CODEWITHSUNDEEP
iosobjective-cuialertcontrollerpresentviewcontroller
iBug
iBug

Reputation: 2352

UIAlertController crash for being presented in backgroundThread objective C

I have been using UIAlertController in previous apps but I am facing a strange error this time. Here is my code which I using to present it:

     UIAlertController *alertController = [UIAlertController alertControllerWithTitle:ALERT_TITLE_STRING message:message preferredStyle:UIAlertControllerStyleAlert];
     [alertController addAction:[UIAlertAction actionWithTitle:OK_STRING style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

     }]];
     [[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:^{

     }];

Everything was fine but now I my app crashes on last line. Here is error:

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.

I am not using autolayout in my app. I have no idea why I am getting this error.

Any clues?

Upvotes: 3

Views: 3402

Answers (3)

Gil Sand
Gil Sand

Reputation: 6038

You can't handle UI in any other thread than the main thread.

If you're currently in another thread, you can force a block of code to be executed on the main thread anyway, by putting it inside the following block.

dispatch_async(dispatch_get_main_queue(), ^{
        //Display your UIAlertController here
    });

Upvotes: 6

Roberto Ferraz
Roberto Ferraz

Reputation: 2521

This error is displayed when you try to do UI tasks in a background thread. Just change your code to this:

dispatch_async(dispatch_get_main_queue(), ^{

        UIAlertController *alertController = [UIAlertController alertControllerWithTitle:ALERT_TITLE_STRING message:message preferredStyle:UIAlertControllerStyleAlert];
     [alertController addAction:[UIAlertAction actionWithTitle:OK_STRING style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {

     }]];


        [[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:^{
     }];
    });

Upvotes: 9

jrturton
jrturton

Reputation: 119272

You're not allowed to perform UI operations on any thread but the main thread. The alert controller will be using autolayout internally which is why you're seeing the error.

Use dispatch_asyncto present the alert from the main thread instead.

Upvotes: 2

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