Unity Singleton

Singleton.cs

using UnityEngine;

public class Singleton<T> : MonoBehaviour where T : MonoBehaviour {
    // Check to see if we're about to be destroyed.
    private static bool _ShuttingDown = false;
    private static object _Lock = new object();
    private static T _Instance;

    /// <summary>
    /// Access singleton instance through this propriety.
    /// </summary>
    public static T Instance {
        get {
            if (_ShuttingDown) {
                Debug.LogWarning("[Singleton] Instance " + typeof(T) + " already destroyed. Returning null.");
                return null;
            }

            lock (_Lock) {
                if (_Instance == null) {
                    // Search for existing instance.
                    _Instance = (T) FindObjectOfType(typeof(T));

                    // Create new instance if one doesn't already exist.
                    if (_Instance == null) {
                        // Need to create a new GameObject to attach the singleton to.
                        var singletonObject = new GameObject();
                        _Instance = singletonObject.AddComponent<T>();
                        singletonObject.name = typeof(T).ToString() + " (Singleton)";

                        // Make instance persistent.
                        DontDestroyOnLoad(singletonObject);
                    }
                }
                
                return _Instance;
            }
        }
    }

    private void OnApplicationQuit() {
        _ShuttingDown = true;
    }
    
    private void OnDestroy() {
        _ShuttingDown = true;
    }
}