FIndObjectOfType Problem when Changing Scenes

Question

When I change scenes using:

 SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);

I keep the player and some other objects constant (because I want them to be transferred between scenes). In my scripts, I've got FindObjectOfType() etc. in the Start() function, however this doesn't seem to be fast enough sometimes, as I end up with references to old gameObjects (e.g. that are replaced by the new gameObjects coming from the other scene). I might have a dummy player in the scene so I can test it, but in the actual game, that player will get replaced by the "real" player when they change scenes.

My current workaround is to have a bool flag, then in the Update() loop after a timer of 0.01s, I do the FindObjectOfType stuff there, then turn the flag on. This means the references are all correct, but doesn't seem like a good way of handling this problem.

Some pseudocode:

 private Player myPlayer;
 private bool foundPlayer;
 private float waitTime;

 Start(){
     myPlayer = FindObjectOfType<Player>(); // Sometimes not fast enough...
     waitTime = 0.01f;
 }

 Update(){
     if (waitTime > 0){
         waitTime -= Time.deltaTime; // Count down for 0.01s
     }
     if (!foundPlayer && waitTime <= 0){ // After 0.01s, if we don't have the reference
         myPlayer = FindObjectOfType<Player>(); // Set the correct reference
         foundPlayer = true;
     }
 }

Is there a better solution to this?

Answer 1

Best Answer

Answer by Cynikal · Aug 29, 2016 at 03:41 PM

If you want to do a call when a new scene was loaded, why not use:

 void OnLevelWasLoaded()
 {
 //Blah Blah this only works when using SceneManager.Load
 }
 
 //OR
 
 void OnLevelWasLoaded(int sceneindex)
 {
 //Blah Blah this only works when using SceneManager.Load
 }

As far as the old gameobjects, i'm assuming you're using a list. You could remove the "bad" gameobjects with something along the lines of:

 MyHashSet.RemoveWhere(s => s == null);

This is helpful if a gameObject was once there...but has been unloaded (aka, switched scenes), therefore, it'd be null.

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Nephtis · Aug 29, 2016 at 03:50 PM 0

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Thanks for telling me about this function, I'm doing something similar with the removal of old gameObjects, unfortunately doing it this way still leads me to the problem of:

Load into a new scene (from another scene)
The "OnLevelWasLoaded()" function immediately gets called and starts pointing to the old gameObject (the one that gets replaced)
The gameObjects are then switched (I can't seem to change the order this happens in, the switching always seems to come last), but everything is still pointing to the old gameObjects

So what I need to do is do the switching BEFORE I set the references to things - this is why I had that 0.01s delay, just to make sure everything was loaded and switched before pointing things at it.

The way I remove old gameObjects is:

 private static bool playerExists;

 // ...

         if (!playerExists) // If a player doesn't exist in the scene
         {
             playerExists = true; // Now a player does exist
             DontDestroyOnLoad(transform.gameObject);
         }
         else // if a player does already exist in the scene
         {
             Destroy(gameObject); // Destroy it
         }

Cynikal ♦ Nephtis · Aug 29, 2016 at 03:56 PM 1

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The RemoveWhere portion was intended to remove any null gameobjects.

Regarding the OnLevelWasLoaded, you could initiate a Coroutine that has a built in .1sec delay, ultimately getting you far away from doing it in the Update.

If you have objects A, B, and C on Scene 1. Then you load into Scene 2, and now you have objects D, E, and F. Objects A, B, and C are now null.

Nephtis Cynikal ♦ · Aug 29, 2016 at 04:07 PM 0

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Ok, so I ended up doing that with a 0.01s delayed coroutine, and it does save me having to do it from within Update() every time. Having to manually delay it still kind of sucks but until I can figure out how to change the order of things happening on scene load, this works well for now.

FIndObjectOfType Problem when Changing Scenes

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