目标c:选项卡栏不显示

// 创建 Tab Bar Controller
UITabBarController *tabBarController = [[UITabBarController alloc] init];

// 创建子视图控制器
UIViewController *firstViewController = [[UIViewController alloc] init];
firstViewController.tabBarItem.title = @"First";
firstViewController.tabBarItem.image = [UIImage imageNamed:@"first_icon"];

UIViewController *secondViewController = [[UIViewController alloc] init];
secondViewController.tabBarItem.title = @"Second";
secondViewController.tabBarItem.image = [UIImage imageNamed:@"second_icon"];

// 将子视图控制器添加到 Tab Bar Controller
tabBarController.viewControllers = @[firstViewController, secondViewController];

// 将 Tab Bar Controller 设置为根视图控制器
self.window.rootViewController = tabBarController;
[self.window makeKeyAndVisible];

self.tabBarController.tabBar.hidden = NO;

firstViewController.tabBarItem = [[UITabBarItem alloc] initWithTitle:@"First" image:[UIImage imageNamed:@"first_icon"] tag:0];
secondViewController.tabBarItem = [[UITabBarItem alloc] initWithTitle:@"Second" image:[UIImage imageNamed:@"second_icon"] tag:1];

#import "AppDelegate.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    // 创建 Tab Bar Controller
    UITabBarController *tabBarController = [[UITabBarController alloc] init];

    // 创建子视图控制器
    UIViewController *firstViewController = [[UIViewController alloc] init];
    firstViewController.view.backgroundColor = [UIColor whiteColor];
    firstViewController.tabBarItem = [[UITabBarItem alloc] initWithTitle:@"First" image:[UIImage imageNamed:@"first_icon"] tag:0];

    UIViewController *secondViewController = [[UIViewController alloc] init];
    secondViewController.view.backgroundColor = [UIColor whiteColor];
    secondViewController.tabBarItem = [[UITabBarItem alloc] initWithTitle:@"Second" image:[UIImage imageNamed:@"second_icon"] tag:1];

    // 将子视图控制器添加到 Tab Bar Controller
    tabBarController.viewControllers = @[firstViewController, secondViewController];

    // 将 Tab Bar Controller 设置为根视图控制器
    self.window.rootViewController = tabBarController;
    [self.window makeKeyAndVisible];

    return YES;
}

@end