View controllers without top in edgesForExtendedLayout temporarily receive an increased safeAreaInset during navigation transitions

Originator:steven.sheldon
Number:rdar://34349608 Date Originated:September 9 2017, 9:50 AM
Status:Open Resolved:
Product:iOS + SDK Product Version:11.0 (15A5361a)
Classification:Bug - UI/Usability Reproducible:Always
 
Area:
UIKit

Summary:
View controllers without top in edgesForExtendedLayout temporarily receive an increased safeAreaInset during navigation transitions. This happens during an animation, so scroll views whose contentInsetAdjustmentBehavior is not never will show a quick "bounce" during the transition.

Steps to Reproduce:
1. Run the attached repro project (or, build your own view controller with a scrollView and without top in edgesForExtendedLayout)
2. Tap the "Hello, World!" cell to push another view controller onto the navigation stack
3. Tap the back button to pop back to your original view controller with a scrollView
4. Observe during the transition that the scrollView initially starts too low and bounces back to the top by the end of the transition

Expected Results:
There should be no bounce while transitioning back to the view controller. This is the behavior under previous iOS versions.

Actual Results:
There is a bounce while transitioning back to the view controller. I've attached a video displaying this bounce and a screenshot showing that the top cell of the table is too low on the page during the transition.

Version/Build:
iOS 11.0 (15A5361a) built with Xcode 9 beta 6

Comments

Sounds similar to the issue reported in http://www.openradar.me/34256773

By steven.sheldon at Sept. 9, 2017, 5:06 p.m. (reply...)

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