UIScrollView wrong offset with Auto Layout

Question

I have a fairly simple view configuration: A `UIViewController`, with a child `UIScrollView` and a `UIImageView` in this `UIScrollView`. I set the `UIImageView` with a height sufficient to break out of the visible area (ie. higher to `1024pt`), and set the `Bottom space to superview` constraint of my `UIImageView` to a fixed positive value (`20` for example). The whole setup works as expected, the image scrolls nicely in its parent. Except when the view is scrolled (the effect is more visible if you scrolled to the bottom of the view), then disappear, and appear again (you switched to another view and came back) the scrolling value is restored, but the content of the scroll view is moved to the outside top part of its parent view. This is not simple to explain, I'll try to draw it: If you want to test/view the source (or the storyboard, I did not edit a single line of code). I put a little demo on my github: https://github.com/guillaume-algis/iOSAutoLayoutScrollView I did read the iOS…

Accepted Answer

Yeah, something strange happened with UIScrollView in pure autolayout environment. Re-reading the iOS SDK 6.0 release notes for the twentieth time I found that:

Note that you can make a subview of the scroll view appear to float (not scroll) over the other scrolling content by creating constraints between the view and a view outside the scroll view’s subtree, such as the scroll view’s superview.

Solution

Connect your subview to the outer view. In another words, to the view in which scrollview is embedded.

As IB does not allow us set up constraints between the imageView and a view outside the scroll view’s subtree, such as the scroll view’s superview then I've done it in code.

```
- (void)viewDidLoad {
    [super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
    [self.view removeConstraints:[self.view constraints]];
    [self.scrollView removeConstraints:[self.scrollView constraints]];
    [self.imageView removeConstraints:[self.imageView constraints]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[_scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_scrollView)]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_scrollView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_scrollView)]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[_imageView(700)]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_imageView)]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_imageView(1500)]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_imageView)]];
}
```

And vau! It works!

UIScrollView wrong offset with Auto Layout

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