LogoutPressed.swift

    @IBAction func logoutPressed(_ sender: UIButton) {
        // 畫面顯示怪怪的，再確認
        do {
            try Auth.auth().signOut()
//            navigationController?.popToRootViewController(animated: true)
            var rootVC = self.presentingViewController
            while let parent = rootVC?.presentingViewController {
                rootVC = parent
            }
            rootVC?.dismiss(animated: true, completion: nil)
            print("logout success!")
        } catch let signOutError as NSError {
            print ("Error signing out: %@", signOutError)
        }
    }