uitabbarcontroller-UITabBarController的子頁面不加載xib？

UITabBarController的子頁面不加載xib？

結構是login界面登錄驗證通過後跳轉到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個子界面在創建的時候勾選了xib，現在是我在4個xib文件設置其背景色無效，代碼設置有效

請問大概是哪裡的問題
子控制器

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

最佳回答：

對於 xib 文件中的其他元件，如果需要代碼中中間使用：1. 必須對這個元件設置一個自定義的 class 名稱2. 使用類似下邊的代碼去循環找到定義，代碼類似：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; }}