objective c - Issue with Auto Layout on iOS 8 (code works perfectly on iOS 7)

Question

I have an app that was built using auto-layout and everything still works as expected when I run it on my iOS 7 device, however when I run it on an iOS 8 device some of my constraints go a little wacky.

I actually experienced a similar issue in another app but it wasn't a big issue. Now, I'm starting to wonder if it is a bug in the iOS 8 SDK or if there is a new way of handling auto layout in iOS8 that I'm not aware of.

Here is my setup: I have a UIView with a UIImageView embedded inside it. Both the view and the image view have constraints pinning their bottom, leading & trailing edges to their superviews with constant = 0.

The UIView also has its top edge pinned to its superview and I have an IBOutlet connected to the constraint in order to adjust it programatically. The UIImageView has a fourth constraint fixing its height to the height of the device (in my case 568).

Here is the behavior I am expecting/achieving in iOS 7: I am trying to shrink the height of the container view and cause the top of the image view to be cut off w/o the aspect ratio changing (sort of looks like you cropped the top of the image off)...this is why I have pinned the height of the image view and the bottom edge.

What actually happens in iOS8: The container view shrinks as expected (it stays pinned to the sides & bottom & the height shrinks). The UIImageView behaves as if it had a top space constraint with cosntant == 0. Instead of cutting off the top of the image, the whole image shrinks down. Since I have the image in AspectFit mode, the sides pinch in as well to keep the aspect ratio the same (but the imageView itself remains pinned to the leading, trailing & bottom edges as it should).

How I do it: I have a notification that fires from another part of my code to adjust the top-space constraint hooked up to the IBOutlet. The method it calls is really quite simple:

- (void) setTopSpaceForContainerView:(NSNotification*) notif{
    containerView_TopSpace.constant = [[notif.userInfo objectForKey:kTopSpace] intValue];
    [self.view setNeedsUpdateConstraints];
    [self.view setNeedsLayout];
}

Anyone else have a similar experience? I'm trying to find a workaround, but iOS 8 just seems determined to shrink my image.

Thanks a ton!

Answer 1

This is definitely an iOS 8 bug. I was able to work around it by sending setNeedsLayout to the container view (the superview of the image view).

I see that you're sending setNeedsLayout to self.view. If that code is in your view controller, then I guess self.view is not the container view. Try sending setNeedsLayout to the container view directly.

Demo project is here.