iphone - iOS Autolayout - Frame size not set in viewDidLayoutSubviews

Question

I'm working on a keyboard for iOS 8 using Autolayout to place the buttons on the view.
When I'm changing the layout using constraints, everything is appearing correctly on the screen, but when I want to know the view's frame size, I don't get the right size.

For example: I press a key, the keyboard layout changes and layouts everything according to my constraints. Then I want to know the size of any button on the screen - I do that in "viewDidLayoutSubviews" and get that result in the console:

2014-10-29 12:27:09.088 Keyboard[2193:60674] view did layout subviews
2014-10-29 12:27:09.088 Keyboard[2193:60674] {{inf, inf}, {0, 0}}

The button has the correct size and correct position, but when trying to get its frame the size is not set.

Where do I have to put my code when it is not working in viewDidLayoutSubviews?

I found a lot of questions on stackoverflow and other websited, but none of them covered my question.

Answer 1

I encountered a very similar issue (upvoted question) and found beeef's answer to point in the right direction. Given that Apple's documentation says not to call layoutSubviews() directly, I instead did as follows (where mySubView is a direct subview of self.view):

override func viewDidLayoutSubviews() {
    // self.view's direct subviews are laid out.
    // force my subview to layout its subviews:
    self.mySubView.setNeedsLayout()
    self.mySubView.layoutIfNeeded()

    // here we can get the frame of subviews of mySubView
    // and do useful things with that...
}

Just FYI, in my case mySubView is a UIScrollView, and I need to get the frame of one of its subviews, such that I can set the contentOffset accordingly before the view appears. I'm not sure whether viewDidLayoutSubviews() is the best place to do this, but it ensures that mySubView has been laid out.