objective-c – 如何向导航控制器添加按钮

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    UIViewController *viewController1,*viewController2,*viewController3,*viewController4;

    viewController1 = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
    viewController2 = [[DisplayAllImagesController alloc] initWithNibName:@"DisplayAllImagesController" bundle:nil];
    viewController3 = [[EmptyView alloc] initWithNibName:@"EmptyView" bundle:nil];
    viewController4 = [[ListView alloc] initWithNibName:@"ListView" bundle:nil];



    self.tabBarController = [[UITabBarController alloc] init];
    self.tabBarController.viewControllers = [NSArray arrayWithObjects:viewController2,viewController1,viewController3,viewController4,nil];
    self.tabBarController.title = @"Title";

    self.navController = [[UINavigationController alloc]
                          initWithRootViewController:self.tabBarController];
    self.window.rootViewController = self.navController;
    [self.window makeKeyAndVisible];
    return YES;
}

所以,请让我知道如何添加按钮到导航控制器…请…