ios - Firebase 和 Swift - 延迟更改 ViewController 直到读取数据

Question

我实现了一个登录，每次用户登录时从实时数据库加载数据。当用户成功登录时，正在读取数据 - 问题是 AppDelegate更改 ViewController 的速度比读取数据的速度快。因此，在应用程序再次关闭之前不会显示任何内容。

有没有办法延迟 View 的更改，直到读取数据？

didFinishLaunchingOptions() 在 AppDelegate 中:

let authListener = Auth.auth().addStateDidChangeListener { auth, user in

    let storyboard = UIStoryboard(name: "Main", bundle: nil)

    if user != nil {
        let controller = storyboard.instantiateViewController(withIdentifier: "RootPageViewController") as! RootPageViewController
        self.window?.rootViewController = controller
        self.window?.makeKeyAndVisible()
    } else {
        let vc = storyboard.instantiateViewController(withIdentifier: "SettingsTableViewController") as! SettingsTableViewController
        vc.runResetData()

        let controller = storyboard.instantiateViewController(withIdentifier: "ProfileViewController") as! ProfileViewController
        self.window?.rootViewController = controller
        self.window?.makeKeyAndVisible()
    }
}

登录 View Controller :

@IBAction func login(_ sender: Any) {
    guard let email = emailInput.text else { return }
    guard let password = passwordInput.text else { return }

    Auth.auth().signIn(withEmail: email, password: password) { user, error in
        if error == nil && user != nil {
            self.readData()
            self.dismiss(animated: false, completion: nil)
        } else {
            print("Error logging in: ", error!.localizedDescription)

            let alert = UIAlertController(title: "Fehler beim Einloggen", message: error!.localizedDescription, preferredStyle: .alert)
            alert.addAction(UIAlertAction(title: "Verstanden", style: .default, handler: nil))
            self.present(alert, animated: true, completion: nil)
        }
    }
} 

func readData() {
    guard let uid = Auth.auth().currentUser?.uid else { return }
    let databaseRef = Database.database().reference()

    databaseRef.child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in

        let value = snapshot.value as? NSDictionary
        let monthlyStartKmData = value?["monthlyStartKm"] as? Int ?? 0
        let currentKmData = value?["currentKm"] as? Int ?? 0
        ...


        startKm = monthlyStartKmData
        currentKm = currentKmData
        ...


    }) { (error) in
        print(error.localizedDescription)
    }

}

Answer 1

不，你不能，因为对 listen 的调用是异步的，所以它在设置 rootVC 时延迟运行，你需要显示一个加载器，比如

 let vc = UIViewController()
 vc.view.backgroundColor = .red
 self.window?.rootViewController = vc
 self.window?.makeKeyAndVisible()    
 let authListener = Auth.auth().addStateDidChangeListener { auth, user in 
   .....
 }

在 AppDelegate 内部

if FIRAuth.auth().currentUser != nil {
   // go to home , if you went before you should have km month values cached 
}
else {
  // go to login
}