錯誤：類型'AppDelegate？'的值沒有成員「出席」

Question

我得到的

Value of type 'AppDelegate?' has no member 'present'

，當我試圖讓我的用戶登錄，即使應用了退出的錯誤。

這是我的視圖控制器，任何想法如何讓我的用戶登錄？爲什麼我得到這個錯誤？

我在我的代碼中使用Firebase作爲我的數據庫。

LoginViewController.swift

import UIKit 
import Firebase 

class LoginViewController: UIViewController, UITextFieldDelegate { 

    @IBOutlet weak var emailField: UITextField! 
    @IBOutlet weak var pwField: UITextField! 




    func createAlert(title:String, message:String) { 

     let alert=UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert) 


     alert.addAction(UIAlertAction(title: "error" , style: UIAlertActionStyle.default, handler: { (action) in alert.dismiss(animated: true, completion: nil) 
     })) 

     self.present(alert, animated:true, completion: nil) 
    } 





    /* @IBAction func emailKeyboardField(_ sender: Any) { 

     hideKeyboard() 
    } 

    func hideKeyboard() { 
     emailField.resignFirstResponder() 
     pwField.resignFirstResponder() 

    } 
    */ 

    override func viewDidLoad() { 
     super.viewDidLoad() 

     emailField.delegate = self 


     // Do any additional setup after loading the view. 
    } 



    func emailKeyField(_ emailField: UITextField) -> Bool { 
     self.view.endEditing(true) 


     return true 
    } 


    @IBAction func loginPressed(_ sender: Any) { 

     guard emailField.text != "", pwField.text != "" else {return} 

     FIRAuth.auth()?.signIn(withEmail: emailField.text!, password: pwField.text!, completion: { (user, error) in 

      if let error = error { 
       print(error.localizedDescription) 

       self.createAlert(title: "Error", message: "We could not locate your account. Check your email and password.") 
      } 


      if let user = user { 
       let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "usersVC") 

       self.present(vc, animated: true, completion: nil) 
      } 
     }) 


    } 


} 

AppDelegate.swift

import UIKit 
import Firebase 


@UIApplicationMain 
class AppDelegate: UIResponder, UIApplicationDelegate, UIImagePickerControllerDelegate, UINavigationControllerDelegate { 

    var window: UIWindow? 
    var actIdc = UIActivityIndicatorView(activityIndicatorStyle: .whiteLarge) 
    var container: UIView! 
    private let auth = FIRAuth.auth() 

    class func instance() -> AppDelegate { 
     return UIApplication.shared.delegate as! AppDelegate 
    } 


    func showActivityIndicator() { 
     if let window = window { 
      container = UIView() 
      container.frame = window.frame 
      container.center = window.center 
      container.backgroundColor = UIColor(white: 0, alpha: 0.8) 

      actIdc.frame = CGRect(x: 0, y: 0, width: 40, height: 40) 
      actIdc.hidesWhenStopped = true 
      actIdc.center = CGPoint(x: container.frame.size.width/2, y: container.frame.size.height/2) 

      container.addSubview(actIdc) 
      window.addSubview(container) 

      actIdc.startAnimating() 
     } 
    } 

    func dismissActivityIndicatos() { 
     if let _ = window { 
      container.removeFromSuperview() 
     } 
    } 

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool { 



       auth?.addStateDidChangeListener { [weak self] (_, user) in 

        if let user = user { 
         let vc = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "usersVC") 

         self.present(vc, animated: true, completion: nil) //error on this line 
         // user is already logged in 
        } else { 
         // user is not logged in 
        } 


     } 
     FIRApp.configure() 
     return true 
    } 


    func applicationWillResignActive(_ application: UIApplication) { 
     // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state. 
     // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game. 
    } 

    func applicationDidEnterBackground(_ application: UIApplication) { 
     // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later. 
     // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits. 
    } 

    func applicationWillEnterForeground(_ application: UIApplication) { 
     // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background. 
    } 

    func applicationDidBecomeActive(_ application: UIApplication) { 
     // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface. 
    } 

    func applicationWillTerminate(_ application: UIApplication) { 
     // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:. 
    } 


} 

任何和所有幫助將不勝感激。

Answer 1

應用程序委託不屬於ViewController類型，因此它沒有現有方法在其上顯示視圖。相反，你可以做的是使用它的窗口顯示一個視圖，如：

let storyboard : UIStoryboard = UIStoryboard(name: "Main", bundle: nil) 
    let homeC = storyboard.instantiateViewController(withIdentifier: "YOUR_VIEWCONTROLLER_IDENTIFIER_IN_STORYBOARD") as? HomeC 
    if homeC != nil { 
     homeC!.view.frame = (self.window!.frame) 
     self.window!.addSubview(homeC!.view) 
     self.window!.bringSubview(toFront: homeC!.view) 
    }