IOS --项目开始添加导航栏

self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.window.backgroundColor = [UIColor whiteColor];
    
    RootViewController *rootVC = [[RootViewController alloc] init];
    UINavigationController *nvc = [[UINavigationController alloc] initWithRootViewController:rootVC];
    self.window.rootViewController = nvc;
    
    [self.window makeKeyAndVisible];