UITextView can't handle emojis with more than one Unicode codepoint

Originator:villev
Number:rdar://35050622 Date Originated:October 18 2017
Status:Open Resolved:No
Product:UIKit or Swift compiler Product Version:
Classification: Reproducible:Yes
 
Summary: 
UITextView text count is incorrectly calculated when using emojis where a single emoji contains more than one unicode codepoint. When typing emoji "👦🏿" to UITextView 64 times textView.text.characters.count will return the correct number: 64. However when typing 65 or more characters, the textView.text.characters.count will return double the correct amount: 65 -> 130, 66 -> 132 etc.

If using "👦"-emoji, which only has a single Unicode codepoint, the calculation is correct.


Steps to Reproduce:
Create a textview and insert 65 or more "👦🏿"-emojis in it and print textView.characters.count.

Expected Results:
65 or more

Actual Results:
130, 132, 134...

Version/Build:
XCode 9, Swift 3

Comments

Our team made some research on the issue.

Here is summary of the findings:

  • UITextView and UITextField seem to use NSBigMutableString as their internal buffer (i.e. when you invoke .text on them, that’s what gets returned)

  • When an NSBigMutableString that contains less or 256 UTF-16 units gets bridged to a Swift String, it works correctly

  • When an NSBigMutableString that contains more than 256 UTF-16 units gets bridged to a Swift String, grapheme clustering is not performed correctly — i.e. each code point gets converted to a Character, even ones that should be clustered together with previous code points (like variation selectors)

By villev at Oct. 19, 2017, 7:36 a.m. (reply...)

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