constraints problems with containers

Question

OK I have a view-controller that sits in a container of another view.

MainView
  View
    Someview
    ContainerView (contains ContainedViewController)
    Otherview

ContainedViewController
   ContainedView (height can get resized during run).
      UILabel (varying height)
      UIView (fixed size, width & height)

Here's the thing... the view in ContainedViewController needs to get resized at runtime. It contains a label (that can grow depending on the text in it) and a static view directly below it, that never changes size

So, I have a constraint on the UILabel for it's height, and I change that at runtime, depending on how big it needs to be. There's a vertical constraint between the label and the fixed-view, and all of the "standard" constraints to the main superview.

When I run, though, I get "unable to simultaneously satisfy constraints", followed by the constraint log. Among the conflicting constraints are my new UILabel height, and then the height of ContainedView. I get a "UIView-Encapsulated-View-Height" problem with the ContainedView.

Apparently, "ContainedView"'s height is being dictated by the height of MainView's ContainerView.

What I want is for the ContainedView's height to change when the UILabel's height changes, and then have the propagate back up the containers, all the way to MainView. But I can't seem to get this to work.

How can I get the superview, and it's container view to resize when I change the size of my label?

Answer 1

In your main view controller, declare the following override:

- (void)viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];
    // Layout the container's content and get its resulting size
    [self.containedViewController.view layoutIfNeeded];
    CGSize containedViewSize = [self.containedViewController contentSize];
    // Now, use containedViewSize to set constraints on the view controller.
    self.containerHeightConstraint.constant = containedViewSize.height;
    self.containerWidthConstraint.constant = containedViewHeight.width;
}

Then, in your contained view controller, declare these properties:

@property (nonatomic, weak) IBOutlet UIView * contentView;
@property (nonatomic, weak) UIViewController * mainViewController;

In your storyboard make contentView a subview of the contained view controller's main view. Pin it with constraints to the main view's top left corner. Put whatever content you want in contentView, including constraints that determine contentView's size. (DON'T pin the contentView's length and width to the main view, however; that will cause conflicting constraints you described above.)

mainViewController should be set when preparing for the embed segue that sets up the container view controller.

And this method:

- (CGSize)contentSize {
    return self.contentView.frame.size;
}

Now, whenever you do something in the container view controller that affects the size of contentView, make the following call:

[self.mainViewController.view setNeedsLayout];

Sorry this isn't simpler, but it's the best solution I've found to this problem so far.