Singleton unity https://gamedev.stackexchange.com/questions/116009/in-unity-how-do-i-correctly-implement-the-singleton-pattern

singleton.cs

public abstract class Singleton<T> : MonoBehaviour where T : class
{
    private static T _instance;

    public static T Instance { get { return _instance; } }

    protected virtual void Awake()
    {
        if (_instance != null && _instance != this as T)
        {
            Destroy(this.gameObject);
        }
        else
        {
            _instance = this as T;
        }
    }
}
/*public class SoundEventService : Singleton<SoundEventService>
{
    public event Action OnObstacleHit;

    public void CallOnObstacleHit()
        => OnObstacleHit?.Invoke();

    public event Action OnButtonClick;

    public void CallOnButtonClick()
        => OnButtonClick?.Invoke();

    protected override void Awake()
    {
        base.Awake();
    }
}*/

public abstract class SingletoneBase<T> : MonoBehaviour
    where T : class
{
    /// <summary>
    /// SingletoneBase instance back field
    /// </summary>
    private static T instance = null;
    /// <summary>
    /// SingletoneBase instance
    /// </summary>
    public static T Instance
    {
        get
        {
            if (instance == null)
            {
                instance = GameObject.FindObjectOfType(typeof(T)) as T;
                if (instance == null)
                    Debug.LogError("SingletoneBase<T>: Could not found GameObject of type " + typeof(T).Name);
            }
            return instance;
        }
    }
}
 

public class SomeClass : MonoBehaviour {
    private static SomeClass _instance;

    public static SomeClass Instance { get { return _instance; } }


    private void Awake()
    {
        if (_instance != null && _instance != this)
        {
            Destroy(this.gameObject);
        } else {
            _instance = this;
        }
    }
}


public class UnitySingletonPersistent : MonoBehaviour
    where T : Component
{
    private static T instance;
    public static T Instance {
        get {
            if (instance == null) {
                instance = FindObjectOfType<T> ();
                if (instance == null) {
                    GameObject obj = new GameObject ();
                    obj.hideFlags = HideFlags.HideAndDontSave;
                    instance = obj.AddComponent<T> ();
                }
            }
            return instance;
        }
    }
 
    public virtual void Awake ()
    {
        DontDestroyOnLoad (this.gameObject);
        if (instance == null) {
            instance = this as T;
        } else {
            Destroy (gameObject);
        }
    }
}


public class GenericSingletonClass<T> : MonoBehaviour where T : Component
{
    private static T instance;
    public static T Instance {
      get {
        if (instance == null) {
           instance = FindObjectOfType<T> ();
           if (instance == null) {
             GameObject obj = new GameObject ();
             obj.name = typeof(T).Name;
             instance = obj.AddComponent<T>();
           }
        }
       return instance;
      }
    }
 
    public virtual void Awake ()
    {
       if (instance == null) {
         instance = this as T;
         DontDestroyOnLoad (this.gameObject);
    } else {
      Destroy (gameObject);
    }
  }
}