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. Unity - Scripting API: MonoBehaviour.Start()
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.
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.
That is pretty lame documentation. On the Monobehavior description they say this:
Note: The checkbox for disabling a MonoBehavior (on the editor) will only prevent Start(), Awake(), Update(), FixedUpdate(), and OnGUI() from executing. If none of these functions are present, the checkbox is not displayed. Unity - Scripting API: MonoBehaviour
I just tried it out with Awake, Start, and OnLevelWasLoaded
With an enabled object I got both Start and Awake, with a disabled object, neither, and neither called OnLevelWasLoaded.
In answer to the Init question: if you really wanted to, I’m sure you could call a custom Init function using OnLevelWasLoaded and an object with the DontDestroyOnLoad attribute. If you’re more specifically interested in an OnApplicationStart event you could have a scene specifically for initialization scripts.
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();
Since the constructor solution kept throwing Errors i found another way to do it (in my case it worked):
I encapsulated my GameObject with another empty GameObject which has a script attached to it doing the initialization stuff. The top GameObject is enabled (and therefore executes Start() and Awake()) while the child is disabled and gets enabled when needed.
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 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();
}
}
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");
}
}
As an alternative, you can start your object as enabled and write a quick script that automatically disables your component as soon as it starts. That way you can have the code in your Awake function as you expect, and the object will immediately return to its disabled state. Obviously this might not be helpful in every scenario but it’s another potential option.
I join the others saying that Awake (as OnDestroy) not called if object was inactive all the time.
I made a workaround in my very specific case, which I want to share. My case is the need to check some logic on start scene - it’s only for developers, so checking in editor only is enough. This is how I resolved that:
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’
