tabBarController(_:sidebar:itemFor:)

Return a UITabSidebarItem for the specified item request. When created, the item will be preconfigured to the appropriate defaults for its given content. If this method is not implemented, a default sidebar item will be provided for the request.

optional func tabBarController(_ tabBarController: UITabBarController, sidebar: UITabBarController.Sidebar, itemFor request: UITabSidebarItem.Request) -> UITabSidebarItem