StaticResources.cs

public class StaticResources
{
  public static IState State
  {
    get { return StateClass.Instance; }
  }
  
  public interface IState
  {
  }
  
  private class StateClass : IState
  {
    private static volatile StateClass instance;
    private static object SyncRoot = new object();
    
    private StateClass()
    {
    }
    
    public static StateClass Instance
    {
      get
      {
        if (instance == null)
        {
          lock (SyncRoot)
          {
            if (instance == null)
            {
              instance = new StateClass();
            }
          }
        }
    
        return instance;
      }
    }
  }
}