Subject.RemoveObserver C# (CSharp) Method

    public void RemoveObserver(IObserver observer)
    {
        if (observer != null && m_ObserverList.Contains(observer))
        {
            m_ObserverList.Remove(observer);
        }
    }

 public void undo()
 {
     if (history.Peek() is DeSpawnInteraction)
     {
         s.RemoveObserver(this.GetComponent <UIManager>()._createdObject);
     }
     history.Peek().undo();
     future.Push(history.Pop());
 }