尝试呈现其视图不在窗口层次结构中的 UIAlertController - Swift 错误

Question

我正在尝试创建警报，因此当用户注册然后想要重新登录时，如果密码错误，他们会收到警告，因为此时它只是执行 segue 并且尝试警报失败。我使用的是 Firebase，因此在注册时输入到 Firebase 的密码应该是用户登录时使用的密码。

import Foundation
import UIKit
import Firebase

class SignInViewController: UIViewController, UITextFieldDelegate {

@IBOutlet weak var EmailAddressTextField: UITextField!
@IBOutlet weak var PasswordTextField: UITextField!

// Do any additional setup after loading the view.
override func viewDidLoad() {
    super.viewDidLoad()

    EmailAddressTextField.delegate = self
    PasswordTextField.delegate = self
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
}

@IBAction func LogInButton(_ sender: Any) {
if (EmailAddressTextField.text != "" && PasswordTextField.text != ""){
Auth.auth().signIn(withEmail: EmailAddressTextField.text!, password: PasswordTextField.text!) { user, error in
    if error == nil {
        self.performSegue(withIdentifier: "LogInSegue", sender: nil)
    } else {
        let alert = UIAlertController(title: "Error", message: "Enter a correct email and password", preferredStyle: .alert)
        let action = UIAlertAction(title: "OK", style: .default, handler: nil)
        alert.addAction(action)
        self.present(alert, animated: true, completion: nil)
        }
     }
    }
  }
}

Answer 1

只是想和你核实一下，因为你上面的描述有点不清楚。当您输入错误的电子邮件/密码组合时，您的应用是否仍会执行“LogInSegue”（以及未能显示警报）？

如果是这样，听起来您可能已将 segue 连接到 UIButton 而不是 UIViewController。 要检查这一点，请单击情节提要中的 segue，然后查看 UIButton 是否突出显示。 如果是，则删除此 segue 并按照以下说明从视图控制器连接您的新 segue：

Answer 2

您在SignInViewController 上显示UIAlertController，所以当时SignInViewController 不在导航堆栈中。

因此，当您当时展示UIAlertController 时，请检查self.navigationController?.viewControllers 并验证它是否在堆栈中。

例如。

//check before self.presnt...
print(self.navigationController?.viewControllers)

因此，您需要确保当您在另一个必须位于导航堆栈中的视图控制器上显示视图控制器时，您将在日志中收到此消息。

尝试呈现其视图不在窗口层次结构中的 UIAlertController

使用以下函数在根视图控制器上显示警报

 func showAlert(title: String, msg: String, actions:[UIAlertAction]?) {

    var actions = actions
    let alertVC = UIAlertController(title: title, message: msg, preferredStyle: .alert)

    if actions == nil {
        actions = [UIAlertAction(title: "OK", style: .default, handler: nil)]
    }

    for action in actions! {
        alertVC.addAction(action)
    }

    if let rootVC = UIApplication.shared.delegate?.window??.rootViewController {
        rootVC.present(alertVC, animated: true, completion: nil)
    } else {
        print("Root view controller is not set.")
    }
}

用法

self.showAlert(title: "My App", msg: "your message", actions: nil)

你需要像这样在你的代码中使用它...

class SignInViewController: UIViewController, UITextFieldDelegate {

@IBOutlet weak var EmailAddressTextField: UITextField!
@IBOutlet weak var PasswordTextField: UITextField!

// Do any additional setup after loading the view.
override func viewDidLoad() {
    super.viewDidLoad()

    EmailAddressTextField.delegate = self
    PasswordTextField.delegate = self
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
}

@IBAction func LogInButton(_ sender: Any) {
    if (EmailAddressTextField.text != "" && PasswordTextField.text != ""){
        Auth.auth().signIn(withEmail: EmailAddressTextField.text!, password: PasswordTextField.text!) { user, error in
            if error == nil {
                self.performSegue(withIdentifier: "LogInSegue", sender: nil)
            } else {
//                    let alert = UIAlertController(title: "Error", message: "Enter a correct email and password", preferredStyle: .alert)
//                    let action = UIAlertAction(title: "OK", style: .default, handler: nil)
//                    alert.addAction(action)
//                    self.present(alert, animated: true, completion: nil)

                //use like this...
                self.showAlert(title: "Error", msg: "Enter a correct email and password", actions: nil)
            }

        }
    }
}

//###############################################
func showAlert(title: String, msg: String, actions:[UIAlertAction]?) {

    var actions = actions
    let alertVC = UIAlertController(title: title, message: msg, preferredStyle: .alert)

    if actions == nil {
        actions = [UIAlertAction(title: "OK", style: .default, handler: nil)]
    }

    for action in actions! {
        alertVC.addAction(action)
    }

    if let rootVC = UIApplication.shared.delegate?.window??.rootViewController {
        rootVC.present(alertVC, animated: true, completion: nil)
    } else {
        print("Root view controller is not set.")
    }
}
//###############################################

}

Answer 3

在主要活动中展示它：

dispatch_async(dispatch_get_main_queue(), ^{
   let alert = UIAlertController(title: "Error", message: "Enter a correct email and password", preferredStyle: .alert)
   let action = UIAlertAction(title: "OK", style: .default, handler: nil)
   alert.addAction(action)
   self.present(alert, animated: true, completion: nil)
});