Singleton and DontDestroyOnLoad question

Questions & Answers
1

Hi, I’m using a singleton design to keep the player profile persistent between scenes. I’m having a problem when I return to the main menu from a level.

Lets call my main menu scene A and a level in the game scene B.

in scene A I have about 30 or 40 different variables for different gameobjects, text components, image components etc. When I load scene B, I have some scripts which will access the static singleton and read data from it, the singleton persists through to scene B as expected however when I return to scene A all of the references to the variables in that scene are gone. I was expecting that scene A would load again and my menu would still have all of the references.

Here’s the code I’m using for the singleton…

public class GameController : MonoBehaviour {

	public static GameController Controller;

void Awake () {
        
		if (Controller == null) {

			DontDestroyOnLoad (gameObject);
			Controller = this;
		} else if (Controller != this) {
			Destroy (gameObject);
		}

	}

}

I’ve been reading about DontDestroyOnLoad but I’m having a bit of trouble wrapping my head around how to get over this one. A possible solution I’ve been thinking might be to not destroy the object when I go from scene A → B … but then have some sort of flag I can set up to destroy it when moving back to scene A (B → A). Does anybody have any thoughts or ideas on how I might implement such a solution? I welcome any other ideas.

Another thing to note is that I don’t actually need any of the data in the singleton object by the time I make it back to scene A (the main menu). By that time I’ve saved the gamer profile and if I could completely reload the scene , destroy the singleton and create a new instance when scene A loads, then I think that’d work perfectly. The logic inside the awake function is what I could really use help with.

Thanks everybody,
-Andrew

UPDATE :

I haven’t found a clean elegant solution to this, but I figure the solution would be to use another method in the first place so for now I’ve found a way around… What I initially wanted was to put some logic in the awake function to handle destroying the singleton when I returned to the main menu. So what I did was add a removeInstance() function to the gamecontroller class and then from my Racemanager script(the script which is linked to the button click to go back to the main menu, I simply call the Gamecontroller.controller.RemoveInstance() function and it runs Destroy(gameobject). So when I return to the main menu and there is no active gamecontroller object it just creates a new one… Seems to work…

2

When you call DontDestroyOnLoad, the object and all it’s children will persist through scenes.
It does not however ensure that the objects that it refers to are kept; those will be destroyed.

When you have such an object, you need to make sure that it does not refer to stuff that is not contained within the object itself. If that is not an option, instead of keeping references to gameobjects, just keep the values themselves. For example, instead of keeping a reference to your volume slider, just have the object write the value of the slider, and then read it back.