Performing a Segue Inside of a Completion Handler

Question

I'm attempting to perform a storyboard segue inside of a completion handler like so:

movieWriter.finishRecordingWithCompletionHandler({ () -> Void in
            //Leave this view
            self.performSegueWithIdentifier("decisionSegue", sender: self)
        })

and getting the following warning:

This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.

The completion handler is running on a background so I understand why I'm getting this error, my question is what are my options for performing this segue without getting this error?

The reason I'm performing the segue in the completion handler is that the completion handler is called after a recorded movie is done being written to file and the view being segued to plays the movie, hence it needs to be on file before segueing.

I think its easy to google .90 % of the questions are already answered perfectly . — Muhammad Adnan, Dec 16 '15 at 06:57

score 4 · Answer 1 · edited May 23 '17 at 10:27

4

Put it in dispatch queue :

dispatch_async(dispatch_get_main_queue(),{
    self.performSegueWithIdentifier("decisionSegue", sender: self)
})

Hope it will work

For more detailed information : This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes

edited May 23 '17 at 10:27

Community

1
1

answered Dec 16 '15 at 06:49

Ashish Kakkad

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score 4 · Accepted Answer · answered Dec 16 '15 at 07:01

Whenever your perform any operation on UI/active view then it has to be on main thread and not background thread.

Do as following:

__weak typeof(self) weakSelf = self; //Best practice
                                     //Provide a weak reference in block and not strong.

movieWriter.finishRecordingWithCompletionHandler({ () -> Void in

     dispatch_async(dispatch_get_main_queue(),{

        weakSelf.performSegueWithIdentifier("decisionSegue", sender:weakSelf)

     })            
})

All answers helped, so thank you everyone, but you used swift, the code I provided, and recommended using weak self so this answer helped me the most. Thanks! — tnev, Dec 17 '15 at 00:59

Muhammad Waqas Bhati · Answer 3 · 2019-04-03T05:32:33.593

This Error is telling that You are performing some UI update task from Background Thread and it's not possible to Update UI from background thread so you have to access main Thread and then perform segue.

Objective-C:

dispatch_async(dispatch_get_main_queue(), ^{
    // update some UI
    // Perform your Segue here
});

Swift:

DispatchQueue.main.async {
    // update some UI
    // Perform your Segue here    
}

Hope it will help you.

Performing a Segue Inside of a Completion Handler

3 Answers3