IOS中如何调用Rootviewcontroller？

我希望在ios应用中能实现查看用户是注册用户还是新用户，如果还没注册的用户，就会转到注册页面。代码如下：

if (user != register){

        RegisterViewController *registerViewController = [[RegisterViewController alloc] init];
                RearViewController *rearViewController = [[RearViewController alloc] init];

        UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:registerViewController];

        self.viewController = revealController;

        self.window.rootViewController = self.viewController;

        self.window makeKeyAndVisible];
    }else {

FrontViewController *frontViewController = [[FrontViewController alloc] init];
            RearViewController *rearViewController = [[RearViewController alloc] init];

UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:frontViewController];

RevealController *revealController = [[RevealController alloc] initWithFrontViewController:navigationController rearViewController:rearViewController];

self.viewController = revealController;

self.window.rootViewController = self.viewController;

[self.window makeKeyAndVisible];

}

如果用户没注册，就会进入注册页面

但是有问题，等用户注册完了，在屏幕上方就会出现两个导航控制器。
我用下面的代码将已注册用户导入主页面：

[[self navigationController] pushViewController:revealController animated:YES];

不知道问题在哪里~

从网上搜来的，

[[UIApplication sharedApplication] keyWindow].rootViewController = revealController;

设置另一个root view controller，看看能实现不？