Swift 4.0 如何改变 tabBar 标签栏图片、字体颜色

方法一：
直接在 AppDelegate 的didFinishLaunchingWithOptions 方法中设置：

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        
        let nav1 = UINavigationController(rootViewController: UIViewController())
        nav1.tabBarItem = UITabBarItem(title: "首页", image: UIImage(named: "tabbar_normal1"), selectedImage: UIImage(named: "tabbar_selected1"))
        
        let nav2 =UINavigationController(rootViewController: UIViewController())
        nav2.tabBarItem = UITabBarItem(title: "消息", image: UIImage(named: "tabbar_normal2"), selectedImage: UIImage(named: "tabbar_selected2"))
        
        let nav3 = UINavigationController(rootViewController: UIViewController())
        nav3.tabBarItem = UITabBarItem(title: "我的", image: UIImage(named: "tabbar_normal3"), selectedImage: UIImage(named: "tabbar_selected3"))
        
        let nav4 = UINavigationController(rootViewController: UIViewController())
        nav4.tabBarItem = UITabBarItem(title: "更多", image: UIImage(named: "tabbar_normal4"), selectedImage: UIImage(named: "tabbar_selected4"))
        
        let tabBarCtl = UITabBarController()
        tabBarCtl.viewControllers = [nav1, nav2, nav3, nav4]
        
        for item in tabBarCtl.viewControllers! {
            // 遵循图片原始颜色，否则图片会变成系统默认的蓝色
            item.tabBarItem.selectedImage = item.tabBarItem.selectedImage!.withRenderingMode(.alwaysOriginal)
            // 修改标签栏选中时文字颜色
            item.tabBarItem.setTitleTextAttributes([NSAttributedStringKey.foregroundColor: UIColor.red], for: .selected)
            // 修改标签栏未选中时文字颜色
            item.tabBarItem.setTitleTextAttributes([NSAttributedStringKey.foregroundColor: UIColor.green], for: .normal)
        }
        
        self.window!.rootViewController = tabBarCtl
        
        return true
    }

方法二：
自定义 UITabBarController：

class CustomTabBarController: UITabBarController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // 修改标签栏的 bar 颜色
        //self.tabBar.barTintColor = UIColor.white
        // 修改标签栏的默认 tintColor，会改变图片和文字
        //self.tabBar.tintColor = UIColor.yellow
        
        // 修改标签栏选中时文字颜色、字体
        UITabBarItem.appearance().setTitleTextAttributes([NSAttributedStringKey.foregroundColor: UIColor.red, NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: 18.0)], for: .selected)
        // 修改标签栏未选中时文字颜色、字体
        UITabBarItem.appearance().setTitleTextAttributes([NSAttributedStringKey.foregroundColor: UIColor.orange, NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: 18.0)], for: .normal)
        // 设置字体偏移
        //UITabBarItem.appearance().titlePositionAdjustment = UIOffsetMake(0.0, 0.0)
        
        self.addChildVC()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    /// 添加控制器
    fileprivate func addChildVC() {
        self.setupOneChildViewController(UIViewController(), title: "首页", normalImage: "tabbar_normal1", selectedImage: "tabbar_selected1")
        self.setupOneChildViewController(UIViewController(), title: "消息", normalImage: "tabbar_normal2", selectedImage: "tabbar_selected2")
        self.setupOneChildViewController(UIViewController(), title: "我的", normalImage: "tabbar_normal3", selectedImage: "tabbar_selected3")
        self.setupOneChildViewController(UIViewController(), title: "更多", normalImage: "tabbar_normal4", selectedImage: "tabbar_selected4")
    }
    
    fileprivate func setupOneChildViewController(_ vc: UIViewController, title: String, normalImage: String, selectedImage: String) {
        let nav = UINavigationController(rootViewController: vc)
        nav.tabBarItem = UITabBarItem(title: title, image: UIImage(named: normalImage), selectedImage: UIImage(named: selectedImage))
        // 设置选中图片颜色，否则图片会变成系统默认的蓝色
        nav.tabBarItem.selectedImage = nav.tabBarItem.selectedImage!.withRenderingMode(.alwaysOriginal)
        addChildViewController(nav)
    }
    
}

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参考链接