其視圖不在窗口層次結構中的UIAlertController

Question

我試圖用Swift和Parse創建一個應用程序。我使用的Xcode 7和斯威夫特2 我想顯示提示信息時，用戶的登錄失敗，這裏是我的功能：

func logInViewController(logInController: PFLogInViewController, didFailToLogInWithError error: NSError?){ 
    let alertLoginFailed = UIAlertController(title: "Login Failed", message: "Your username or password is invalid!", preferredStyle: UIAlertControllerStyle.Alert) 
    alertLoginFailed.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)) 
    self.presentViewController(alertLoginFailed, animated: true, completion: nil) 
    print("Login failed.........!") 
} 

但在模擬器中運行時，我得到這個錯誤：

2015-10-02 11:32:39.988 RedString[2089:886501] Warning: Attempt to present <UIAlertController: 0x7a934400> on <MyProject.ViewController: 0x7b985150> whose view is not in the window hierarchy! 
Login failed.........! 

我已經使用了它，但我沒有找到明確的解決方案。

這裏是我的全班同學：

import UIKit 
import Parse 
import ParseUI 
class ViewController: UIViewController, PFLogInViewControllerDelegate, PFSignUpViewControllerDelegate { 

    override func viewDidLoad() { 
     super.viewDidLoad() 
    } 

    override func viewDidAppear(animated: Bool) { 
     self.setupLoginView() 
    } 

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

    func logInViewController(logInController: PFLogInViewController, didLogInUser user: PFUser){ 
     self.dismissViewControllerAnimated(true, completion: nil) 
    } 

    func logInViewController(logInController: PFLogInViewController, didFailToLogInWithError error: NSError?){ 
     let alertLoginFailed = UIAlertController(title: "Login Failed", message: "Your username or password is invalid!", preferredStyle: UIAlertControllerStyle.Alert) 
     alertLoginFailed.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)) 
     self.presentViewController(alertLoginFailed, animated: true, completion: nil) 
     print("Login failed.........!") 
    } 

    func signUpViewController(signUpController: PFSignUpViewController, didSignUpUser user: PFUser){ 
     self.dismissViewControllerAnimated(true, completion: nil) 
    } 

    func signUpViewController(signUpController: PFSignUpViewController, didFailToSignUpWithError error: NSError?){ 
     print("Sign up failed.........!") 
    } 

    func setupLoginView(){ 
     if(PFUser.currentUser() == nil){ 
      let loginViewController = PFLogInViewController() 
      loginViewController.delegate = self 
      let signUpViewController = PFSignUpViewController() 
      signUpViewController.delegate = self 
      loginViewController.logInView!.logo = UIImageView(image: UIImage(named:"logo.png")) 

      loginViewController.signUpController = signUpViewController 
      self.presentViewController(loginViewController, animated: true, completion: nil) 
     }else{ 
      print("login as: " + PFUser.currentUser()!.username!) 
      //prepare new view here 
     } 

    } 
} 

Answer 1

你得叫presentViewController:animated:completion登錄視圖控制器上。

下面是一個簡化版本的類的向你展示我的意思：

class ViewController: UIViewController { 
    weak var loginViewController: UIViewController? 

    func setupLoginViewController() { 
     let loginVC = PFLogInViewController() 
     // setup loginVC 
     loginViewController = loginVC // store the reference 
    } 

    func loginDidFail() { 
     let alertVC = UIAlertController(...) 
     // setup alertVC 
     loginViewController?.presentViewController(...) // present the alert from the login view controller 
    } 
} 

Answer 2

時

func logInViewController(logInController: PFLogInViewController, didFailToLogInWithError error: NSError?){ 
     let alertLoginFailed = UIAlertController(title: "Login Failed", message: "Your username or password is invalid!", preferredStyle: UIAlertControllerStyle.Alert) 
     alertLoginFailed.addAction(UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)) 
     self.presentViewController(alertLoginFailed, animated: true, completion: nil) 
     print("Login failed.........!") 
    } 

被調用，您的視圖控制器是不是在屏幕上。因此，您既可以

• 駁回logInViewController，則顯示警報，並通過 setUpLogInView的處理程序。

• 或在上面的功能，嘗試logInController.presentViewController 代替self.presentViewController

Answer 3

我不得不在Objective-C同樣的問題，當父窗口尚未繪製到屏幕上它發生。我通過調用viewDidAppear中的代碼而不是viewDidLoad來解決問題。請參閱UIAlert error, whose view is not in the window hierarchy