Open Radar

 
Summary: Starting from iOS 12 the layout is not performed until the content is scrolled to the end, which does not allow to position attachments properly. 

Notes:  According to documentation of `NSLayoutManager` it's stated that:

... both glyph generation and layout were always performed, in order, from the beginning to the end of the document.

And prior to iOS 12, setting `UITextView.attributedText` caused layout and as a result:

`NSLayoutManagerDelegate.layoutManager(_ layoutManager: NSLayoutManager, didCompleteLayoutFor textContainer: NSTextContainer?, atEnd layoutFinishedFlag: Bool)`

was called with `layoutFinishedFlag` set to true. As of iOS 12 it's not the case and this does not allow to update position of attachment glyphs.

Steps to Reproduce:
1) Build and run the TextViewTest sample application a device with iOS 12
2) Press the plus button in the navigation bar (perhaps several times for iPad)

Expected Results:
Text becomes bigger and positions of red and green rectangles is changed accordingly

Actual Results:
Red and green rectangles disappear (see attached screenshots)

Version/Build:
iOS 12.0 (16A366)

Additional information:
- Cannot be reproduced on iOS 10 and 11 as setting `UITextView.attributedText` causes layout (see attached backtrace for iOS 11.4)
- Can be worked around by calling `NSLayoutManager.ensureLayout(for container: NSTextContainer)` on updating `UITextView.attributedText` -- tap `Enable Workaround` in the sample application to check it out
- Cannot be reproduced if the content fits the screen or it's not "sparse" (contains lots of new lines, but continuous strings only)

Attachment can be found following the link: https://goo.gl/myQ7ft