选项卡栏在swift中显示错误的选定索引

在我的应用程序中，有四个选项卡的选项卡栏。通过单击显示不同视图控制器的任何选项卡。单击第三和第四选项卡，将显示相同的viewcontroler。在创建选项卡栏的过程中，我创建了同一viewcontroler的不同对象。并在第三和第四个选项卡中显示它们

 func configureViewController() {
        let storyBoard = UIStoryboard(name: "Main", bundle: nil)
        let PatientListViewController = storyBoard.instantiateViewController(withIdentifier: "PatientListViewController") as? PatientListViewController
        let DeliveryFormNavigationController = configureNavController(unselectedImage: imageLiteral(resourceName: "DeliveryFormTabUnselected") , selectedImage: imageLiteral(resourceName: "DeliveryFormTabSelected"), rootViewController: PatientListViewController!)
        
        let PatientListViewController1 = storyBoard.instantiateViewController(withIdentifier: "PatientListViewController") as? PatientListViewController
        let StockAndBillNavigationController = configureNavController(unselectedImage:  imageLiteral(resourceName: "StockAndBillUnselected"), selectedImage:  imageLiteral(resourceName: "StockAndBillSelected"), rootViewController: PatientListViewController1!)
        
    
        let storyBoard1 = UIStoryboard(name: "Swipe", bundle: nil)
        let allPdfFilesVC = storyBoard1.instantiateViewController(withIdentifier: "AllPdfFilesViewController") as? AllPdfFilesViewController
        let allPdfNavigationController = configureNavController(unselectedImage:  imageLiteral(resourceName: "AllPdfUnselected"), selectedImage:  imageLiteral(resourceName: "AllPdfSelected"), rootViewController: allPdfFilesVC!)
    
        
        let dashBoardViewController =
            storyboard?.instantiateViewController(withIdentifier: "DashBoardViewController")
        let DashBoardVC =
            storyboard?.instantiateViewController(withIdentifier: "DashBoardVC")
        let dashBoardNavigationController = configureNavController(unselectedImage:  imageLiteral(resourceName: "DashboardTabUnselected"), selectedImage:   imageLiteral(resourceName: "DashboardTabSelected"), rootViewController: DashBoardVC!)
        
        // Add all the view instances to the tabbar
            
        viewControllers = [dashBoardNavigationController, allPdfNavigationController, DeliveryFormNavigationController,  StockAndBillNavigationController]
        guard let items = tabBar.items else {return}
        print(items)
        for item in items {
            if #available(iOS 13, *) {
                item.imageInsets = UIEdgeInsets(top: 6, left: 0, bottom: 0, right: 0)

                self.additionalSafeAreaInsets = UIEdgeInsets(top: 20, left: 0, bottom: 0, right: 0)
                item.title = nil
            }

        }
        
    }

但当我进入第三和第四个选项卡时，有时会显示选中的索引，如果是“2”，有时是“3”

class PatientListViewController: UIViewController {

override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
 if let app = UIApplication.shared.delegate as? AppDelegate, let window = app.window {
            if let tabBarController = window.rootViewController as? UITabBarController {
                if tabBarController.selectedIndex == 2{
                    pdfType = "Delivery Form"
                }
                else if tabBarController.selectedIndex == 3{
                    pdfType = "Stock and bill form"
                }
               }
        }
}
}