public abstract class Singleton<T> where T : class, new()
{
  private static T instance = null;

  private static readonly object locker = new object();

  public static T Instance
  {
    get
    {
      lock (locker)
      {
        if (instance == null)
          instance = new T();
        return instance;
      }
    }
  }
}

using UnityEngine;

public abstract class MonoSingleton <T>: MonoBehaviour where T:MonoBehaviour
{
  private static T instance = null;

  private static readonly object locker = new object();

  private static bool bAppQuitting;

  public static T Instance
  {
    get
    {
      if (bAppQuitting)
      {
        instance = null;
        return instance;
      }

      lock (locker)
      {
        if (instance == null)
        {
          instance = FindObjectOfType<T>();
          if (FindObjectsOfType<T>().Length > 1)
          {
            Debug.LogError("不應(yīng)該存在多個(gè)單例！");
            return instance;
          }

          if (instance == null)
          {
            var singleton = new GameObject();
            instance = singleton.AddComponent<T>();
            singleton.name = "(singleton)" + typeof(T);
            singleton.hideFlags = HideFlags.None;
            DontDestroyOnLoad(singleton);
          }
          else
            DontDestroyOnLoad(instance.gameObject);
        }
        instance.hideFlags = HideFlags.None;
        return instance;
      }
    }
  }

  private void Awake()
  {
    bAppQuitting = false;
  }

  private void OnDestroy()
  {
    bAppQuitting = true;
  }
}