xcode - pageViewController setViewControllers crashes with "Invalid parameter not satisfying: [views count] == 3"

Question

I know that there are several other questions like this, but i couldn't find a solution for my problem. I use a pageViewController which displays different ViewControllers. Every time the pageViewController moves forward I check the input of the lastPage. If it's wrong the pageViewController should go back to that page by using the setViewController method. Without this method everything works fine but if I try to use it the app crashes with the following exception:

19:48:25.596 Phook[23579:60b] *** Assertion failure in -[_UIQueuingScrollView _replaceViews:updatingContents:adjustContentInsets:animated:], /SourceCache/UIKit_Sim/UIKit-2935.137/_UIQueuingScrollView.m:383  
2014-06-02 19:48:25.600 Phook[23579:60b] *** Terminating app due to uncaught   exception 'NSInternalInconsistencyException', reason: 'Invalid parameter not satisfying:   [views count] == 3'

And here's my code:

- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished
   previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed
{
    if (completed && finished)
    {

        RegisterUserPageContent* lastPage = (RegisterUserPageContent*)previousViewControllers[ previousViewControllers.count-1];
        int lastIndex   = lastPage.pageIndex;
        int newIndex    = ((RegisterUserPageContent*)[self.pageViewController.viewControllers objectAtIndex:0]).pageIndex;

        if (newIndex > lastIndex)
        {   // Moved Forward
            if(!lastPage.testInput)
            {
                [self.pageViewController setViewControllers:@[ [self.storyboard instantiateViewControllerWithIdentifier:_pageStoryBoardIDs[0]] ]
                                         direction:UIPageViewControllerNavigationDirectionReverse
                                         animated:YES completion:nil];


            }
        }
        else
        {   // Moved Reverse

        }
    }
}

As I already said. I searched a lot and implemented some solutions but nothing helped. Thanks.

question from:https://stackoverflow.com/questions/24000712/pageviewcontroller-setviewcontrollers-crashes-with-invalid-parameter-not-satisf

Answer 1

I ran into the same problem, and was able to solve it using a tip from this answer https://stackoverflow.com/a/20973822/3757370. Simply placing the setViewControllers:direction:animated:completion: code inside of a dispatch_async block on the main queue fixed it for me. For you this would look like

dispatch_async(dispatch_get_main_queue(), ^{
    [self.pageViewController setViewControllers:@[ [self.storyboard instantiateViewControllerWithIdentifier:_pageStoryBoardIDs[0]] ]
                                     direction:UIPageViewControllerNavigationDirectionReverse
                                     animated:YES completion:nil];
});

Hope it helps!