[Unity] MonoBehaviourSingleton

MonoBehaviourSingleton.cs

using UnityEngine;
using System.Collections;

public class MonoBehaviourSingleton<T> : MonoBehaviour where T : MonoBehaviour
{
  private static T _instance = null;

  private static bool _applicationIsQuitting = false;

  [RuntimeInitializeOnLoadMethod]
  private static void RunOnStart()
  {
    Application.quitting += () => _applicationIsQuitting = true;
  }

  public static T Instance
  {
    get
    {
      if (_applicationIsQuitting)
        return null;

      if (ReferenceEquals(_instance, null))
      {
        _instance = (T)FindObjectOfType(typeof(T));
        if (ReferenceEquals(_instance, null))
        {
          _instance = (new GameObject(typeof(T).Name)).AddComponent<T>();
        }

        DontDestroyOnLoad(_instance.gameObject);
      }

      return _instance;
    }
  }
}