autolayout - iOS 8 UIPageViewController Applying Constraints After Transitions

Question

My app has a multi-pane tutorial-style view that users swipe through to learn about the app. This is implemented very much as described in this tutorial. Having implemented it for both iOS 7 and 8, I'm comparing how they work, and finding issues with the latter — I'm running Xcode 6 GM here.

It seems that the UIPageViewController is rendering the views after the transition is complete. I overrode the delegate methods to see what was going on:

- (void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers
{
   NSLog(@"Frame size before: %@", NSStringFromCGRect([(UIViewController*)pendingViewControllers[0] view].frame));
}

- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed
{
   NSLog(@"Frame size after: %@", NSStringFromCGRect([(UIViewController*)previousViewControllers[0] view].frame));
}

And here's a sample output:

Frame size before: {{0, 0}, {600, 600}}
Frame size after: {{0, 0}, {320, 568}}

This manifests like so: swipe to the left to pull in the next view, and note a 32-pt white space at the bottom of the new view. Once the transition is complete, it jerks into its proper layout.

Is this a bug in iOS 8, perhaps? I'm all out of guesses at this point.

Answer 1

I figured out you need to base your constraints on the view and not the layout guide of your view controller. This will ensure your view controller respects the constraints you set prior to the transition in a PageViewController.

you can do this like so:

Remember to uncheck "Constrain to margins"