iOS: Getting height of views with programatically added constraints as only indicator

Question

Hello there fellow iOS programmers. While creating an app I've ran into a problem I can't seem to find an answer to. Let's lay it out:

I'm creating a UIViewController with a UIScrollView as it's only child. Inside this view I have a UIView, and inside of this there is a list of UIViews with UILabels inside them. As you all know you need to specify a contentSize for a UIScrollView. The problem is that the list needs to be dynamic with it's content, and I therefore have no way to know the views heights beforehand. I'm adding all views with constraints where the height is set to ">=0". When I later try to set the height of the UIScrollView I need to either get the height of the UIView that the list is inside, or get the origin.y and height of the last view in the list. This of course needs to be ready by the time the view is displayed to the user.

I've currently tried view.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize), which returned 0; view.systemLayoutSizeFittingSize(UILayoutFittingExpandedSize), which returned 10000; and view.origin.y + view.frame.height, which also returns 0. It seems to me like the constraints haven't taken effect yet.

I've tried setting both constraints and UIScollView.contentSize from viewDidLoad(). I've also tried to set constraints in viewDidLoad and setting contentSize in viewWillAppear; this yielded the same results. Setting constraints in viewWillAppear and setting contentSize in viewDidLoad only caused a crash.

Bottom-line: When should I set up the UIScrollView.contentSize if I want to get view.height or similar methods to return a correct result, while at the same time be ready by the time the user sees the view?

Btw, I'm making this app in Swift, so answers in this language is preferred, but I'm able to translate from Objective-C to Swift; post in whatever suits you best.

Thank you! :)

Answer 1

You say:

As you all know you need to specify a contentSize for a UIScrollView .

No, as TN2154 says, the constraints between the scroll view and its subviews are "interpreted as the content size of the scroll view" (emphasis added). This is a boon, because you no longer have to mess around with contentSize if doing auto-layout. Just set the constraints for the scroll view's subviews and the content size takes care of itself. This leverages the labels' intrinsic size (and make sure that the label's numberOfLines to zero).

The only trick is that it sometimes cannot figure out the correct width of the labels (because the trailing constraint is to the scroll view's content size, it will sometimes make the scroll view a horizontally scrolling one). You can remedy this by either manually setting preferredMaxLayoutWidth or by setting a width constraint between the label and the scroll view's superview.

Personally, while I understand the inclination to add the UIView containers between the scroll view and the labels, I'd suggest losing them unless you need them for some other reason. IMHO, it simply complicates the constraints unnecessarily. It's hairy enough as it is. Obviously, if these containers bear other utility for you, then go ahead and keep them (and they'll work fine), but if you're doing this simply for the sake of the constraints, you might consider eliminating them.