Getting a script to run without attaching it to a GameObject

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I was wondering if there was a way to run a Manager / Singleton class when my game starts without attaching it to any gameObject. I need this class to hold references to my current camera and other such objects which I'd like to access from a variety of different scenarios.

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Answer by duck · Apr 30, 2010 at 04:42 PM

You need at least one script attached to a gameobject somwhere in your scene.

However you can use that script's Start() function as a hook from which to instantiate any number of your own classes which themselves aren't attached to a GameObject.

If you're going to create new instances like this, make sure that they don't inherit from MonoBehaviour, since the way that MonoBehaviour works makes some assumptions that it is attached to a GameObject.

So the rule for creating instances of scripts at runtime are:

For MonoBehaviours, always use:
gameObject.AddComponent(MyScript)
For non-MonoBehaviours, always use:
new MyScript();

In summary, you can have scripts running which aren't attached to GameObjects, but you can't get scripts running in the first place without at least one attached to a GameObject, to "kick things off".

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Disaster · Apr 30, 2010 at 04:46 PM 0

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So, in theory, I could just add a empty gameObject and attach my script to that?

yosh · Apr 30, 2010 at 10:35 PM 1

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Yeah, thats right. Im creating always a "Controller"-script and a attach that to an empty gameobject. Theres my whole functionality for key presses, loading scenes, objects etc. Here you can access other gameobjects/components, too..

Answer 2

Answer by JacobK · Sep 27, 2017 at 01:25 PM

This is possible since Unity 5 or so, using [RuntimeInitializeOnLoadMethod]

See: https://docs.unity3d.com/ScriptReference/RuntimeInitializeOnLoadMethodAttribute.html

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Harinezumi · Jun 18, 2018 at 03:44 PM 1

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I'm pretty experienced with Unity, yet this is the first time I've heard of this (see$$anonymous$$gly) extremely useful attribute! If this works as expected, it is amazing!

Answer 3

Answer by yeahdixon · May 21, 2014 at 10:07 PM

IN addition you can have a singleton class that is not a monobehavior, that has links to game object in your scene. You can Call : AppState.Instance().goGame=this.gameObject;

and can be called from within empty game object script.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class AppState  {
 
     public static AppState _instance = null;
 
 
     //holder for reference
 ;
     public GameObject goGame;
 
 
     public AppState() {
 
         Debug.Log("constructor ");
 
     
 
     }
 
 
 
     /* singleton */
     public static AppState Instance() { 
         
         if (_instance==null)
         {
             _instance=new AppState() ;
 
         }
         return _instance;
     }
 
 
 }

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Answer 4

Answer by UnitedVector · Aug 26, 2018 at 03:21 AM

Make your class extend UnityEngine.ScriptableObject, then use the ScriptableObject.Awake() function to do what you want

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LukeNukem44 · Jan 30, 2019 at 03:13 PM 0

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Just been testing that. -- It's doesn't work on it's own if it's just a script in your assets.

Getting a script to run without attaching it to a GameObject

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