Question

When using Storyboards, why does viewWillAppear not draw my subviews and viewDidLayoutSubviews does and more importantly to access the frame.size value from subviews of subviews I have to call [self.scroller layoutIfNeeded] inside of viewDidLayoutSubviews? I’m interested in understanding the page life cycle of a view controller and what changed in going from xibs to storyboards.

Answer 1

Storyboards are actually implemented as collections of xib files, with additional information about transitions (segues) between them. So the view controller life cycle should not be radically different if we’re just talking about a single view controller.

It’s very difficult to answer your specific question without understanding how your view controller and its view hierarchy are set up. It sounds like you have a view inside of a scroll view and you want to know when you can access its frame property.

UIKit follows these steps (roughly):

1. It loads all the views described in the storyboard/xib file and connects all the actions and outlets as needed. viewDidLoad is called after this step.
2. It calls viewWillAppear: to indicate that it is about to display the view.
3. It adds the view to the window, sizing it to fit. The sizing propagates down the view hierarchy, so each view lays out its subviews (if it is configured to autoresize subviews). These changes occur inside an animation block, so once everything is set up the user sees the new view animated into place.
4. Once animations are complete, viewDidAppear: is called.

It’s possible you are seeing something strange if a view has autoresizesSubviews set to NO; that may be why you have to call layoutIfNeeded on self.scroller. Note that the documentation for layoutIfNeeded says:

When this message is received, the layer’s super layers are traversed until a ancestor layer is found that does not require layout. Then layout is performed on the entire layer-tree beneath that ancestor.

So it could potentially be triggering the layout of other unrelated views.