Auto Layout and sizeForChildContentContainer

Question

I have a content container view controller that adds a child view controller and then sets up some Auto Layout constraints to size the child view. The child view does not entirely fill the container's view. My child view controller implements viewWillTransitionToSize:withTransitionCoordinator: and lays out its contents based on the passed in size.

I know I need to override sizeForChildContent:withParentContainerSize: in the container view controller so that the child receives the correct size in its viewWillTransitionToSize: method. My question is, what's the correct way to calculate the size to return (i.e. the size the child view will be after the constraints are applied)? I could do some math to calculate the size of the child myself, but that kind of defeats the purpose of sizing the child view with Auto Layout.

Answer 1

Implement preferredContentSize in the child viewController

- (CGSize)preferredContentSize {
  return CGSizeMake(<width>, <height>);
}

Then the parent viewController can ask the child its preferred size, make any necessary adjustments, and return the adjusted size.