Open Radar

 
Area:
UIKit

Summary:
Adding the launch argument -UIViewShowAlignmentRects YES to debug alignment rectangles causes a crash if there is a UIViewEffectView in the view hierarchy. This happens for example with a plain `UIViewController` embedded in a navigation controller.

Steps to Reproduce:

1. Create a new Xcode project using the single view app template.
2. Modify the storyboard to embed the view controller in a navigation controller.
3. Edit the scheme to add and enable the following launch argument to the run action:
    -UIViewShowAlignmentRects YES
4. Build and run on a simulator

Expected Results:

The alignment rectangles of the views are displayed in yellow.

Actual Results:

Crashes with following console message:

2017-10-17 16:46:24.425431+0100 Alignment[24633:2704672] [LayoutConstraints] UIViewShowAlignmentRects is ON
2017-10-17 16:46:24.505213+0100 Alignment[24633:2704672] *** Assertion failure in -[UIVisualEffectView _addSubview:positioned:relativeTo:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3698.16.15/UIVisualEffectView.m:1464
2017-10-17 16:46:24.512331+0100 Alignment[24633:2704672] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: ' > has been added as a subview to  >. Do not add subviews directly to the visual effect view itself, instead add them to the -contentView.'

Version/Build:
iOS 11.0.1 (15A8401)
Xcode Version 9.0.1 (9A1004)