PrinceOfGlory/Assets/Scripts/XRCore/Base/MonoSingleton.cs

using UnityEngine;

namespace BigSpace.XRCore.Base
{
    public abstract class MonoSingleton<T> : MonoBehaviour where T : MonoSingleton<T>
    {
        private static T _instance;
        private static readonly object _lock = new object();

        public static T Instance
        {
            get
            {
                if (_instance == null)
                {
                    lock (_lock)
                    {
                        _instance = FindObjectOfType<T>();
                        if (_instance == null)
                        {
                            GameObject singletonObject = new GameObject(typeof(T).Name);
                            _instance = singletonObject.AddComponent<T>();
                            DontDestroyOnLoad(singletonObject);
                        }
                    }
                }
                return _instance;
            }
        }

        protected virtual void Awake()
        {
            if (_instance == null)
            {
                _instance = this as T;
                DontDestroyOnLoad(gameObject);
            }
            else if (_instance != this)
            {
                Destroy(gameObject);
            }
        }

        protected virtual void OnDestroy()
        {
            if (_instance == this)
            {
                _instance = null;
            }
        }
    }
}