代码片段-需要登录的控制器代码实现

    // 数组中为需要登录的控制器
    private static let viewControllerClassesThatRequireUserSession: [AnyObject.Type] = [FavoritesCollectionViewController.self, CartViewController.self, AccountViewController.self]
    
        func tabBarController(tabBarController: UITabBarController, shouldSelectViewController viewController: UIViewController) -> Bool {
        // 如果用户已经登录返回true
        guard !AccountManager.defaultAccountManager.isUserLoggedIn else {
            return true
        }

        let visibleController: UIViewController

        // 判断将要跳转的控制器,是否需要登录
        if let navigationController = viewController as? UINavigationController {
            visibleController = navigationController.topViewController ?? viewController
        } else {
            visibleController = viewController
        }

        let shouldPresentSignInScreen = AppDelegate.viewControllerClassesThatRequireUserSession.contains { $0 == visibleController.dynamicType }

        if shouldPresentSignInScreen {
            SignInViewController.presentSignInViewController() { success in
                if success {
                // 登录成功,跳转到之前选择的控制器
                    self.tabBarController.selectedViewController = viewController
                }
            }

            return false
        }

        return true
    }