如何使用自动布局根据其子视图调整父视图的高度

Question

I have cutomized a view, whose subviews's height will dynamically change(I'm changing the height by changing the constraint). My intention is to let the view's height adjust to its subviews' height, so I won't care for anything, and that's what autolayout is for.

In practise, there is no way to add any constraints to the root view in IB. And I found I can still change the frame of the root view, which appears to be able to solve my current problem. But I don't think it's recommended to compound auto layouts and frames.

So, any other suggestions?

Answer 1

It's perfectly fine to have some views using the old system of layout (ie, autoresizing and frame setting) while other views are using Auto Layout directly. The important thing to remember is to set the translatesAutoresizingMaskIntoConstraints property to NO on views instantiated in code that are using Auto Layout.

However, you can't use Auto Layout on a view controller's root view.

Using Auto Layout, subviews can dictate the size of their superview–but this won't work if the superview is using autoresizing and frame setting.

I don't know if the root view you're working with is the root view of a scene's main view controller or the root view of a child view controller. If the former, I don't recommend adjusting the root view's frame in iOS 7. Just let the root view fill the whole screen (which is its default behavior).

Answer 2

Subviews have their size dictated by their superview, not the other way around. For your special case, I would make the subview delegate its height changes back to the superview. While you could then adjust the rect of the superview (and avoid changing the subview's height altogether), I would do this:

1. Create a subview of your view controller that behaves as your new resizing parent. The viewController.view can then remain fullscreen. Your view hierarchy would then be viewController.view->Resizing Parent->Resizing Child.
2. Create an IBOutlet to the constraint you want to modify.
3. Create a protocol for the child view to send resize callbacks to its parent.
4. Update the parent's constraint constant when it receives the callback.

You shouldn't have to modify the height of the child view, because the constraints will do that for you.