Error when dismissing view controller

Getting an error when dismissing a view controller, not seen anything like it before, and not much about it on the internet.

heres the error: * Assertion failure in -[UIKeyboardTaskQueue waitUntilAllTasksAreFinished], /SourceCache/UIKit/UIKit-2903.2/Keyboard/UIKeyboardTaskQueue.m:368

a bit of background, i dismiss the view controller after saving some data. the data saves successfully, every time. also, i recently changed the date saving code to run on the main thread for this one method, as i was having some issues saving in the background.

any ideas why this is happening?

Thanks in advance.

Answers


I recieved this error when I was calling -presentViewController:animated:completion: on a thread that was not the main thread (from a callback in a network request). The solution is to dispatch your calls to present and dismiss view controllers to the main thread:

dispatch_async(dispatch_get_main_queue(), ^{
    //Code that presents or dismisses a view controller here
});

I had the same problem while calling the camera view

Swift syntax for the same problem:

dispatch_async(dispatch_get_main_queue(), { 
    //Code that presents or dismisses a view controller here  
    self.presentViewController(imagePicker, animated: true, completion: nil)
})

Make sure to dismiss the view controller from the presenting view.

https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/ModalViewControllers/ModalViewControllers.html

When it comes time to dismiss a presented view controller, the preferred approach is to let the presenting view controller dismiss it. In other words, whenever possible, the same view controller that presented the view controller should also take responsibility for dismissing it.


In the target view controller define delegate and protocol:

@class TargetVC;
@protocol TargetVCDelegate <NSObject>
-(void)dismissTargetVC:(TargetVC*)vc;
@end

@interface TargetVC : UIViewController
@property (nonatomic, weak) id<TargetVCDelegate> delegate;
@end

when you done the job at the target view controller call the delegate:
if( [self.delegate respondsToSelector:@selector(dismissTargetVC:)])
{
   [self.delegate dismissTargetVC:self];
}

The implementation of the delegate protocol should be:
-(void)dismissTargetVC:(TargetVC*)vc
{
    [vc dismissViewControllerAnimated:YES completion:nil];

    // you can get relevant data from vc as you still hold reference to it in this block

    // your code ...
}

You must make sure not only that present/dissmissViewController called on main thread but also you have to make sure that present/dismissViewController is called from the same parent viewController.

For example there are two navigationController children. First child view controller presents the second child for some job that will return thru a delegate (interface). After the job is done second child dismisses itself and calls to delegate(interface) function with have to present another viweController (for example customPopup) -> that's rises the error since the second child view controller is not dismissed when the present of popup called, but already demised when the dismiss of popup called.

So in this case:

  dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(400 * NSEC_PER_MSEC)), dispatch_get_main_queue(), { () -> Void in
            if let fs = self.scenarios[indexPath.item]{
                fs.loadScenario()
                sDelegate.onSelectedScenario(fs)
            }
        })

will do.


If someone is having Assertion Failure issue then here is the solution for Swift 3:

OperationQueue.main.addOperation{
    <your segue or function call>
}

Tested On: Xcode 8.3.2 and Swift 3.1


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