Null freezing issue (C#)

Unity Engine
1

Hi,

I was working on a small piece of my game when Unity started to freeze. I just spent 4 hours breaking my code in to ever smaller pieces, trying to find the cause, until I was down to a single Debug.Log() line:

Debug.Log(xform.name);

It finally occurred to me that when ‘xform’ is null, it freezes Unity… not a crash, a total complete freeze.

This makes me angry, and at the same time I’m just happy it’s over and I can get back to work.

Please tell me this is gone in Unity3!!?

2

What would you expect it to output? You didn’t pass it an argument if the value doesn’t exist.

3

I have a function that returns a transform or null.

If I Debug.Log(xform.name), and xform is null, I would expect an error. Something like “Null object does not have the property ‘name’.”…or whatever is standard wording for C#.

I do not expect it to freeze Unity so I have to kill the process, and repeat 50 or 60 times until I find the cause.

4

What code do you have wrapping that Debug.Log call? If it throws an unhandled exception, it may be your code causing an infinite loop or something.

So far I have yet to have an issue with Unity freezing from unhandled exceptions.

5

Nothing wrapping it. I’ll try and post a repro asap.

6

OK, this causes a freeze every time I run it:

        Debug.Log("Start Test");
        Transform xform = transform;
        Debug.Log(xform.name);
        xform = null;
        Debug.Log(xform);       // OK to here.
        Debug.Log(xform.name);  // Freeze!

Take out the last Debug.Log line and it works as expected.

  • Rafe
7

I created an empty Unity project (version 2.6.1), Added an empty game object, created a new C# script, attached the script to the game object and pasted your code into its update method.

Every frame I get the NullReferenceException (as expected), but it doesn’t cause a hang. It doesn’t hang in the webplayer either.

Try downloading the project I created here:
http://genexissystems.com/NullReferenceCrash.zip

Let me know if that hangs for you too.

8

I’ll download your project asap (on my iPhone ATM).

I forgot to post my details. I’m on windows 7, and I think I have the latest unity but I’ll have to check. What setup were you running when you made the test project?

Cheers

9

I’ve seen null references freeze and crash Unity more times than I care to count. I wish I had a good workaround to suggest, but I don’t. I guess we just have to be more diligent about checking for null until debugging support is released.

.

10

Windows XP, 32bit.