Open Radar

 
Summary:
I would like to display UIAlertController after document picker dismissed. However currently there is no way to coordinate that. It would be really helpful to have a delegate method to be notified that picker dismissed or move didPickDocumentAtURL to the point when controller already dismissed.

Steps to Reproduce:

1. Present UIDocumentPickerViewController
2. Present UIAlertController from didPickDocumentAtURL

Expected Results:
UIAlertController presented from parent controller.

Actual Results:
UIAlertController does not even show up and I receive a warning in console:

Warning: Attempt to present <UIAlertController: 0x19084a50> on <MYViewController: 0x190a08f0> whose view is not in the window hierarchy!

Regression:

Notes:
Currently I skip one run loop to hook up transitionCoordinator.

- (void)documentPicker:(UIDocumentPickerViewController *)controller didPickDocumentAtURL:(NSURL *)url {
    dispatch_async(dispatch_get_main_queue(), ^{
        NSAssert(controller.transitionCoordinator, @"UIDocumentPickerViewController does not have transitionCoordinator?");
        
        [controller.transitionCoordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext> context) {
            
        } completion:^(id<UIViewControllerTransitionCoordinatorContext> context) {
            [self _showAlertController];
        }];
    });
}