UITabBarController的子页面不加载xib？

Question

结构是login界面登录验证通过后跳转到uitabbarcontroller，

    UserListViewController *userListVC = [[UserListViewController alloc]init];
    DashboardViewController *dashboardVC = [[DashboardViewController alloc]init];
    ProjectOverallViewController *projectOverallVC = [[ProjectOverallViewController alloc]init];
    AlertViewController *alertVC = [[AlertViewController alloc]init];

    UIViewController *firstNavigationController = [[UINavigationController alloc] initWithRootViewController:userListVC];
    UIViewController *secondNavigationController = [[UINavigationController alloc] initWithRootViewController:dashboardVC];
    UIViewController *thirdViewController = [[UINavigationController alloc] initWithRootViewController:projectOverallVC];
    UIViewController *fourthNavigationController = [[UINavigationController alloc] initWithRootViewController:alertVC];

    RDVTabBarController *tabBarController = [[RDVTabBarController alloc] init];
    [tabBarController setViewControllers:@[firstNavigationController,secondNavigationController,thirdViewController,fourthNavigationController]];

    self.viewController = tabBarController;

其4个子界面在创建的时候勾选了xib，现在是我在4个xib文件设置其背景色无效，代码设置有效

请问大概是哪里的问题
子控制器

 -(id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.title = @"User";
    }
    return self;
}

Answer 1

对于 xib 文件中的其他元件，如果需要代码中中间使用：1. 必须对这个元件设置一个自定义的 class 名称2. 使用类似下边的代码去循环找到定义，代码类似：NSArray *nib = [[NSBundle mainBundle] loadNibNamed:@"xib_file_name" owner:self options:nil];for (id oneObject in nib) { if ([oneObject isKindOfClass:[ClassName class]]) { cell = (ClassName *) oneObject; break; }}