void OnDestroy()
 {
     if (instance == this)
     {
         instance = null;
     }
 }
 void Awake()
 {
     if (!instance)
     {
         DontDestroyOnLoad(this.gameObject);
         instance = this;
     }
     else if (instance != this)
     {
         DestroyImmediate(this.gameObject);
     }
 }