Tab Bar — 什么是标签栏，移动应用中的标签栏面板

import UIKit

class MainTabBarController: UITabBarController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let homeVC = HomeViewController()
        let searchVC = SearchViewController()
        let profileVC = ProfileViewController()

        homeVC.tabBarItem = UITabBarItem(
            title: "首页",
            image: UIImage(systemName: "house.fill"),
            tag: 0
        )
        searchVC.tabBarItem = UITabBarItem(
            title: "搜索",
            image: UIImage(systemName: "magnifyingglass"),
            tag: 1
        )
        profileVC.tabBarItem = UITabBarItem(
            title: "个人资料",
            image: UIImage(systemName: "person.circle.fill"),
            tag: 2
        )

        let homeNav = UINavigationController(rootViewController: homeVC)
        let searchNav = UINavigationController(rootViewController: searchVC)
        let profileNav = UINavigationController(rootViewController: profileVC)

        viewControllers = [homeNav, searchNav, profileNav]
    }
}

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val navView: NavigationBarView = binding.navView
        val navController = findNavController(R.id.nav_host_fragment)

        // 将 BottomNavigation 连接到 NavController
        navView.setupWithNavController(navController)

        // 在通知标签上配置徽章
        val badge = navView.getOrCreateBadge(R.id.navigation_notifications)
        badge.isVisible = true
        badge.number = 12
    }
}

// 在 iOS 中自定义 Tab Bar
let appearance = UITabBarAppearance()
appearance.backgroundColor = .systemBackground
appearance.stackedLayoutAppearance.normal.titleTextAttributes = [
    .foregroundColor: UIColor.secondaryLabel,
    .font: UIFont.systemFont(ofSize: 11)
]
appearance.stackedLayoutAppearance.selected.titleTextAttributes = [
    .foregroundColor: UIColor.systemBlue,
    .font: UIFont.boldSystemFont(ofSize: 12)
]
tabBar.standardAppearance = appearance.

// 在 Android 中自定义 BottomNavigationView
val navView = findViewById<NavigationBarView>(R.id.nav_view)

with (navView) {
    labelVisibilityMode = NavigationBarView.LABEL_VISIBILITY_LABELED
    itemActiveIndicatorStyle = R.style.CustomIndicator
    itemRippleColor = ColorStateList.valueOf(
        Color.valueOf("#FFE0B2")
    )
}

// 在 XML 中：app:menu="@menu/bottom_nav_menu"
// 在 XML 中：app:itemActiveIndicatorStyle="@style/Widget.Material3.BottomNavigationView.ActiveIndicator"