Something like Awake that runs even if disabled?

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The documentation for Start says:

Like the Awake function, Start is called exactly once in the lifetime of the script. However, Awake is called when the script object is initialised, regardless of whether or not the script is enabled. Start may not be called on the same frame as Awake if the script is not enabled at initialisation time. http://docs.unity3d.com/ScriptReference/MonoBehaviour.Start.html

It always seemed to me like Awake would be called regardless of whether an object were enabled or not, whereas Start would be called only when the object became active. And that this would apply to app startup. But that does not appear to be the case.

http://forum.unity3d.com/threads/unityevent-disabled-objects-awake-failure.267241/

My question is whether there is anything like Awake that is called even on disabled objects when the app is started. Because that would be terribly handy. (Or am I misunderstanding Awake, maybe it does somehow run on disabled objects at startup?)

So I think I do understand the difference between Awake and Start. If you Instantiate an object then disable it, Awake will run but Start will not. So you should initialize the object itself in Awake and its connections in Start.

What I'm asking is why can't there be another callback, like Init, which runs only at app startup, for all disabled objects in the scene, if it exists. Unity could make a list of which ones to call when it builds the scene, so it doesn't have to traverse the scene hierarchy at startup. (This is basically how static initialization functions are compiled in some languages.)

At the very least I think the docs should be clearer that Awake is not called at startup if the object is not enabled, because it really seems like it would be, as the docs currently describe.

Answer 1

Answer by Schnodahipfe · Jul 24, 2017 at 12:15 PM

Another option, which I use is the following:

Have the gameobject active in the hierarchy
Do all initializations in Awake()
Then deactivate the gameobject in Awake() after the initializations

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Answer 2

Answer by brinca · Aug 18, 2018 at 04:44 AM

Having a Create() method that gets called even if the object is inactive would be awesome, but alas, not (yet) supported, so perhaps the next best thing is to make your own... ;)

The approach I use uses an interface IInitable that defines a single Init() method:

 public interface IInitable {
    void Init();
 }

On the scene manager (or any other script for that matter), I gather all the instances that implement IInitable, and call Init() on them:

 var scripts = gameObject.GetComponentsInChildren<IInitable>(true);
 
 foreach (var script in scripts)
     script.Init();

Yes this is slow (you should use this only when setting up the scene), and yes it'll not work when instantiating new objects (but then you can call Init() manually), but it gets the job done.

Final tip, if you don't have all your game objects under a single root (what I call the scene manager), you'll have to iterate each root object of each scene when looking for IInitable instances:

 var scripts = new List<IInitable>();
 var scene = SceneManager.GetActiveScene();
 
 var rootObjects = scene.GetRootGameObjects();
 
 foreach (var go in rootObjects)
     scripts.AddRange(go.GetComponentsInChildren<IInitable>(true));

 foreach (var script in scripts)
     script.Init();

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Bonfire-Boy · Aug 18, 2018 at 02:41 PM 0

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Another option, is to give the scenemanager the responsibility of deciding which objects can have this done. You could for example give it a public array of gameobjects which you populate with those objects. This would speed things up (no need to find them) and also give you a bit more flexibility (you'd still have the option of properly turning the objects on and off, by removing/adding them to the array)

brinca Bonfire-Boy · Aug 19, 2018 at 08:44 AM 0

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Linking the instances to the scene manager, either through references in the Editor or through code is the optimal way of course, but that isn't the point of the OP's original question... in cases where you either can't or don't want to link explicitly (e.g. if you want to decouple your scripts from the scene manager), then my suggestion provides a nice way to implement a callback that is always run, even if the game object is disabled.

Bonfire-Boy brinca · Aug 19, 2018 at 09:49 AM 0

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This way of doing things isn't for me, as explained above. But I recognise that some people might want to do it. So my comment to your answer wasn't intended to criticise it, just pointing out "another option", as I said.

But I'm not sure what you mean by "decouple from the scene manager". How does my tweak make anything more dependent on the scene manager than yours? All it does it change how the scenemanager gets to know about the IInitables

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the_mr_matt · Nov 05, 2018 at 06:34 PM 0

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How would I go about creating a priority system for this? Before I relied on the script execution order to ensure my scripts initialized in a specific order but calling them manually from one script breaks that. I can't put a field into the IInitiable interface for priority and I don't want to make an abstract class because I'm already inheriting from other abstract class and it would just become a mess.

brinca the_mr_matt · Nov 05, 2018 at 06:48 PM 0

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When you say you can't is it because the requirements won't allow it, or is it simply because interfaces don't support fields?

If the latter, simply use a property int Priority { get; set; }, and then sort the scripts array before calling Init().

If the former, then one way to get around that would be to use interfaces to mark the script's priority (IPriorityHigh, IPriorityNormal, IPriorityLow, etc), then check for those when finding the instances if (script is IPriorityHigh) ...and store them into different arrays, then call Init() on each array according to it's priority.

the_mr_matt the_mr_matt · Nov 05, 2018 at 06:54 PM 0

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Got it to work using a property. I can just return a constant integer in the property and then in before initializing the scripts I sort the list by the priority property using linq. Gonna be awfully slow but it works...

brinca the_mr_matt · Nov 05, 2018 at 06:56 PM 0

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No problem in being slow if it's not performance critical... ;)

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moment_um · Jun 04, 2019 at 06:17 PM 0

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I might be mistaken, but calling GetComponentsInChildren does not work on inactive gameobjects. So we run back into the same problem.

Bunny83 moment_um · Jun 04, 2019 at 06:31 PM 0

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GetComponent(s) should always work, no matter if the object is active / deactivated or if the component is enabled or not. GetComponentsInChildren has an optional parameter to specify if deactivated gameobjects should be traversed or not. As you can see in the code he provided he passed "true".

Answer 3

This might not help your scenario, but I was running into similar problems with wanting Awake to be called on deactivated GameObjects and children.

My situation was: I needed to deactivate my HUD GameObject at the very beginning of the game (because my game starts at the title screen, where the HUD should not be shown). But this caused Awake() to not be called on all the children of the HUD GameObject!

In Awake() in my HUD script (attached to the root GameObject of the HUD), I was using: gameObject.SetActive(false);

And consequently, all of the children scripts were not having their Awake()s being called at all. However, I found out that one possible way to help this is to deactivate the GameObject on Start() instead. Start() is still called early enough that, if I deactivate the object then, we won't see the HUD flash on the screen at all for a frame -- but it happens after all the Awake()s are called!

 using UnityEngine;
 
 public class HUD : MonoBehaviour {
     public void Start() {
         gameObject.SetActive(false);
     }
 }

I hope this helps! :)

Answer 4

Answer by Lumpazy · May 04, 2019 at 04:43 PM

Oh yeah Earth to unity : Anyone there who would think of mentioning, that a disabled scripts Awake function is executed in the actual documentation of Awake ?

Oh no. It makes Soooo much mooore seeense to mention it in the documentation for 'Start'

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Answer 5

Answer by vfxjex · Sep 30, 2020 at 10:11 PM

Just in case someone bumps into this problem 1st - I made a gameobject called Initializer with this simple script attached, using UnityEngine;

 public class Initializer : MonoBehaviour
 {
     public delegate void Initialize();
     public static Initialize initialize;
 
     void Awake()
     {
         initialize();
     }
 }

2nd - in your script that you want to initialize, add a Constructor and Initialize Method like this,

       using UnityEngine;
         public class MyScript: MonoBehaviour
         {
         bool isInitialized;
             MyScript()
             {
                 Initializer.initialize += Initialize;
             }
         
             void Initialize()
             {
                 if(this == null)
                 {
                     Initializer.initialize -= Initialize;
                     return; 
                 }
                 if (isInitialized)
                 {
                    Initializer.initialize -= Initialize;
                    return;
                 }
                 isInitialized = true;
                 Debug.Log("I WAS INITILIZE");
             }
         }

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Bunny83 · Sep 30, 2020 at 10:47 PM 0

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While this does solve any issues with the loading thread (since you delegate the initialization to another Awake method) this comes with several other issues. First of all in the Unity editor the objects might be created / recreated more often than you may think. So this could still be an issue. Likewise you introduce a memory leak because since you register an instance method to that delegate, that delegate will keep those objects alive forever. This could result in all sorts of hidden issues. At least clear the initialize delegate after you called it.

Similarly if this script ends up on a prefab, since your Initializer awake method is only called once any object instantiation after the Awake method has been called will still register the delegate but it will never be called or cleaned up.

Xtro · Sep 30, 2020 at 11:00 PM 0

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Doesn't work when the gameobject is disabled.

Something like Awake that runs even if disabled?

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