Question by Cirrocumulus · Feb 26, 2018 at 03:11 PM · nullreferenceexception scene-loading scene-switching

Cleaning up before LoadScene

I've been having a problem, like many people here, with a "MissingReferenceException" when using the SceneManager to do a LoadScene. I don't have any scripts using DontDestroyOnLoad, I just want to wipe everything clean and load my menu scene back. I've tripled-checked my event subscriptions pairs (in OnEnable and OnDisable) and they all look fine. The error is caused by different scripts it seems, with one being particularly touchy, a script which uses OnBecameInvisible (code below). Could it be that Unity calls "OnBecameInvisible" when doing a LoadScene? Thanks for your help.

 public class DestroyWhenOutsideViewport : MonoBehaviour {
 
     private Camera cam;
 
     private void Awake()
     {
         cam = Camera.main;
     }
 
     public void OnBecameInvisible()
     {
         Vector3 pos = cam.WorldToViewportPoint(transform.position);
         if (pos.x > 1.0 || pos.x < 0 || pos.y > 1.0 || pos.y < 0)
         {
             Destroy(gameObject);
         }
     }
 }

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NickJVaccaro · Feb 26, 2018 at 03:57 PM 0

According to the Execution Order, Awake should definitely be called before OnBecameInvisible. Have you tried tossing in a few Debug.Log() statements to get a better look at how everything is behaving? Also, which references is missing? Is it blowing up when you try to call cam.WorldToViewportPoint()?

Cirrocumulus NickJVaccaro · Feb 26, 2018 at 04:04 PM 0

Well, nothing really blows up, even in a development build I only get a $$anonymous$$issingReferenceException when going back to the menu and then everything behaves normally again. Because I was getting the error mostly from OnBecameInvisible in a script which extends my base "Entity" class, I thought I'd add the following to the base "Entity" class, which only made matters worse because now I get $$anonymous$$issingReferenceException in both places, the derived class and the base class. I don't know where I can put debug checks because Unity apparently gets rid of objects at random when unloading a scene, but there's probably something very basic here that I've missed.

 public virtual void Awake()
 {
     Scene$$anonymous$$anager.sceneUnloaded += OnSceneUnloaded;
 }
 
 private void OnSceneUnloaded(Scene arg0)
 {
     if (gameObject != null)
         Destroy(gameObject);
 }