How To Fix Warning Attempt To Present UIAlertController On ViewController Whose View Is Not In The Window Hierarchy

I want to implement an effect that when the iOS app starts, it popup an alert dialog on the screen and displays some messages. But during the process, I meet an error message like below, and the alert dialog is not displayed as I want. This article will tell you how to fix this issue.

1. Error Message.

  1. Below is the error message.
    TestProject[2673:43682] Warning: Attempt to present <UIAlertController: 0x7f8ae603c000> on <TestProject.ViewController: 0x7f8ae5d097d0> whose view is not in the window hierarchy!

2. How To Fix Above Error.

  1. The reason for this error is because I create the instance of the swift UIAlertController class in the ViewController class’s viewDidLoad() method.
  2. To fix this error, I need to override ViewController class’s viewDidAppear method and put the UIAlertController class initialization code in the viewDidAppear method like below.
  3. ViewController.swift
    //
    //  ViewController.swift
    //  TestProject
    //
    //  Copyright © 2019 dev2qa.com. All rights reserved.
    //
    
    import UIKit
    
    class ViewController: UIViewController {
        
        var message:String = ""
    
        override func viewDidLoad() {
            super.viewDidLoad()
            
            message = "Hello Swift"
    
            print(message)
                
        }
        
        /* Override the viewDidAppear method and display iOS swift alert popup dialog in it. */
        override func viewDidAppear(_ animated: Bool) {
    
            /* Below method will display a swift alert dialog window. */
            presentAlertDialog()
        }
        
        /* Below function will create an iOS swift alert dialog and display the message in it. */
        func presentAlertDialog() -> Void{
    
            /* Create a UIAlertController object with provided title, message and alert dialog style. */
            let alertController:UIAlertController = UIAlertController(title: "Message", message: message, preferredStyle: UIAlertController.Style.alert)
    
         
            /* Create a UIAlertAction object with title to implement the alert dialog OK button. */    
            let alertAction:UIAlertAction = UIAlertAction(title: "OK", style: UIAlertAction.Style.default, handler:nil)
            /* Add above UIAlertAction button to the UIAlertController object. */        
            alertController.addAction(alertAction)
            
    
            /* Display the swift alert dialog window. */
            present(alertController, animated: true, completion: nil)
        }
    
    
    }
  4. Below is the screen when executing the above app.
    popup-an-alert-dialog-when-ios-swift-app-start

Reference

  1. How To Prompt Alert Dialog When Click A Button In Swift
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