test/Assets/PerfectWorld/Scripts/Common/MonoSingleton.cs

using UnityEngine;

namespace BrewMonster
{
    public class MonoSingleton<T> : MonoBehaviour where T : MonoBehaviour
    {
        private static T _instance;
        public static T Instance
        {
            get
            {
                if (_instance == null)
                {
                    _instance = FindFirstObjectByType<T>();

                    if (_instance == null)
                    {
                        GameObject obj = new GameObject(typeof(T).Name);
                        _instance = obj.AddComponent<T>();
                    }
                }
                return _instance;
            }
        }   

        protected virtual void Awake()
        {
            _instance = this as T;
            Initialize();
        }

        /// <summary>Override this method to initialize the singleton</summary>
        protected virtual void Initialize()
        {
            
        }
    }
}