SingletonViaPrefab.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// by @kurtdekker - to make a Unity singleton that has some
// prefab-stored, data associated with it, eg a music manager
//
// To use: access with SingletonViaPrefab.Instance
//
// To set up:
//	- Copy this file (duplicate it)
//	- rename class SingletonViaPrefab to your own classname
//	- rename CS file too
//	- create the prefab asset associated with this singleton
//		NOTE: read docs on Resources.Load() for where it must exist!!
//
// DO NOT DRAG THE PREFAB INTO A SCENE! THIS CODE AUTO-INSTANTIATES IT!
//
// I do not recommend subclassing unless you really know what you're doing.

public class SingletonViaPrefab : MonoBehaviour
{
	// This is really the only blurb of code you need to implement a Unity singleton
	private static SingletonViaPrefab _Instance;
	public static SingletonViaPrefab Instance
	{
		get
		{
			if (!_Instance)
			{
				// NOTE: read docs to see directory requirements for Resources.Load!
				var prefab = Resources.Load<GameObject>("PathToYourSingletonViaPrefab");
				// create the prefab in your scene
				var inScene = Instantiate<GameObject>(prefab);
				// try find the instance inside the prefab
				_Instance = inScene.GetComponentInChildren<SingletonViaPrefab>();
				// guess there isn't one, add one
				if (!_Instance) _Instance = inScene.AddComponent<SingletonViaPrefab>();
				// mark root as DontDestroyOnLoad();
				DontDestroyOnLoad(_Instance.transform.root.gameObject);
			}
			return _Instance;
		}
	}
	
	// NOTE: alternatively to a prefab, you could use a ScriptableObject derived asset,
	// make a reference to it here, and populated that reference at the Resources.Load
	// line above.

	// implement your Awake, Start, Update, or other methods here... (optional)
}

This method of never having prefab managers in scenes seems powerful. Thanks!

Thx, it really inspired me. But i got some problems.
In this case how the Awake or Start method works.
I think the Awake of this instance will be lazy. It will be triggered when Instance is referenced in other scripts. So that we can not add something about global initialization.
How to resolve it?

Thx, it really inspired me. But i got some problems. In this case how the Awake or Start method works. I think the Awake of this instance will be lazy. It will be triggered when Instance is referenced in other scripts. So that we can not add something about global initialization. How to resolve it?

This is how all singletons work, they are initialized on first use. If you want to make it initialize early, then you can do that by calling new() on the _Instance where it's declared rather than in the getter.

If you want to make it initialize early, then you can do that by calling new() on the _Instance where it's declared rather than in the getter.

NOTE: This is for use in Unity3D. In Unity3D you cannot call new() to Instantiate a prefab.

In this case how the Awake or Start method works.

The same way it always does: https://docs.unity3d.com/6000.1/Documentation/Manual/execution-order.html

I think the Awake of this instance will be lazy. It will be triggered when Instance is referenced in other scripts.

Correct.

How to resolve it?

Resolve what?

Hi @kurtdekker thank you for this and all of your guidance across these forums!

I am relatively new to this process and was referred to this page for help creating a self-instantiating singleton (in this case, a Scene History Manager object) without needing to use "DestroyOnLoad" or having a redundant instance in every scene -- where i'm getting tripped up is the "To use: access with SingletonViaPrefab.Instance" bit -- if I'm using the code correctly, should this object instantiate in any scene in my project simply by existing in the Resources folder, or do I need to summon it with a script attached to an object that's in the scene?

Thank you in advance!