Attempt to present UIAlertController on View Contr

问题:

I have an alert view that I am trying to present on a photo view.

The photos are displayed in a list and can be pushed to a full-screen view.

The photo view is being displayed programmatically. I think that is what is causing the issue because the alert view is trying to present another view, on top of the (photo) view that's already presented.

The alert view is trying to display, but getting this error:

Warning: Attempt to present <UIAlertController: 0x147d2c6b0>  on <LiveDeadApp.ListViewController: 0x147d614c0> which is already presenting (null)

The line that might be in question is this one:

 self.present(textPrompt, animated: true, completion: nil)

This is the main list view

This is the main list view when a screenshot is taken

This is the main photo view

This is the popover in the main photo view (accessed via the "i" button)

When a screenshot is taken on the main photo view, no alert view occurs. However, when the device's orientation is changed, the photo view goes back to the list and shows the alert.

This is what I am trying to do:

Swift 3 in iOS 10

Thank you!

Here is the list view and photo view's code:

import UIKit
import Kingfisher
import SKPhotoBrowser

class ListViewCell: UITableViewCell {

@IBOutlet weak var Cellimage: UIImageView!

@IBOutlet weak var cellVenue: UILabel!

@IBOutlet weak var cellLocation: UILabel!

@IBOutlet weak var cellDate: UILabel!
@IBOutlet weak var aiView: UIActivityIndicatorView!
}

class ListViewController: UITableViewController {

var subcategory:Subcategory!

var objects:[[String:String]] = [[String:String]]()

var images = [SKPhotoProtocol]()



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


}

override func viewDidLoad() {
    super.viewDidLoad()


    self.tableView.separatorStyle = .none

    self.view.backgroundColor = UIColor.black

    self.navigationController?.navigationBar.titleTextAttributes = [NSForegroundColorAttributeName: UIColor.white]

    navigationController!.navigationBar.barTintColor = UIColor.black

    let requireTextInput = "require text input"
    // add observer for screen shot
    NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationUserDidTakeScreenshot, object: nil, queue: OperationQueue.main, using:
        { notification in

            self.definesPresentationContext = true

            var inputTextField = UITextField()

            let textPrompt = UIAlertController(title: "Test!", message: "Testing!", preferredStyle: .alert)

            textPrompt.addAction(UIAlertAction(title: "Continue", style: .default, handler: {
                (action) -> Void in
                // if the input match the required text

                let str = inputTextField.text
                if str == requireTextInput {
                    print("right")
                } else {
                    print("wrong")
                }

            }))

            textPrompt.addTextField(configurationHandler: {(textField: UITextField!) in
                textField.placeholder = ""
                inputTextField = textField

            })

            self.present(textPrompt, animated: true, completion: nil)

    })

    if subcategory != nil {
        self.title = subcategory.title
        self.objects = subcategory.photos

        createLocalPhotos()

        self.tableView.reloadData()
    }


}

func createLocalPhotos() {

    for item in objects {
        let photo = SKPhoto.photoWithImageURL(item["url"]!)
        photo.shouldCachePhotoURLImage = true
        images.append(photo)
    }

}

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

override func numberOfSections(in tableView: UITableView) -> Int {
    return 1
}

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return objects.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    let cell: ListViewCell = tableView.dequeueReusableCell(withIdentifier: "Cell") as! ListViewCell

    let item = objects[indexPath.row]

    let title = item["title"]
    let location = item["location"]
    let date = item["date"]
    let urlSrt = item["url"]


    cell.cellVenue.text = title
    cell.cellLocation.text = location
    cell.cellDate.text = date

    if let url = URL(string: urlSrt!) {
        cell.aiView.startAnimating()
        cell.Cellimage.kf.setImage(with: url, placeholder: nil, options: nil, progressBlock: nil, completionHandler: { (image, error, cacheType, url) in
            cell.aiView.stopAnimating()
        })
    }

    return cell

}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    let cell = tableView.cellForRow(at: indexPath) as! ListViewCell

    if(cell.Cellimage.image != nil ) {
        SKPhotoBrowserOptions.displayToolbar = false
        SKPhotoBrowserOptions.displayCounterLabel = false
        SKPhotoBrowserOptions.displayBackAndForwardButton = false
        SKPhotoBrowserOptions.displayAction = false
        SKPhotoBrowserOptions.displayDeleteButton = true
        SKPhotoBrowserOptions.displayHorizontalScrollIndicator = false
        SKPhotoBrowserOptions.displayVerticalScrollIndicator = false
        SKPhotoBrowserOptions.displayStatusbar = false
        SKPhotoBrowserOptions.disableVerticalSwipe = true
        SKPhotoBrowserOptions.bounceAnimation = false
        let browser = ExtendedSKPhotoBrowser(originImage: cell.Cellimage.image!, photos: images, animatedFromView: cell)

        let btnSize = 80//24 * UIScreen.main.scale

        browser.updateCloseButton(UIImage(named: "ic_close_white")!, size: CGSize(width: btnSize, height: btnSize))
        browser.updateDeleteButton(UIImage(named: "ic_info_white")!, size: CGSize(width: btnSize, height: btnSize))
        browser.initializePageIndex(indexPath.row)
        browser.delegate = self
        present(browser, animated: true, completion: {})
        browser.toggleControls()
    }
}

override var prefersStatusBarHidden: Bool {
    get {
        return true
    }
}


var popOverVC:PopUpViewController!
}

extension ListViewController: SKPhotoBrowserDelegate {
func didShowPhotoAtIndex(_ index: Int) {






}

func willDismissAtPageIndex(_ index: Int) {

}

private func willShowActionSheet(photoIndex: Int) {
    // do some handle if you need
}

func didDismissAtPageIndex(_ index: Int) {
}

func didDismissActionSheetWithButtonIndex(_ buttonIndex: Int, photoIndex: Int) {
    // handle dismissing custom actions
}

func removePhoto(_ browser: SKPhotoBrowser, index: Int, reload: (() -> Void)) {
    popOverVC = self.storyboard?.instantiateViewController(withIdentifier: "sbPopUpID") as! PopUpViewController
    popOverVC.photoData = objects[index]

}

func viewForPhoto(_ browser: SKPhotoBrowser, index: Int) -> UIView? {
    return tableView.cellForRow(at: IndexPath(row: index, section: 0))
}
}


open class ExtendedSKPhotoBrowser: SKPhotoBrowser {

open override var preferredStatusBarStyle: UIStatusBarStyle {
    return .lightContent // white statusbar, .default is black
}

open override var prefersStatusBarHidden: Bool {
    return true
}
}

回答1:

The problem is really simple, you are trying to display another UIAlertController on the currently presented UIAlertController.

So, how to solve such a case?

1. You need to get a list of all UIAlertController's you use in your current view controller.

2. You have to check the logic for displaying alerts in your current view controller (or other view controllers if you are doing async requests).

3. Your code must be like this when you want to display one alert on top of another.

Assume loadingAlert is currently displaying on the screen:

self.loadingAlert.dismiss(animated: true, completion: {
     let anotherAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
     let okAction = UIAlertAction(title: "OK", style: .default, handler: nil)
     anotherAlert.addAction(okAction)
     self.present(anotherAlert, animated: true, completion: nil)
})

You have to dismiss the first one before the next one can appear. I made this answer for dismissing an alert without buttons on it to make it more efficient.

So, what about the alert with action buttons?

It will dismiss automatically when you click one of the action buttons on UIAlertController that you created.

But, if you are displaying two UIAlertControllers which include UIButtons at the same time, the problem will still occur. You need to re-check the logic for each, or you can handle it in the handler for each action :

self.connectionErrorAlert.dismiss(animated: true, completion: {
     let anotherAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
     let okAction = UIAlertAction(title: "OK", style: .default, handler: {action in
            let nextAlert = UIAlertController(title: "New One", message: "The Previous one is dismissed", preferredStyle: .alert)
            self.present(nextAlert, animated: true, completion: nil)
     })
     anotherAlert.addAction(okAction)
     self.present(anotherAlert, animated: true, completion: nil)
})

For an Answer to Mike :

DispatchQueue.main.async(execute: {

      if self.presentedViewController == nil {
           print("Alert comes up with the intended ViewController")
           var inputTextField = UITextField()

           let textPrompt = UIAlertController(title: "Test", message: "Testing", preferredStyle: .alert)

           textPrompt.addAction(UIAlertAction(title: "Continue", style: .default, handler: {
               (action) -> Void in
               // if the input matches the required text

               let str = inputTextField.text
               if str == requireTextInput {
                    print("right")
               } else {
                    print("wrong")
               }

           }))

           textPrompt.addTextField(configurationHandler: {(textField: UITextField!) in
                textField.placeholder = ""
                inputTextField = textField

            })
            weakSelf?.present(textPrompt, animated: true, completion: nil)
      } else {
            // either the Alert is already presented, or any other view controller
            // is active (e.g. a PopOver)
            // ...
            let thePresentedVC : UIViewController? = self.presentedViewController as UIViewController?
            if thePresentedVC != nil {
                 if let _ : UIAlertController = thePresentedVC as? UIAlertController {
                      print("Alert not necessary, already on the screen !")

              } else {

                      print("Alert comes up via another presented VC, e.g. a PopOver")
              }
            }
       }
})

Thanks to @Luke Answer : https://stackoverflow.com/a/30741496/3378606

回答2:

in ViewDidLoad,
Make weak variable, like weak var weakSelf = self

in NotificationCenter,
present textPropmt like

weak var weakSelf = self
NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationUserDidTakeScreenshot, object: nil, queue: OperationQueue.main, using:
        { notification in
 DispatchQueue.main.async(execute: {
  //create textPrompt here in Main Thread
  weakSelf.present(textPrompt, animated: true, completion: nil)
 })
})

回答3:

Duplicated from my answer here

In my situation, I was not able to put mine in a class override. So, here is what I got:

let viewController = self // I had viewController passed in as a function,
                          // but otherwise you can do this


// Present the view controller
let currentViewController = UIApplication.shared.keyWindow?.rootViewController
currentViewController?.dismiss(animated: true, completion: nil)

if viewController.presentedViewController == nil {
    currentViewController?.present(alert, animated: true, completion: nil)
} else {
    viewController.present(alert, animated: true, completion: nil)
}

回答4:

I've suffered with this problem and tracked it down to this. Here is a simple app with two buttons on it. Tapping the first button causes the "2019-03-05 16:58:04.094541-0500 ReadJason[41100:1610082] Warning: Attempt to present on which is already presenting " error.

The issue was caused by copying button 2 to make button 1. Each button is tied to an action (btn1, and btn2). When I copied btn2 to make btn1, the tie to btn2 was included in the code of btn1. I then added the tie to btn1 and this resulted in two send events being tied to btn1 - and this is what causes the error.

Inspecting the events to button 1 reveals the two actions:screen shot showing the two actions. Removing the unwanted action clears the error.

screen shot of main.storyboard

<pre><code>    
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIButton *btn1;
@property (weak, nonatomic) IBOutlet UIButton *btn2;
@end

@implementation ViewController

- (void)viewDidLoad {
   [super viewDidLoad];
}

- (IBAction)btn1:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn1"
                   message:@"This is Btn1." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}

- (IBAction)btn2:(id)sender {
   UIAlertController *alert = [UIAlertController alertControllerWithTitle:@"Btn2"
                     message:@"This is Btn2." preferredStyle:UIAlertControllerStyleAlert];

   UIAlertAction* defaultAction = [UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * action) {}];

   [alert addAction:defaultAction];
   [self presentViewController:alert animated:YES completion:nil];
}
</code></pre>

回答5:

Hy, I tried a more simple solution that seems to work, and is able to present a second alert in front of the first, that will stay (no need to dismiss before user answers the question) :

if self.presentedViewController==nil{
    self.present(MyAlert, animated: true, completion: nil)
}else{
    self.presentedViewController!.present(MyAlert, animated: true, completion: nil)
}

回答6:

I believe, you need to make sure if there is already another AlerViewController trying to represent itself on the ViewController.

At least that was my problem.