警报不会关闭（警告：尝试从视图控制器关闭...）

Question

So I have a function that shows an alert while Alamofire is doing some stuff and I want to dismiss the alert when Alamofire is done but sometimes it works and sometimes it doesn't! and when it doesn't work I'm getting the error ( iOS 13, Xcode 11 Beta 5 ): Warning: Attempt to dismiss from view controller (UITabBarController: 0x7f90b7013a00) while a presentation or dismiss is in progress!

This is the function I use to show the alert:

func showLoadingDialog(show : Bool)  {
        let alert = UIAlertController(title: nil, message: "⏳ Please wait...", preferredStyle: .alert)
        if show == true {


            let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
            loadingIndicator.hidesWhenStopped = true
            loadingIndicator.style = .medium
            loadingIndicator.startAnimating()
            alert.view.addSubview(loadingIndicator)
            present(alert, animated: true, completion: nil)
        } else {
            dismiss(animated: true, completion: nil)
            // I've tried the "alert.dismiss" but it doesn't work!
            //alert.dismiss(animated: true, completion: nil)
            alert.removeFromParent()
        }
    }

Also I'm using tab bars and inside one of the tab bars I'm using the navigation controller and inside that I've a tableview so when the user clicks the cells it goes to another view controller (inside the same storyboard file) using this code:

let detailsVC = storyboard?.instantiateViewController(identifier: "Bdetails") as? DetailsController
    self.navigationController?.pushViewController(detailsVC!, animated: true)

and then I've also disabled the navigation bar (the header I guess and I'm using a custom button to return to the previews page using this code:

self.navigationController?.popViewController(animated: true)

also here is the Alamofire where I've put the alert function and I'm using it inside viewDidLoad:

func libHttp(url: String) {

    // Showing the alert.
    showLoadingDialog(show: true)
        Alamofire.request(url).responseJSON { (responseData) ->
            Void in
            if ((responseData.result.value) != nil) {

                let libJSON = JSON(responseData.result.value!)
                if let libData = libJSON.array {
                    for detail in libData {
                        // putting the values into an object from a custom class
                    }

                    // Updates the storyboard elements' value with the objects values.
                    self.update()

                    // dismissing the alert.
                    self.showLoadingDialog(show: false)
                }
            }
        }
    }

Answer 1

This seems like a race condition involving when you call your libHttp(url:) function. Check for scenarios where you are dismissing the alert after you pop the viewController from the navigation controller.

Answer 2

Your showLoadingDialog(show : Bool) looks a little strange. When passing true to it, to display the alert, everything seems to be setup correctly, but when passing false, to hide the alert, you are creating a new UIAlertController , never actually present it, and then tries to remove it. I'm guessing that you really don't want to create a new UIAlertController here, but would instead like to remove an already presented UIAlertController ?

Maybe you can do something like this instead?

func showLoadingDialog() -> UIAlertController  {
    let alert = UIAlertController(title: nil, message: "⏳ Please wait...", preferredStyle: .alert)
    let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
    loadingIndicator.hidesWhenStopped = true
    loadingIndicator.style = .medium
    loadingIndicator.startAnimating()
    alert.view.addSubview(loadingIndicator)
    present(alert, animated: true, completion: nil)
    return alert
}

func libHttp(url: String) {

    // Showing the alert.
    let alert = showLoadingDialog()
    Alamofire.request(url).responseJSON { (responseData) ->
        Void in
        if ((responseData.result.value) != nil) {

            let libJSON = JSON(responseData.result.value!)
            if let libData = libJSON.array {
                for detail in libData {
                    // putting the values into an object from a custom class
                }

                // Updates the storyboard elements' value with the objects values.
                self.update()

                // dismissing the alert.
                alert.dismiss(animated: true, completion: nil)
            }
        }
    }
}

Answer 3

Your alert.dismiss call isn't working because you instanciate a new AlertController each time you call the showLoadingDialog .

Here is a minimum viable working example:

import UIKit

class ViewController: UIViewController {
    let alert = UIAlertController(title: nil, message: "⏳ Please wait...", preferredStyle: .alert)

    func showLoadingDialog(show : Bool) {
        if show {
            let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
            loadingIndicator.hidesWhenStopped = true
            loadingIndicator.style = .medium
            loadingIndicator.startAnimating()
            alert.view.addSubview(loadingIndicator)
            present(alert, animated: true, completion: nil)
        } else {
            alert.dismiss(animated: true, completion: nil)
        }
    }

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

        showLoadingDialog(show: true)

        DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
            self.showLoadingDialog(show: false)
        }
    }
}

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