c# singleton

using UnityEngine;

/// <summary>

/// Be aware this will not prevent a non singleton constructor

/// such as `T myT = new T();`

/// To prevent that, add `protected T () {}` to your singleton class.

///

/// As a note, this is made as MonoBehaviour because we need Coroutines.

/// </summary>

public class Singleton<T> : MonoBehaviour where T : MonoBehaviour

{

private static T _instance;

private static object _lock = new object();

public static T Instance

{

get

{

if (applicationIsQuitting) {

Debug.LogWarning("[Singleton] Instance '"+ typeof(T) +

"' already destroyed on application quit." +

" Won't create again - returning null.");

return null;

}

lock(_lock)

{

if (_instance == null)

{

_instance = (T) FindObjectOfType(typeof(T));

if ( FindObjectsOfType(typeof(T)).Length > 1 )

{

Debug.LogError("[Singleton] Something went really wrong " +

" - there should never be more than 1 singleton!" +

" Reopenning the scene might fix it.");

return _instance;

}

if (_instance == null)

{

GameObject singleton = new GameObject();

_instance = singleton.AddComponent<T>();

singleton.name = "(singleton) "+ typeof(T).ToString();

DontDestroyOnLoad(singleton);

Debug.Log("[Singleton] An instance of " + typeof(T) +

" is needed in the scene, so '" + singleton +

"' was created with DontDestroyOnLoad.");

} else {

Debug.Log("[Singleton] Using instance already created: " +

_instance.gameObject.name);

}

}

return _instance;

}

}

}

private static bool applicationIsQuitting = false;

/// <summary>

/// When Unity quits, it destroys objects in a random order.

/// In principle, a Singleton is only destroyed when application quits.

/// If any script calls Instance after it have been destroyed,

/// it will create a buggy ghost object that will stay on the Editor scene

/// even after stopping playing the Application. Really bad!

/// So, this was made to be sure we're not creating that buggy ghost object.

/// </summary>

public void OnDestroy () {

applicationIsQuitting = true;

}

}