.Range(2,12);*

  • //sets the body’s mass*
    _ masses[index+1] = 5.9742* Mathf.Pow(10, 24);_

  • //sets the scale of the next body*

  • prefab.localScale = Vector3(bodyScale, bodyScale, bodyScale);*

  • //instantiates a new body and adds to the GameObject array*

  • nextPlanet = GameObject.Instantiate(prefab,objectList[index],Quaternion.identity);*

  • objects[index] = GameObject.nextPlanet;*

  • //adds one to the index*

  • index++;*

  • }*

  • // Convert the gravitational constant’s units*
    _GravConstant *= Mathf.Pow(_DistanceConversion, 3.0);

  • _GravConstant /= _MassConversion;*

  • _GravConstant /= Mathf.Pow(_TimeConversion, 2.0);*

  • applyForces();*
    }
    function applyForces(){

  • // Initialize the kinetic and potential energies*

  • var tKineticEnergy : float = 0.0;*

  • var tPotentialEnergy : float = 0.0;*

  • // Initialize the NxN matrix to store the gravitational forces between each body-pair*

  • var tForcesMatrix : Array = new Array[objects.length];*

  • // Initialize a matrix to store the total forces to apply on each body*

  • var tTotalForcesArray : Vector3 = new Vector3[objects.length];*

  • // Walk each body in the system*

  • for (var i : int = 0; i < objects.length-1 ; i++) {*

  •   // Initialize this body's gravitational forces array and total force value*

  •   var tForcesArray : Vector3[] = new Vector3[objects.length];*

  •   var tTotalForce : Vector3 = Vector3.zero;*

  •   //var tSeperationVector : Vector3 = Vector3.zero;*

  •   var tForceValue : float;*

  •   // Walk each body-pair in the system*

  •   for (var j : int = 0; j < objects.length-1; j++) {*

  •   	var tSeparationVector : Vector3 = new Vector3(0,0,0);*

  •   	// Check the body-pair indices*

  •   	if (i != j) {*

  •   		// Calculate the gravitational force between these two bodies*

_ tSeparationVector = objects[j].transform.position - objects*.transform.position;_
tForceValue = (_GravConstant * masses _ masses[j]) / tSeparationVector.sqrMagnitude;
tForcesArray[j] = tSeparationVector.normalized * tForceValue;_

* // Update the potential energy if necessary*
_ if (i < j) { tPotentialEnergy -= (tForceValue * tSeparationVector.magnitude); }_

* } else {*

* // Use a zero vector, no self gravitation*
* tForcesArray[j] = Vector3.zero;*

* }*

* // Increment the total force to apply*
* tTotalForce += tForcesArray[j];*
* }*
* // Add this body’s forces array to the matrix and total force to the array*
_ tForcesMatrix = tForcesArray;
tTotalForcesArray = tTotalForce;
* }*_

* // Finalize the center of mass vector*
_COM = (1.0 / _Mass) * _COM;

* // Apply the total force to each body in the system*
* for (var k : int = 0; k < objects.length-1; k++)*
* {*
* objects[k].rigidbody.AddForce(tTotalForcesArray[k]);*
* }*
}


Sorry for the wall of code, but I think that in order to find the problem, it is necessary to see everything that I am doing.
Thanks so much for your help.

2

The problem seems to be coming from casting the transform (from instantiate) to a gameobject.
Try changing

private var objects : GameObject[] = new GameObject[10]; -> to -> private var objects : Transform[] = new Transform[10];

Im not used to javascript so I dont know what to do if you want to keep it as a GameObject. The casting doesn’t give a problem in C#.