Since the release of Xcode 8 and iOS 10, many developers have noticed a peculiar issue where views are not sized correctly within the viewDidLayoutSubviews method. This has stirred some frustration within the iOS development community, as accurate sizing is crucial for creating responsive and visually appealing applications. In this article, we'll explore the technical underpinnings of this issue, provide examples where relevant, and discuss possible solutions.

Understanding viewDidLayoutSubviews

In the UIKit framework, viewDidLayoutSubviews is a crucial method of the UIViewController lifecycle. This method is called when the view's bounds change and its subviews are laid out. Developers often override this method to make layouts respond dynamically to changes in view size or orientation.

Changes in iOS 10 and Xcode 8

With the introduction of Xcode 8 and iOS 10, Apple made significant improvements and optimizations to the layout processing system. While these changes were designed to enhance performance and flexibility, they also introduced some challenges, particularly for views' frame calculations within viewDidLayoutSubviews .

The Issue

The core issue is that, in some cases, the frames of the views are not set to their expected values when viewDidLayoutSubviews is called. This usually happens when using Auto Layout constraints. Views may not reflect changes in layout constraints or may not account for safe area insets properly.

Example:

Consider the scenario where a button needs to be centered within its parent view using Auto Layout constraints: