using UnityEngine; /// /// 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. /// public class Singleton : 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(); 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; /// /// 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. /// public void OnDestroy() { applicationIsQuitting = true; } }