ios - 当包含 firebase 时，其 View 不在窗口层次结构中的 LoginViewController 上的 UIAlertController

Question

嗨，每当我输入在 Firebase 数据库中检查的错误登录信息详细信息时，我想显示一个警报 Controller 以阻止它进入应用程序。但是我收到一条错误消息，说 alertviewcontroller 不是窗口层次结构。当我在 firebase 数据 block 之外调用该函数时，我没有收到该错误。有人可以解释如何解决这个问题吗？

{
import UIKit
import Firebase

class LoginViewController: UIViewController {

    let BASE_REF = Firebase(url: "https://cal-sap.firebaseio.com/?page=Auth")
    let USER_REF = Firebase(url: "https://cal-sap.firebaseio.com/?page=Auth/users")

    let gradientLayer = CAGradientLayer()
    @IBOutlet weak var Email: UITextField!
    @IBOutlet weak var Password: UITextField!

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        /*let defaults = NSUserDefaults.standardUserDefaults()
        let name = defaults.stringArrayForKey("uid")
        if name != nil && USER_REF.authData.uid != nil {
            self.performSegueWithIdentifier("LoggedinView", sender: self)
            print(name);
        }
    */
        if NSUserDefaults.standardUserDefaults().valueForKey("uid") != nil && DataService.dataService.CURRENT_USER_REF.authData != nil {
            self.performSegueWithIdentifier("LoggedinView", sender: nil)
        }

    }

    override func viewDidLoad() {
        super.viewDidLoad()

        self.view.backgroundColor = UIColor.grayColor()

        gradientLayer.frame = self.view.bounds


        let color1 = UIColor(red: (69/255.0), green: (69/255.0), blue:(69/255.0), alpha: 0.05).CGColor as CGColorRef
        let color2 = UIColor(red: (71/255.0), green: (71/255.0), blue:(71/255.0), alpha: 0.05).CGColor as CGColorRef
        let color3 = UIColor(red: (200/255.0), green: (200/255.0), blue:(200/255.0), alpha: 0.05).CGColor as CGColorRef
        let color4 = UIColor.whiteColor().CGColor as CGColorRef
        gradientLayer.colors = [color1,color2,color3,color4]

        gradientLayer.locations = [0.0,0.25,0.75,1.0]


        self.view.layer.addSublayer(gradientLayer)

        let userimageView = UIImageView();
        let userimage = UIImage(named: "Email.png");
        userimageView.image = userimage;
        Email.leftView = userimageView
        Email.leftViewMode = UITextFieldViewMode.Always
        userimageView.frame = CGRectMake(20, 10, 15, 20)

        let passimageView = UIImageView();
        let passimage = UIImage(named: "lock.png");
        passimageView.image = passimage;
        Password.leftView = passimageView
        Password.leftViewMode = UITextFieldViewMode.Always
        passimageView.frame = CGRectMake(15, 10, 15, 20)


        // Do any additional setup after loading the view.


     }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.


     }


    @IBAction func LoginButtonTapped(sender: AnyObject) {



        if(Email != "" || Password != ""){
            /*USER_REF.authUser(Email.text, password:Password.text) {
                error, authData in
                if error != nil {
                    self.displayAlertMessage("Information not valid. Please enter again.");
                    print("user not defined");
                } else {
                    NSUserDefaults.standardUserDefaults().setValue(authData.uid, forKey: "uid")
                }
            }
            */
            DataService.dataService.BASE_REF.authUser(Email.text, password: Password.text, withCompletionBlock: { error, authData in

                if error != nil {
                    print(error)
                    self.displayAlertMessage("Information invalid. Please enter again.")
                } else {

                    // Be sure the correct uid is stored.

                        NSUserDefaults.standardUserDefaults().setValue(authData.uid, forKey: "uid")

                    // Enter the app!

                    self.performSegueWithIdentifier("CurrentlyLoggedIn", sender: nil)
                }
            })
        }
        else{
            self.displayAlertMessage("Please fill all the fields")
        }
    }

    func displayAlertMessage(usermessage: String)
    {
        let MyAlert = UIAlertController(title: "Alert", message: usermessage, preferredStyle: UIAlertControllerStyle.Alert)

        let okAction = UIAlertAction(title: "Ok", style: UIAlertActionStyle.Default, handler: nil)

        MyAlert.addAction(okAction)

            self.presentViewController(MyAlert, animated: true, completion: nil)
    }


    }
}

#DataService.swift 文件

{
import Foundation
import Firebase

class DataService {
    static let dataService = DataService()

    private var _BASE_REF = Firebase(url: "https://cal-sap.firebaseio.com/?page=Auth")
    private var _USER_REF = Firebase(url: "https://cal-sap.firebaseio.com/?page=Auth/users")
    private var _EVENT_REF = Firebase(url: "https://cal-sap.firebaseio.com/?page=Auth/users/events")

    var BASE_REF: Firebase {
        return _BASE_REF
    }

    var USER_REF: Firebase {
        return _USER_REF
    }

    var CURRENT_USER_REF: Firebase {
        let userID = NSUserDefaults.standardUserDefaults().valueForKey("uid") as! String

        let currentUser = Firebase(url: "\(BASE_REF)").childByAppendingPath("users").childByAppendingPath(userID)

        return currentUser!
    }

    var EVENT_REF: Firebase {
        return _EVENT_REF
    }


    }
}

Answer 1

如果你必须处理异步 block 中的 UI 元素，你必须在主队列中进行:

dispatch_async(dispatch_get_main_queue(), { [weak self] () -> Void in
    self?.presentViewController(MyAlert, animated: true, completion: nil)
})

我认为这会解决您的问题，但对于警报，我总是使用这些实用程序变量:

public var APP_KEY_WINDOW: UIWindow? { get { return UIApplication.sharedApplication().keyWindow } }
public var APP_ROOT_VC: UIViewController? {
    get {
        guard let root = APP_KEY_WINDOW?.rootViewController else { return nil }
        guard root.isViewLoaded() && root.view.window != nil else {
            guard let presentedVC = root.presentedViewController else { return nil }
            return presentedVC
        }
        return root
    }
}

如下:

dispatch_async(dispatch_get_main_queue(), { () -> Void in
    APP_ROOT_VC?.presentViewController(MyAlert, animated: true, completion: nil)
})