Exposed variable is null in Awake

Question

I have an exposed variable that I attach to in the Inspector. But when I run the game Unity throws a NullReferenceException in the script's Awake() function. And - yes, I am sure the variable is attached. Also, I've tried Start() instead and the same happens.

Even more weird, after Awake() (i.e. Update()) the variable is set properly and the whole script/game seems to be running fine, like there was never any error. Yet one is thrown.

Any ideas what might be the problem and how to fix it? I don't feel comfortable leaving an error in my game.

Track.cs:

 using System.Collections.Generic;
 using UnityEngine;
 
 public class Track : MonoBehaviour
 {
     public MegaShape envCrossSectionCCW;
 
     [HideInInspector]
     public MegaShape envCrossSectionCW;
 
     void Awake()
     {
         var cw = (GameObject)Instantiate(envCrossSectionCCW.gameObject);   // NullReferenceException
         cw.transform.parent = envCrossSectionCCW.transform.parent;
         cw.name = "EnvCrossSectionCW";
         envCrossSectionCW = cw.GetComponent<MegaShape>();
     }
 }

Edit: When I try to debug the code the debugger stops at the commented line and when I check the value of envCrossSectionCCW it is null. However, when I try to proceed to the next line of code in the debugger it jumps... again to the same line of code (like it resetted or sth) and this time envCrossSectionCCW isn't null anymore. From this point the debugging proceeds without a problem.

EDIT: Today I've discovered that my Awake() is called twice(!) for some reason (that debugger behaviour was just that - it went through the code twice, first time ending in an error). The GameObject with Track script is stores in Resources and instantiated like that:

  (GameObject)Instantiate(Resources.Load("TrackMountainsForest"));

I'm pretty sure I have only 1 object with this script attached in the entire scene. Any idea why Awake() gets called twice?

Answer 1

Answer by brunopava · Jun 30, 2014 at 11:46 AM

The var keyword is used on Javascript, to declare variables with C# you simply state the type of it.

 //Your code
 var cw = (GameObject)Instantiate(envCrossSectionCCW.gameObject);
 
 //My code
 GameObject cw = GameObject.Instantiate(envCrossSectionCCW.gameObject, 
                                        positionVector, 
                                        rotationVector) as GameObject;

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Denvery · Jun 30, 2014 at 11:48 AM 0

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Var in c# and in this code is absolutely legal: http://msdn.microsoft.com/ru-ru/library/bb383973.aspx

NPS · Jun 30, 2014 at 12:12 PM 1

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What Denvery said + just to be sure I've checked - specifying the type explicitly doesn't make the error go away.

hackingdandan NPS · Jan 02, 2021 at 06:09 PM 0

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yeah C# has allowed inferred variable declaration since c# 3.

Only exception is if you're just declaring the name of the variable to instantiate it later.

 GameObject myThing;
 
 myThing = GameObject.Instantiate(...);

*edited

Bunny83 hackingdandan · Jan 02, 2021 at 06:37 PM 0

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"var" is not a dynamic variable. It's not dynamic as in "it can change its type dynamically". It's just a type inferred variable declaration. Implicitly typed variables can only be declared inside methods and not inside class / type declarations.

A dynamic variable in C# would be a variable of type "object". Besides that there is the type "dynamic". However it comes with runtime overhead and generally makes code harder to read and debug-

You did realise that this question and comment is over 6 years old, right?

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Exposed variable is null in Awake

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