Null Reference exception help

Questions & Answers
1

Would someone please help me find this Null Reference Exception?

NullReferenceException: Object reference not set to an instance of an object
RespawnDieTrigger.OnTriggerEnter (UnityEngine.Collider hit) (at Assets/Troys Scripts/RespawnDieTrigger.js:17)

RespawnDieTrigger is the trigger script which is attached to the main game object(named Sphere) which is the following script. Below this script is my Respawn script which is attached to the first person controller (named FPS)

tum1-2 is the static trigger object(its a wall)

When the sphere hits the wall(tum1-2) the First Person Controller and all of its children(main camera and sphere) respawn perfectly. In my Hierarchy each time the sphere hits the wall(tum1-2) I see the FPS, FPS(Clone) FPS(Clone)(Clone)etc… The (Clone) just adds on to the end. So what I see in the Hierarchy after five collisions is FPS(Clone)(Clone)Clone)(Clone)(Clone).Just one FirstPerson Controller with five strings of (Clone) after it. Any Ideas why I’m getting this Null Reference Exception?

function OnTriggerEnter(hit:Collider){
        if (hit.name == "tum1-2"){
        // if player hit the wall...
        Destroy(gameObject.Find("Main Camera"));
        Destroy(gameObject);
        Destroy(gameObject.FindWithTag("GameController"));
	
 	        // it suicides
            // get the object tagged "Respawn"
        var objRespawn = GameObject.FindWithTag("Respawn");
           // get the script RespawnScript.js
        var script: RespawnScript = objRespawn.GetComponent(RespawnScript);
        script.RespawnPlayer(); // respawn a new player

         }
       }
`

`

       var playerPrefab: GameObject; // drag the player prefab here

       function RespawnPlayer(){  

       Instantiate(playerPrefab, transform.position, transform.rotation);

}
3

function OnTriggerEnter(hit : Collider) {
if (hit.name == “tum1-2”) {
// This will cause null reference exception if you
// don’t create a new “Main Camera” object somewhere
Destroy(GameObject.Find(“Main Camera”));

        // This will cause null reference exception if you 
        //don't create a new object with "GameController" tag somewhere
        Destroy(GameObject.FindWithTag("GameController"));

        Destroy(gameObject);

        var objRespawn : GameObject = GameObject.FindWithTag("Respawn");

        // This will cause null reference exception if you 
        // have no game object with the "Respawn" tag somewhere
        var script : RespawnScript = objRespawn.GetComponent(RespawnScript);

        // This will cause null reference exception if you 
        // have no "RespawnScript" script on the object with the "Respawn" tag.
        script.RespawnPlayer();
    }
}

Since you’re getting names like “FPS(Clone)(Clone)Clone)(Clone)(Clone)”, I start to think that your player prefab isn’t actually a prefab, but an object in your scene. The idea is that you should create a prefab in your project and link the prefab to playerPrefab, not the actual player placed in the scene.

var playerPrefab : GameObject;
function RespawnPlayer() {  
    // This will cause null reference exception if you 
    // a) Forgot to set playerPrefab to a valid reference or,
    // b) Have destroyed playerPrefab, like in the case if you 
    //    linked to a scene object or,
    // c) Set it to null elsewhere in your code.
    Instantiate(playerPrefab, transform.position, transform.rotation);
}
2

There are several places where you can have a null reference :
if hit is null => “if(hit.name == “tum1-2”)”

if “Respawn” is not found, objRespawn will be null and then “objRespawn.GetComponent” will throw an error

if “RespawnScript” is not found => script.RespawnPlayer will throw an error

And if I remember well, GameObject.Destroy does not accept null as argument, so if you use a “Find” method that return null, it could throw a null reference.

Hope it helps !