Is it possible to perform a TRUE null-check?

Question

I'm aware of how ==null behaves in classes derived from UnityEngine.Object - no need to explain that. However it really stands in my way, because it seems I'm unable to perform true null-check. Like: I have no way to differentiate destroyed object from real null. Is there any way to find out, if a reference is really a null, not a destroyed object? Or do I have to do some workarounds?

Answer 1

Best Answer

Answer by Sushi271 · Aug 03, 2016 at 06:40 AM

Found it!

Apparently there is much, much simpler way to compare with true null. One property of == operator saved the day: it is not polymorphic. It means, that though every descendant of UnityEngine.Object gets this nasty surprise as a gift, there is one ancestor of UnityEngine.Object, which remembers good old ways: System.Object.

In other words:

 bool a = destroyedObject == null;
 bool b = (System.Object)destroyedObject == null;
 bool c = (object)destroyedObject == null;

Variable a will be true, whereas b and c will be false, since destroyedObject is not a null reference. In fact c is just a simpler way to write b.

Unsurprisingly, calling Equals method even when object is cast to System.Object does not work - since Equals is polymorphic.

Actually I wrote myself an extension method just so I wouldn't need to use cast all the time:

 public static bool IsTrueNull(this UnityEngine.Object obj)
 {
     return (object)obj == null;
 }

Of course you can call extension method even on null references (so it works), since it isn't a true member, just a syntactic sugar.

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Bunny83 · Aug 03, 2016 at 09:55 AM 1

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Uhm, isn't that pretty much exactly what i wrote as an answer 10 hours ago? You said

I'm aware of how ==null behaves in classes derived from UnityEngine.Object - no need to explain that

But in your own answer you seems to be suprised and you actually explain it.

Sushi271 Bunny83 · Aug 03, 2016 at 11:27 AM 0

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Somehow this answer says it's been posted 4 hours ago, but in fact I posted it merely 2 hours after posting a question... So your answer 10 hours ago appeared for me much later than my own answer.

And yes, I was aware, that ==null with Unity objects returns true with both nulls and destroyed objects. I was also aware that == operator in C# isn't polymorphic. But it just took me a while to connect the dots, that I can use == operator from System.Object, by casting on it. And I always explain solution to my own problems on any StackExchange, as a habit, so other people with the same problem can get the solution. It's a nice gesture, compared to answers like "Never $$anonymous$$d, I found the solution."

Bunny83 Sushi271 · Aug 03, 2016 at 11:49 AM 1

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Yes, you're right ^^. I usually check the revision history

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Sushi271 Bunny83 · Aug 03, 2016 at 03:05 PM 0

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As a matter of fact, I'm kinda amazed how similar our answers are, even though none of us have seen the other one before writing his own... :) Even the idea of an extension method.

Zendist · Aug 03, 2016 at 11:48 AM 0

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I must agree with Bunny83 here. Why did you make your own answer as a copy of his/hers? That's in pretty poor taste.

Sushi271 Zendist · Aug 03, 2016 at 02:10 PM 2

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Because I didn't. $$anonymous$$y answer was posted long before Bunny83's, but it was awaiting moderation, that's why it arrived later. Check revision history.

Zendist Sushi271 · Aug 28, 2016 at 02:35 PM 0

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I noticed :) - my bad.

Answer 2

Answer by Gread72 · Aug 03, 2016 at 01:11 PM

Here is another way to check for null : Object.ReferenceEquals

 public GameObject myGameObj;    
 if( Object.ReferenceEquals( myGameObj, null ) )
 {
     Debug.Log("myGameObj is null");
 }

It is slightly faster depending on the implementation.

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OndrejP · Oct 24, 2018 at 07:42 AM 1

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This is best answer, it makes intent clear.

FlightOfOne · Jan 17, 2019 at 06:54 PM 0

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This seems to work IF the class in question is either set as private or not serialized in the inspector. Looks like it gets constructed as soon as it is visible in the inspector.

  Debug.Log("Is Null?:" + lastDetected==null); False
  Debug.Log("CAST Is Null?:" + (object)lastDetected == null); False
  Debug.Log("REF Is Null?:" + object.ReferenceEquals(lastDetected,null)); True if set as private

I guess I will have to check for null and if initialized..

Answer 3

Answer by Bunny83 · Aug 02, 2016 at 11:28 PM

Yes you can test if a reference is really null by simply casting it to "object".

Example:

 Transform someObjectReference;
 
 if (someObjectReference == null)
 {
     if ((object)someObjectReference == null)
     {
         // Really null
     }
     else
     {
         // Unity fake null
     }
 }

I think an extension method like this should work as well:

 public static class UnityObjectExtension
 {
     public static bool IsRealNull(this UnityEngine.Object aObj)
     {
         return (object)aObj == null;
     }
 }

With that you should be able to do this:

 if (someObjectReference.IsRealNull())
 {
 }

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Sushi271 · Aug 03, 2016 at 11:44 AM 0

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Thanks, that's pretty much the same that I came up with. However, what I said in other comment, because my own answer was awaiting moderation, and your didn't, it appeared after your, even though I posted it long before. +1 Anyway.

Answer 4

Answer by mrpmorris · Aug 03, 2016 at 11:01 AM

Just use the static Object.ReferenceEquals() method

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OndrejP · Oct 24, 2018 at 07:42 AM 1

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This is best answer, it makes intent clear.

Answer 5

Answer by initram · Aug 03, 2016 at 01:44 AM

you can Either cast to System.Object, and then compare with == null, or you can use System.Object.ReferenceEquals(mythingie, null);

The cast to object is marginally faster.

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Is it possible to perform a TRUE null-check?

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