NullReferenceException problem in Unity when object is not null

Question

I am trying to troubleshoot the following piece of code which causes a NullReferenceException. Essentially when an object is created, I'm trying to have it register with my game manager class. This is the component for my object:

void Start()
{
    Debug.Log("Registering");
    if (gameObject != null)
    {
        GameMngr.Instance.RegisterAttraction(gameObject);
    }
    else
    {
        Debug.Log("Gameobject null");
    }
}

In my game manager I have the following:

public void RegisterAttraction(GameObject newAttraction)
{
    if (newAttraction != null)
    {
        Debug.Log("Attempting to register gameObject");
        attractionLastID++;
        sceneAttractions.Add(attractionLastID, newAttraction);
        Debug.Log("Registered");
    }
    else
    {
        Debug.Log("unable to register: null provided");
    }
}

My console output is as following:

Registering
Attempting to register gameObject
NullRefereceException

The fact that my code displays the attempting to register gameObject lines leads me to believe that my newAttraction variable is not null. Why do I get the error ?

Thank for the help

print the gameobject instanceID , maybe it is not a same gameobject ?? — TimChang, Sep 27 '19 at 02:55
_"NullReferenceException problem in Unity when object is not null"_ -- the idea that you might get `NullReferenceException` when the reference is not in fact null is just nonsensical. The null value may be something other than the one you think it should be. But there is *definitely* a null value that you're trying to dereference. See proposed duplicate for complete details on how to debug the problem. — Peter Duniho, Sep 27 '19 at 02:55
`GameMngr.Instance.RegisterAttraction(gameObject);` How to sure that it is set from your script ? , mabye it is from other script and you think it is from your script. — TimChang, Sep 27 '19 at 03:00
also make sure you [**never** use `== null`/`!= null` for references of type `Object`](https://stackoverflow.com/a/58069056/7111561) in Unity! — derHugo, Sep 27 '19 at 07:06

score 2 · Accepted Answer · edited Sep 27 '19 at 04:29

Where's attractionLastId defined by chance? Is it being initialized? Since you're doing a null check inside of your Start function already, try refactoring your RegisterAttraction function to look something like:

public void RegisterAttraction(GameObject newAttraction)
    {

            Debug.Log("Attempting to register gameObject");
            attractionLastID++;
            sceneAttractions.Add(attractionLastID, newAttraction);
            Debug.Log("Registered");
    }

I highly recommend setting a breakpoint on the beginning curly of RegisterAttraction. Take it step by step and hover over each variable to see which one is null.

Turns out that the issue was with sceneAttractions - it wasn't initialized early enough. Thanks for suggesting the breakpoint! — user387302, Sep 27 '19 at 03:15

NullReferenceException problem in Unity when object is not null

1 Answers1