我正在尝试将UIViewController推送到导航Controller，然后将UIBarButtonItem添加到导航栏，以便我可以使用它来显示倒数计时器。UINavigationController*navController=[[SessionsharedInstance]getNavigationController];GamePlayViewController*gameController=[[GamePlayViewControlleralloc]initWithNibName:@"GamePlayViewController"bundle:nil];UIBarButt