private void ShowMainScreen()
 {
     if (ShowMainScreenAction != null)
     {
         ShowMainScreenAction.Invoke();
     }
 }
 private void ShowMainScreen()
 {
     if (ShowMainScreenAction != null)
     {
         MiddleModel = MiddleModel ?? new MiddleClassModel();
         ShowMainScreenAction.Invoke();
     }
 }