UINavigationController和UITabBarController同时使用设置vc.navigationItem.title无效

想要设置一个同时使用UINavigationController和UITabBarController的结构，我在AppDelegate.m中这样写：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
  
//自定义的UITabBarController
    myTabBarController * myTabBar = [[myTabBarController alloc]init];
    myTabBar.view.bounds=[UIScreen mainScreen].bounds;
    UIWindow *window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
    UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:myTabBar];
    window.rootViewController = nav;
    self.window = window;
    [window makeKeyAndVisible];
    return YES;
}

然后在myTabBarController.m中

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    [self addChildViewController:childVCMain(@"首页", @"user_00084", 0)];
    [self addChildViewController:childVCTool(@"工具", @"Tools_00028", 1)];
    [self addChildViewController:childVCMine(@"我的", @"drop", 2)];
    self.tabBar.tintColor = [UIColor colorWithRed:234/255.0 green:111/255.0 blue:90/255.0 alpha:1];
    if (@available(iOS 10.0, *)) {
        self.tabBar.unselectedItemTintColor = [UIColor colorWithRed:124/255.0 green:99/255.0 blue:86/255.0 alpha:1];
    } else {
        // Fallback on earlier versions
    }
    
}

UIViewController *childVCMain(NSString *title,NSString *imageName,NSInteger tag){
    mainViewController * vc = [[mainViewController alloc]init];
    vc.view.backgroundColor = [UIColor redColor];
    vc.tabBarItem = [[UITabBarItem alloc] initWithTitle:title image:[UIImage imageNamed:imageName] tag:tag];
    return vc;
    
}
UIViewController *childVCTool(NSString *title,NSString *imageName,NSInteger tag){
    toolViewController * vc = [[toolViewController alloc]init];
    vc.view.backgroundColor = [UIColor yellowColor];
    vc.tabBarItem = [[UITabBarItem alloc]initWithTitle:title image:[UIImage imageNamed:imageName] tag:tag];
    return vc;
    
}
UIViewController *childVCMine(NSString *title,NSString *imageName,NSInteger tag){
    mineViewController * vc = [[mineViewController alloc]init];
    vc.view.backgroundColor = [UIColor blueColor];
    vc.navigationItem.title = @"个人中心";
    vc.tabBarItem = [[UITabBarItem alloc]initWithTitle:title image:[UIImage imageNamed:imageName] tag:tag];
    return vc;
    
}

结果这样三个页面同时使用一个UINavigationController，造成不显示页面的navigationItem.title。所以每个页面都各自分配一个UINavigationController，问题解决。

//删掉AppDelegate中的
UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:myTabBar];

在每个自定义childVC中增加

UINavigationController *nvc = [[UINavigationController alloc]initWithRootViewController:vc];

return nvc;

问题解决。。。还是对结构不熟练才会出这样的问题