我用的事xcode 8  也是遇到同样的问题，按照你的方法解决后 出现了新的错误 

Unknown receiver ‘ViewController’; did you mean 

老师用的xcode版本较老，最新版xcode中的代码应该这样写

AppDelegate.m文件：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    _navigationController=[[UINavigationController alloc]initWithRootViewController:[[ViewController alloc] init]];
    _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    _window.rootViewController = _navigationController;
    _window.backgroundColor = [UIColor redColor];
    [_window makeKeyAndVisible];
    return YES;
}

AppDelegate.h文件中加入属性：

@property (strong,nonatomic)UINavigationController *navigationController;