Alert Controller Freezes on main thread

Question

Am connecting to the services and receiving the data from backend. The code is as follows:

 _ = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) in

        if response != nil{

           var responseREcvd = response as? NSHTTPURLResponse
            if responseREcvd?.statusCode == 404 {
                let  alertControler = UIAlertController(title: "404", message: "Server Down.", preferredStyle: .Alert)
                let alertAction = UIAlertAction(title: "OK", style: .Default, handler: nil)
                alertControler.addAction(alertAction)
                dispatch_async(dispatch_get_main_queue(), {
                    targetVC.presentViewController(alertControler, animated: true, completion: nil)
                })
            }
        }

The alert is displayed but it freezes the UI. When I press the OK action button, no action is invoked.

@USER_NAME yes the issue is fixed. The issue was there was one more instance of a uiview that was hiding on the screen. I had to remove it to be able to press the OK button of the alert controller. — Prabhakar Patil, Jun 13 '17 at 04:35

Jitendra Modi · Answer 1 · 2016-12-16T13:36:46.720

0

Try this extension

  extension UIAlertController {

    func show() {
        present(true, completion: nil)
    }

    func present(
        animated: Bool, completion: (() -> Void)?) {
        if let rootVC = UIApplication.sharedApplication().keyWindow?.rootViewController {
            presentFromController(rootVC, animated: animated, completion: completion)
        }
    }

    private func presentFromController(controller: UIViewController, animated: Bool, completion: (() -> Void)?) {
        self.addAction(UIAlertAction.init(title: "Ok", style: .Default, handler: { (true) in
            self.dismissViewControllerAnimated(true, completion: nil)
        }))
        if let navVC = controller as? UINavigationController,
            let visibleVC = navVC.visibleViewController {
            presentFromController(visibleVC, animated: animated, completion: completion)
        } else
            if let tabVC = controller as? UITabBarController,
                let selectedVC = tabVC.selectedViewController {
                presentFromController(selectedVC, animated: animated, completion: completion)
            } else {
                controller.presentViewController(self, animated: animated, completion: completion);
        }
    }
}

USE:

let alertController = UIAlertController(title: "At \((arr_day.objectAtIndex(index.row - 1) as! String)) End Time Missing", message: "", preferredStyle: .Alert)
alertController.show()

Hope this will work for you

edited Dec 16 '16 at 13:36

answered Dec 16 '16 at 13:09

Jitendra Modi

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The UI freezes. No Touch are recognised. I tried your solution but no luck. – Prabhakar Patil Dec 16 '16 at 13:16
@PrabhakarPatil If you want I can give you extension I used for alertviewController ? then U have to just call that extension for displaying alert. And why did you present alertviewcontroller into dispatch ? – Jitendra Modi Dec 16 '16 at 13:23
Thanks for the efforts , but still no luck. The UI freezes completely. – Prabhakar Patil Dec 16 '16 at 13:39
@PrabhakarPatil why did you put present alertcontroller into dispatch ? – Jitendra Modi Dec 16 '16 at 13:40
am calling dataTaskWithRequest, which is executed on the background thread. So when we try to present the alert controller it throws an error, asking you to move the control to the main thread. Hence, we have to put the present alertController in dispatch black. – Prabhakar Patil Dec 16 '16 at 13:48
any other solutions? – Prabhakar Patil Dec 16 '16 at 13:57
@PrabhakarPatil Will you share your project, if you dont mind ? I will check it and then let you know about your problem – Jitendra Modi Dec 19 '16 at 06:14
change preferred style .alert to .actionSheet somehow it work.... i still search for WHY! – Muhammad Asyraf Mar 09 '20 at 08:01

score -1 · Answer 2 · answered Feb 07 '17 at 12:51

try to use NSOperationQueue:

 _ = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) in

    if response != nil{

       var responseREcvd = response as? NSHTTPURLResponse
        if responseREcvd?.statusCode == 404 {
            let  alertControler = UIAlertController(title: "404", message: "Server Down.", preferredStyle: .Alert)
            let alertAction = UIAlertAction(title: "OK", style: .Default, handler: nil)
            alertControler.addAction(alertAction)
            dispatch_async(dispatch_get_main_queue(), {NSOperationQueue.mainQueue().addOperationWithBlock {
                targetVC.presentViewController(alertControler, animated: true, completion: nil)}
            })
        }
    }

In other words you suggest to call dispatch_async { dispatch_async { ... } } which is incorrect in most cases — Vyachaslav Gerchicov, Oct 04 '21 at 09:19

Alert Controller Freezes on main thread

2 Answers2